Sony Trinitron Flat Screen CRT TVs - KV HW21 Series Circuit diagram
Click on the schematics to magnify
Processor Block
Audio Block
SMPS (Power Regulator)
Deflection
Tuner
Input jack block
CRT base card
Friday, June 10, 2016
Wednesday, June 08, 2016
Samsung DVD HD860 – SMPS, Servo, video decoder Circuit diagram
Samsung
HD860 Multi Region Code Free HDMI PAL/NTSC DVD Player. Used ICs: ICE3B0365 – FAN8026 – ZR36888
720p/1080i
up conversion
Plays
All-Region DVDs: Region 1, 2, 3, 4, 5, 6, 0
Plays
PAL and NTSC Region DVDs on all TVs
HDMI
output
DivX(MPEG4)playback
SMPS schematic [Click on the pictures to magnify]
Servo and Motor driver
AV decoder
DVD
mechanism - Exploded
Picture
Quality Defect (Prevention of NDF)
TV
shows low picture quality. (Ex) Blotting colors… In most cases, above symptom is not real
defect. This is caused by lack of
knowledge regarding "Picture quality Function”. If you receive the units that is requested
Repair or Return by customer, adjust picture quality in the Menu.
1. Press
the MENU button.
2.
Select the Setup on the screen.
3.
Select the Display Setup.
4. You can see the"Picture Quality" category.
5. Select the Picture quality.
6. You can adjust"Sharpness" & " Brightness" & " Color Saturation"
4. You can see the"Picture Quality" category.
5. Select the Picture quality.
6. You can adjust"Sharpness" & " Brightness" & " Color Saturation"
7.
Before repairing or exchanging, adjust above menu first.
ASSY
PCB-SMPS;DVD-HD860,ASSY PCB-S > AK92-00862C
ASSY
PCB-MAIN DVD;DVD-HD860/XEV,MA > AK92-00847C
ASSY-PICK
UP;MOLD,MAXINO/MIDAS,Pic > AK97-01660A
Sunday, June 05, 2016
LG RU52 LG RU60 LCD Projection TV How to replace the Lamp Lamp time reset SMPS circuit diagram
Power Supply Regulator Schematic – Lamp replacement
procedure - LG
RU-52SZ30 RU-60SZ30 LCD PROJECTION TV
Lamp
Replace
Use it when the Lamp time is ‘0’.
Press the IN-START key on R/C for adjustment to select
Lamp replace and adjust with volume key.
Press the IN-START key on R/C for adjustment to select
Lamp replace and adjust with volume key.
You
must replace the lamp when
The projector image get darker or start to be deteriorated.
The lamp indicator is red (red, flashing alternately).
The massage “LAMP REPLACE”appears on the screen when turning the projector lamp on.
The projector image get darker or start to be deteriorated.
The lamp indicator is red (red, flashing alternately).
The massage “LAMP REPLACE”appears on the screen when turning the projector lamp on.
Replace
the lamp as below sequence
1. Turn off the projector and unplug the power cable. (Cool the lamp for more than 1 hour.)
2. Remove the four retaing screws on the lamp cover with a screwdriver of “+“ type and then lift off the lamp cover.
3. After lifting the lamp cover off, remove the two retaing screw on lamp case with screwdriver of “-“ type. (refer to fig.2)
4. Lift up the fixed wire handle of the lamp. (refer to fig.3)
5. Pull out the handle slowly and remove the lamp case.
6. Insert the new lamp gently into the correct position. Make sure it is inserted correctly.
7. Tighten the screw you removed in step 3.
8. Replace the lamp cover and tighten the cover screws. (Make sure the lamp cover is securely fastened. If lamp cover is open, the lamp indicator flashes green and the projector is not turn on.)
1. Turn off the projector and unplug the power cable. (Cool the lamp for more than 1 hour.)
2. Remove the four retaing screws on the lamp cover with a screwdriver of “+“ type and then lift off the lamp cover.
3. After lifting the lamp cover off, remove the two retaing screw on lamp case with screwdriver of “-“ type. (refer to fig.2)
4. Lift up the fixed wire handle of the lamp. (refer to fig.3)
5. Pull out the handle slowly and remove the lamp case.
6. Insert the new lamp gently into the correct position. Make sure it is inserted correctly.
7. Tighten the screw you removed in step 3.
8. Replace the lamp cover and tighten the cover screws. (Make sure the lamp cover is securely fastened. If lamp cover is open, the lamp indicator flashes green and the projector is not turn on.)
Resetting
the lamp time
After pressing the “?“ key on the remote control in Stand-By mode, press the “9876“ and press the “OK“ button.
And then three LED in the front is stop after flashing for a moment.
After pressing the “?“ key on the remote control in Stand-By mode, press the “9876“ and press the “OK“ button.
And then three LED in the front is stop after flashing for a moment.
Lamp
Life Time Confirmation
Method1 : Enter ADJ mode with using the remote control. You can be confirmed because “ Lamp Life Time XX hr“ is appeared.
Method2 : With using the remote control offered to consumer if you press the menu button continuously, OSD menus will disappear then press the “9876“ and press the “OK“ button to enter ADJ mode you can see “Lamp Life Time XX hr“
Method1 : Enter ADJ mode with using the remote control. You can be confirmed because “ Lamp Life Time XX hr“ is appeared.
Method2 : With using the remote control offered to consumer if you press the menu button continuously, OSD menus will disappear then press the “9876“ and press the “OK“ button to enter ADJ mode you can see “Lamp Life Time XX hr“
SMPS circuit diagram
Saturday, June 04, 2016
Philips LCD TV Power Supply 22HFL3232-10 - 19inch and 22inch LCD TV - Circuit Diagram and PWB - Top and Bottom Side
Used Semiconductors: LD7576AGR –
AO4443 – STP10NK70ZFP(FET)
SMPS and Printed circuit board - Top & Bottom view
Click on the pictures to zoom in
Hyundai 42 inch Plasma TV SMPS USP490M-42LP Circuit Diagram
Hyundai
Plasma TV – 42 inch – Power Supply Regulator board - Schematic
Used ICs: UC3854DW
– KA7552 – TOP243P - 11N80C(FET)
Click on the schematic to magnify
Friday, June 03, 2016
Water damage - LG Dishwasher LDS4821 – Error Codes – Wiring diagram
To lock/unlock the buttons, press QUICK and RINSE ONLY
simultaneously for 3 seconds. When CHILD LOCK is set, all buttons are disabled.
To cancel a running cycle, open the door, then press and hold the
POWER SCRUB and NORMAL buttons together for 3 seconds. The drain pump will be
activated and the cycle will be canceled.
Pressing the POWER button turns on power to the control. After the cycle is complete, the power
automatically switches off after 4 minutes for safety and economy. If there is an unusual Power surge or
disturbance, the power will be automatically turned off for safety and the
cycle will have to be started over.
Wiring Diagram
Click on the pictures to zoom in
ERROR MESSAGES
1E display => INLET ERROR: Not reached to the
normal water level in spite of 10 min. water supply.
The Water Supply Tap is closed.
The Water Supply is shut off.
The Inlet Hose is kinked.
The Water Pressure is very low. (below 10 psi)
Inlet Valve is OK?
The filter of Inlet Valve is clogged by impure water.
The Hall sensor is OK?
The Impeller of Air Guide is bound.
The Inlet Hose is kinked.
The Water Pressure is very low. (below 10 psi)
Inlet Valve is OK?
The filter of Inlet Valve is clogged by impure water.
The Hall sensor is OK?
The Impeller of Air Guide is bound.
Take action on Water Supply device.
Measure the electric resistance of Inlet Valve. (950-1300 )
Clean the filter of Inlet Valve.
Check the frequency of Inlet Water by the Test Mode.
Replace the Air Braker.
Measure the electric resistance of Inlet Valve. (950-1300 )
Clean the filter of Inlet Valve.
Check the frequency of Inlet Water by the Test Mode.
Replace the Air Braker.
0E
display => DRAIN ERROR: Not fully drained out in spite of 5 min. drain operation.
The Drain Hose kinked or blocked.
Wiring connection is OK?
The drain outlet of sump is blocked.
The Drain Pump/Motor or circuit is troubled.
Wiring connection is OK?
The drain outlet of sump is blocked.
The Drain Pump/Motor or circuit is troubled.
Remove the cause of kink or block.
Check the wiring connection.
Measure the electric resistance of Drain Motor. (20-40 )
Replace the Drain Motor or repair the Circuit.
Check the wiring connection.
Measure the electric resistance of Drain Motor. (20-40 )
Replace the Drain Motor or repair the Circuit.
E1 display => LEAKAGE
ERROR: The excessive RPM of Washing Motor happened during Wash cycle due
to water leakage.
Water leakage in Hose connections.
Water is leaked by damages.
The Motor Water Seal leakage of Sump assembly.
The height of Drain Hose connection (sink-Drain Hose) is not over 20″.
Impeller of the Washing Pump is worn away.
Water is leaked by damages.
The Motor Water Seal leakage of Sump assembly.
The height of Drain Hose connection (sink-Drain Hose) is not over 20″.
Impeller of the Washing Pump is worn away.
Replace the connections of Hose.
Check the point of damages and repair or replace the related parts.
Read the Installation Instructions and fix it to the recommended Height.
Replace the Impeller of the Washing Pump.
Check the point of damages and repair or replace the related parts.
Read the Installation Instructions and fix it to the recommended Height.
Replace the Impeller of the Washing Pump.
FE display => EXCESS
ERROR: Excessive water is supplied than normal water level.(Automatically
drain Pump operated.)
The Inlet Valve is troubled.
The Controller is troubled.
The Controller is troubled.
Replace the Inlet Valve.
Repair or replace the Controller.
Repair or replace the Controller.
tE display => THERMAL
ERROR: The resistance of thermistor not normally out put.
The Inlet Water Temperature is very high. (over 194 )
Wiring connection is OK?
The Thermistor is OK?
Wiring connection is OK?
The Thermistor is OK?
Check the temperature. (Test Mode).
If the temperature is displayed, adjust the Inlet Water Temperature
to 120.
If the temperature is not displayed, check the wiring connection. Check the electric resistance of Thermistor. (11~14k
at 77 )
Replace the PCB.
LE display => MOTOR
ERROR: The Motor is working abnormally.
Wiring connection is OK?
The Impeller of Washing Pump is locked.
The rotor of Washing Motor is locked.
The Blade is locked.
The Impeller of Washing Pump is locked.
The rotor of Washing Motor is locked.
The Blade is locked.
Check the wiring connection.
Replace the cause of restriction.
Replace the Washing Motor.
Replace the PCB.
Replace the cause of restriction.
Replace the Washing Motor.
Replace the PCB.
Test Mode LDS4821 Series dishwashers
Thursday, June 02, 2016
PLX Series QSC PLX 1202 PLX 1602 PLX 2402 PLX 3002 Troubleshooting
Power Supply - - Replacing Blown IGBTs.
The PLX IGBTs are driven by an active, direct coupled integrated
circuit, rather than a gate drive transformer. IGBT or driver failure should be
rare (when correctly assembled) but when the IGBT’s blow, it usually damages
the following parts:
CHECKLIST AFTER BLOWN IGBT’S
Q96, Q97, (IGBT’s generally fail in pairs)
D78, D79, R358, R359, gate drive coupling comonents, check after removing blown IGBT’s.
Ul8, lR2110 high-side gate driver, Fault current when low-side IGBT shorts to upper rail. Such currents also typically damage the gate coupling parts noted above.
Ul9, 3525 controller, Blows from currents shorted thru Ul8, or possibly by overvoltage on the supply rail SOMETIMES Ul4, 556, powered from 5V output of 3525, which may fail high when 3525 fails.
RARELY Ul3, which has fairly high supply voltage ratings.
PROBABLE CAUSES OF MASSIVE IGBT FAULTS
SHORTS IN CONTROL CIRCUIT.
The parts operate well within their ratings and should hold up well in the field. The usual cause of failure is when both IGBT’s turn on at once, shorting Pri-Hi to Pri-Lo. This occurs when something causes the drive signal to one part to remain on when the other part is supposed to turn on. Shorts from solder or debris are one obvious cause.
SHORTS IN THE LOAD.
Although there is peak current shutdown, shorts in the power amplifier transistors or secondary-side supply components can cause currents to increase too quickly to prevent damage.
OVERVOLTAGE ON THE BIAS SUPPLY.
If the TOP-210 bias supply fails to operate, no harm occurs, the unit simply does not operate.
However, open circuit (missing part) in several key components can cause the Bias supply voltage to be much too high, This blows the 2110 and thus the IGBT’s.
QUICK TEST OF BIAS SUPPLY.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working normally, the green “power” LED should come on between 30 and 35Vz with its usual, steady “half-brighr start-up level. If the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V until you have measured the bias voltage. The switching will not start until you reach 9OV, so you can save the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V. Open or missing D63, 64, 65, 66, 67 or R349 will break the feedback to U16 and cause overvoltage.
D78, D79, R358, R359, gate drive coupling comonents, check after removing blown IGBT’s.
Ul8, lR2110 high-side gate driver, Fault current when low-side IGBT shorts to upper rail. Such currents also typically damage the gate coupling parts noted above.
Ul9, 3525 controller, Blows from currents shorted thru Ul8, or possibly by overvoltage on the supply rail SOMETIMES Ul4, 556, powered from 5V output of 3525, which may fail high when 3525 fails.
RARELY Ul3, which has fairly high supply voltage ratings.
PROBABLE CAUSES OF MASSIVE IGBT FAULTS
SHORTS IN CONTROL CIRCUIT.
The parts operate well within their ratings and should hold up well in the field. The usual cause of failure is when both IGBT’s turn on at once, shorting Pri-Hi to Pri-Lo. This occurs when something causes the drive signal to one part to remain on when the other part is supposed to turn on. Shorts from solder or debris are one obvious cause.
SHORTS IN THE LOAD.
Although there is peak current shutdown, shorts in the power amplifier transistors or secondary-side supply components can cause currents to increase too quickly to prevent damage.
OVERVOLTAGE ON THE BIAS SUPPLY.
If the TOP-210 bias supply fails to operate, no harm occurs, the unit simply does not operate.
However, open circuit (missing part) in several key components can cause the Bias supply voltage to be much too high, This blows the 2110 and thus the IGBT’s.
QUICK TEST OF BIAS SUPPLY.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working normally, the green “power” LED should come on between 30 and 35Vz with its usual, steady “half-brighr start-up level. If the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V until you have measured the bias voltage. The switching will not start until you reach 9OV, so you can save the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V. Open or missing D63, 64, 65, 66, 67 or R349 will break the feedback to U16 and cause overvoltage.
QUICK TEST OF BIAS SUPPLY.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working normally, the green “power” LED should come on between 30 and 35V, with its usual, steady “half-brighf’ start-up level.
CAUTION: if the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V until you have measured the bias voltage. The switching will not start until you reach9OV, so you can save the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V.
BIAS SUPPLY VOLTAGE MUCH TOO HIGH
D63,64,65,66,67 or R349 open or missing -- breaks feedback to U16
NO BIAS SUPPLY VOLTAGE
U16 missing or blown.
Tl missing, reversed, or open primary
D62 open or missing.
BIAS VOLTAGE ERRORS
The exact voltage is controlled by the feedback through D63, 64_ 65, 66, 67 and R349 as follows:
Cl38 is the “+18V’ rail with about 18.8V typical.
D63, 64, 65 each subtract a diode drop (0.7V) from Cl38.
Cl39 , is the “+16V” rail with about 16.6V typcial.
D66, a IOV zener diode , plus diode D67, subtract about 1 IV from +16.6V.
R349 subtracts about 0.5V, bringing the net voltage at Ul6, feedback pin 4, to about 5.lV.
Ul6 uses this feedback to adjust the “on” time at pin 5, in order toraise or lower the flyback voltage charging Cl38 and thus maintain regulation of the +16V and +18V supplies C142, R356, and R349 form a closed-loop stability circuit which prevents the regulated voltage from “hunting”.
Q99 and associated R374 reduce the voltage of the Bias supply by 33% when the AC voltage is turned off.
This prevents the Power LED from showing at half brightness after turn-off, since U16 continues to run from the main filters for some time after shut down R375 and 376 sense the output of Ul3:3, the “Loss of AC” comparator, and cause Q99 to turn on. If Q99 is shorted, the bias voltages will remain 33% low when AC is turned on.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working normally, the green “power” LED should come on between 30 and 35V, with its usual, steady “half-brighf’ start-up level.
CAUTION: if the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V until you have measured the bias voltage. The switching will not start until you reach9OV, so you can save the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V.
BIAS SUPPLY VOLTAGE MUCH TOO HIGH
D63,64,65,66,67 or R349 open or missing -- breaks feedback to U16
NO BIAS SUPPLY VOLTAGE
U16 missing or blown.
Tl missing, reversed, or open primary
D62 open or missing.
BIAS VOLTAGE ERRORS
The exact voltage is controlled by the feedback through D63, 64_ 65, 66, 67 and R349 as follows:
Cl38 is the “+18V’ rail with about 18.8V typical.
D63, 64, 65 each subtract a diode drop (0.7V) from Cl38.
Cl39 , is the “+16V” rail with about 16.6V typcial.
D66, a IOV zener diode , plus diode D67, subtract about 1 IV from +16.6V.
R349 subtracts about 0.5V, bringing the net voltage at Ul6, feedback pin 4, to about 5.lV.
Ul6 uses this feedback to adjust the “on” time at pin 5, in order toraise or lower the flyback voltage charging Cl38 and thus maintain regulation of the +16V and +18V supplies C142, R356, and R349 form a closed-loop stability circuit which prevents the regulated voltage from “hunting”.
Q99 and associated R374 reduce the voltage of the Bias supply by 33% when the AC voltage is turned off.
This prevents the Power LED from showing at half brightness after turn-off, since U16 continues to run from the main filters for some time after shut down R375 and 376 sense the output of Ul3:3, the “Loss of AC” comparator, and cause Q99 to turn on. If Q99 is shorted, the bias voltages will remain 33% low when AC is turned on.
REPLACING BLOWN TOP-210.
If U16 has blown, check T-l for continuity after removing Ul6. Its primary may be open. Pins I-2 It should measure about 15 ohms.
If U16 has blown, check T-l for continuity after removing Ul6. Its primary may be open. Pins I-2 It should measure about 15 ohms.
Replacing Blown Output Transistors
OUTPUT TRANSISTOR SHORTED
Short in one device tend to cause the opposing device to blow as well,
If an output transistor shorts:
Drive transistor will be shorted (Q26, Q27, Q71, Q72)
CXNne transistors will short in pairs (Q39 & Q40, Q36 & Q37, Q84 8 Q85, Q81 8, Q82)
The rest will short in fours (Q28, Q29, Q34 & Q35; Q73, Q74, Q79 8, Q80)
IGBT’s 8 their associated components may fail
Short in one device tend to cause the opposing device to blow as well,
If an output transistor shorts:
Drive transistor will be shorted (Q26, Q27, Q71, Q72)
CXNne transistors will short in pairs (Q39 & Q40, Q36 & Q37, Q84 8 Q85, Q81 8, Q82)
The rest will short in fours (Q28, Q29, Q34 & Q35; Q73, Q74, Q79 8, Q80)
IGBT’s 8 their associated components may fail
CHECK EMITTER AND BASE RESISTORS WHILE DEVICES ARE REMOVED,
Each output transistor has an associatated pair of 0.47 ohm resistors in parallel.
Each BANK of output transistors has a 15 ohm resistor from base to rail (emitter bus).
Each output transistor has an associatated pair of 0.47 ohm resistors in parallel.
Each BANK of output transistors has a 15 ohm resistor from base to rail (emitter bus).
Audio Outputs Troubleshooting Current Limit
WEAK CURRENT LIMIT -- PREMATURE CLIPPING.
The usual symptom of weak output current is premature clipping of one or more peaks of the audio voltage.
This could be caused by missing step, weak current limit, or dead output section.
PREMATURE CLIPPING at 60% VOLTAGE, SIMILAR AT ALL IMPEDANCES:
This points to a step problem (2402, 3002 only). See Step Troubleshooting.
If the amplifier reaches full voltage at 8 ohms, but prematurely clips at 4 ohms or 2 ohms, we can assume the step is OK but the output current is too low (see below).
NO OUTPUT AT ALL ON ONE POLARITY.
This indicates complete failure (open circuit) in the circuit leading to the dead output polarity. Check the series components in the current splitter for missing or open:
Ch 1: Positive, Ql9, R381, Q20, R70, DIO, D14. Negative: Q22, R382, Q21, R71, Dl I, D12
Ch 2: Positive, Q64, R383, Q65, Rl93, D35, D39. Negative: Q67, R384, Q66, Rl94, D36, D37
CONSTANT, PREMATURE CLIPPING, WORSE AT LOW IMPEDANCES.
First, check the clamping voltages on C21 (Ch I+), C22 (Ch I-), C56 (Ch 2+), C57 (Ch 2-), as shown in table below. At idle, all four voltages should all be similar. If one is out, check parts according to the
following table. The exact voltage varies with temperature. Look for the mismatching value on the weak cell.
A too-low voltage causes early clamping of that output section, as explained in the previous several pages. If the voltage is correct and current is still low, also check for missing - unsoldered output device, or emitter resistors.
The usual symptom of weak output current is premature clipping of one or more peaks of the audio voltage.
This could be caused by missing step, weak current limit, or dead output section.
PREMATURE CLIPPING at 60% VOLTAGE, SIMILAR AT ALL IMPEDANCES:
This points to a step problem (2402, 3002 only). See Step Troubleshooting.
If the amplifier reaches full voltage at 8 ohms, but prematurely clips at 4 ohms or 2 ohms, we can assume the step is OK but the output current is too low (see below).
NO OUTPUT AT ALL ON ONE POLARITY.
This indicates complete failure (open circuit) in the circuit leading to the dead output polarity. Check the series components in the current splitter for missing or open:
Ch 1: Positive, Ql9, R381, Q20, R70, DIO, D14. Negative: Q22, R382, Q21, R71, Dl I, D12
Ch 2: Positive, Q64, R383, Q65, Rl93, D35, D39. Negative: Q67, R384, Q66, Rl94, D36, D37
CONSTANT, PREMATURE CLIPPING, WORSE AT LOW IMPEDANCES.
First, check the clamping voltages on C21 (Ch I+), C22 (Ch I-), C56 (Ch 2+), C57 (Ch 2-), as shown in table below. At idle, all four voltages should all be similar. If one is out, check parts according to the
following table. The exact voltage varies with temperature. Look for the mismatching value on the weak cell.
A too-low voltage causes early clamping of that output section, as explained in the previous several pages. If the voltage is correct and current is still low, also check for missing - unsoldered output device, or emitter resistors.
Audio Power Stage, Current Limit Troubleshooting
CURRENT LIMITS WHICH COLLAPSE PREMATURELY.
An immediate collapse of ALL current limits at full power could be premature triggering of “Power Supply Cutback”, which is described in the section below. Cutback after several seconds of full power operation at two ohms is normal.
Cutback of one or more output sections, at full temperature, while approaching full power into two ohms is also normal. However, cutbacks at 4 ohms, or when cold into two ohms, indicate problems with the transistor power measuring circuitry.
An immediate collapse of ALL current limits at full power could be premature triggering of “Power Supply Cutback”, which is described in the section below. Cutback after several seconds of full power operation at two ohms is normal.
Cutback of one or more output sections, at full temperature, while approaching full power into two ohms is also normal. However, cutbacks at 4 ohms, or when cold into two ohms, indicate problems with the transistor power measuring circuitry.
CLAMPING VOLTAGES COLLAPSE TOO SOON.
TROUBLESHOOTING “POWER SUPPLY CUTBACK”.
As noted in the section on Power Supply, the amplifier’s current limit cuts back when necessary to protect the power supply. Because the Observed effect is a reduced output voltage, in response to prolonged operation above the long-term current limit, we commonly refer to this behavior as “power supply cutback”, but we must remember that it is actually amp/Tier current hmifhg in response to an overload signal sent from the power supply. Full power operation into 2 ohms (both channels) should produce a 50% cutback of current after several seconds.
If both channels of the amplifier fail to cut back after about 3 seconds, 2-ohms, both channels driven, the cutback signal is probably missing. CAUTION: Prolonged operation under these conditions could blow IGBT or burn out Cl44. Test for 6-10 seconds maximum.
Check the output (secondary side) pins of U17 (sh 4). Confirm presence of +6V on pin 5. Pin 4 should normally be at about OV, and go high (I-5V) after 3 seconds at full power, If Ul7-pin 4 does not go high, check U17 itself. If it appears OK, trace the circuitry driving U17 (PRIMARY SIDE, CAUTION). Check for continuity through L6:2 to Pri-Lo, check missing or open R343, D61, Q95, R347, all of which drive optocoupler U17. A short in R346 or Cl31 will also prevent drive to U17.
If Ul7-pin 4 goes high on schedule, and BOTH channels fail to cut back, trace voltage on“PS_OL” bus to R273 (sh 3), which connects to “MUTE+” bus. Continue tracing voltage on MUTE+ to Ql6 (sh I) and Q61 (sh 2). If only ONE channel fails to cut back, look for missing Ql6, R 65, Ql7 (sh I) or Q61, Rl88, Q62 (sh 2).
Cl31 controls the speed of cutback.. If missing, the amplifier current limits will enter cutback almost immediately at or above full power, 4 ohms.
As noted in the section on Power Supply, the amplifier’s current limit cuts back when necessary to protect the power supply. Because the Observed effect is a reduced output voltage, in response to prolonged operation above the long-term current limit, we commonly refer to this behavior as “power supply cutback”, but we must remember that it is actually amp/Tier current hmifhg in response to an overload signal sent from the power supply. Full power operation into 2 ohms (both channels) should produce a 50% cutback of current after several seconds.
If both channels of the amplifier fail to cut back after about 3 seconds, 2-ohms, both channels driven, the cutback signal is probably missing. CAUTION: Prolonged operation under these conditions could blow IGBT or burn out Cl44. Test for 6-10 seconds maximum.
Check the output (secondary side) pins of U17 (sh 4). Confirm presence of +6V on pin 5. Pin 4 should normally be at about OV, and go high (I-5V) after 3 seconds at full power, If Ul7-pin 4 does not go high, check U17 itself. If it appears OK, trace the circuitry driving U17 (PRIMARY SIDE, CAUTION). Check for continuity through L6:2 to Pri-Lo, check missing or open R343, D61, Q95, R347, all of which drive optocoupler U17. A short in R346 or Cl31 will also prevent drive to U17.
If Ul7-pin 4 goes high on schedule, and BOTH channels fail to cut back, trace voltage on“PS_OL” bus to R273 (sh 3), which connects to “MUTE+” bus. Continue tracing voltage on MUTE+ to Ql6 (sh I) and Q61 (sh 2). If only ONE channel fails to cut back, look for missing Ql6, R 65, Ql7 (sh I) or Q61, Rl88, Q62 (sh 2).
Cl31 controls the speed of cutback.. If missing, the amplifier current limits will enter cutback almost immediately at or above full power, 4 ohms.
SHORT CIRCUIT CURRENT DOESN’T CUT BACK.
CAUTION: DO NOT MAINTAIN A SHORTED LOAD IF CUTBACK FAILS TO OCCUR WITHIN 1 SECOND.
It will be necessary to measure the output current with a DC current probe, or by noting the voltage across a low value resistance with a DC scope, in order to determine which output cell is failing to cut back. Failure to cut back could indicate either lack of clamping, or lack of voltage cutback. Measure the voltage on the respective clamp capacitor. If the voltage decreases, but current limiting does not cut back, check the clamping transistor.
CAUTION: DO NOT MAINTAIN A SHORTED LOAD IF CUTBACK FAILS TO OCCUR WITHIN 1 SECOND.
It will be necessary to measure the output current with a DC current probe, or by noting the voltage across a low value resistance with a DC scope, in order to determine which output cell is failing to cut back. Failure to cut back could indicate either lack of clamping, or lack of voltage cutback. Measure the voltage on the respective clamp capacitor. If the voltage decreases, but current limiting does not cut back, check the clamping transistor.
Troubleshooting Thermal Tracking
MOUNTING PROBLEMS WITH IOK SENSING NTC.
The thermal sensing for fan and bias tracking depends on a 1 OK NTC which is mounted in a hole in the heat sink. The hole is filled with thermal grease to improve coupling. If the NTC is not straight while mounting the heat sink, it may short out against the side of its hole. It is mounted on a standoff which protrudes into the hole, so this should not occur if care is taken while installing the heatsink. If shorted to the heat sink, the amplifier output voltage is coupled to the NTC. If the short is to the grounded lead of the NTC, it may not damage anything. If to the other end, a large voltage is put across the NTC which will probably damage it.
SHORT FROM “LIVE” END OF NTC TO HEAT SINK:
Replace affected NTC
BE AWARE: This can short (relatively) quietly and then appear to be operating normally. Poor bias tracking can indicate this problem. Sometimes this short will not happen until the amplifier is driven past IV input.
NTC BENT OVER AND SHORTED TO DRIVER TRANSISTORS.
May touch Ql9, Q26, or Q64, Q71.
This causes severe overcurrent to the affected output cell, possibly damaging the parts in series with the shorted transistor. It may also blow the power supply
The thermal sensing for fan and bias tracking depends on a 1 OK NTC which is mounted in a hole in the heat sink. The hole is filled with thermal grease to improve coupling. If the NTC is not straight while mounting the heat sink, it may short out against the side of its hole. It is mounted on a standoff which protrudes into the hole, so this should not occur if care is taken while installing the heatsink. If shorted to the heat sink, the amplifier output voltage is coupled to the NTC. If the short is to the grounded lead of the NTC, it may not damage anything. If to the other end, a large voltage is put across the NTC which will probably damage it.
SHORT FROM “LIVE” END OF NTC TO HEAT SINK:
Replace affected NTC
BE AWARE: This can short (relatively) quietly and then appear to be operating normally. Poor bias tracking can indicate this problem. Sometimes this short will not happen until the amplifier is driven past IV input.
NTC BENT OVER AND SHORTED TO DRIVER TRANSISTORS.
May touch Ql9, Q26, or Q64, Q71.
This causes severe overcurrent to the affected output cell, possibly damaging the parts in series with the shorted transistor. It may also blow the power supply
Replace affected NTC, drive transistors, check components in
series with drive transistor
Ch 1: Ql9 shorted, check, R381, Q20, R70, DIO, D14.
Q26 shorted, check ALL outputs and opposing driver transistor on this channel.
Q26 shorted, check ALL outputs and opposing driver transistor on this channel.
Ch 2: Q64 shorted, check R383, Q65, Rl93, D35, D39.
Q71 shorted, check ALL outputs and opposing driver transistor on this channel.
Q71 shorted, check ALL outputs and opposing driver transistor on this channel.
Audio Output, Troubleshooting Stability Feedback
HIGH FREQUENCY OSCILLATIONS
SEVERE-DRAWS CURRENT-GROSS DISTORTION
C27 (62) missing or wrong, or series R367 (368)
C 25, 26 (60, 61) missing
Secondary filter capacitors missing or open (unlikely that ALL are defective).
SEVERE, BUT DOES NOT DRAW LARGE CURRENT
R22 (146) open.
MARGINAL -- MAY APPEAR ONLY AS EXCESS DISTORTION
Cl4 (49) missing
Cl 6 (50) missing or too large
C28 (63) missing
C 25 or 26 (60 or 61) missing or too large
Cl95 or 196 missing (input board).
EXCESSIVE OSCILLATION JUST BELOW CLIPPING, 2-4 ohms
Cl 7 (52) missing
NOTE: about 0.1% oscillation right below clipping at 2 ohms is normal.
EXCESSIVE SWITCHING INTERFERENCE.
Switching interference may LOOK like an instability, however it is at a much lower frequency (1lOkH.z) than most instabilities. It will be more visible at low frequencies (2OOHz) and at lower impedances.
Missing jumper at R224.
Missing Cl29, 134 on output board.
Grounds not connected to chassis at output board and front chassis mounting screw.
SEVERE-DRAWS CURRENT-GROSS DISTORTION
C27 (62) missing or wrong, or series R367 (368)
C 25, 26 (60, 61) missing
Secondary filter capacitors missing or open (unlikely that ALL are defective).
SEVERE, BUT DOES NOT DRAW LARGE CURRENT
R22 (146) open.
MARGINAL -- MAY APPEAR ONLY AS EXCESS DISTORTION
Cl4 (49) missing
Cl 6 (50) missing or too large
C28 (63) missing
C 25 or 26 (60 or 61) missing or too large
Cl95 or 196 missing (input board).
EXCESSIVE OSCILLATION JUST BELOW CLIPPING, 2-4 ohms
Cl 7 (52) missing
NOTE: about 0.1% oscillation right below clipping at 2 ohms is normal.
EXCESSIVE SWITCHING INTERFERENCE.
Switching interference may LOOK like an instability, however it is at a much lower frequency (1lOkH.z) than most instabilities. It will be more visible at low frequencies (2OOHz) and at lower impedances.
Missing jumper at R224.
Missing Cl29, 134 on output board.
Grounds not connected to chassis at output board and front chassis mounting screw.
FEEDBACK PROBLEMS: GAIN INCORRECT
Gain of output stage set by R23, 31 (147, 153)
Gain of Ch 1 volume control buffer stage set by RI 1, 16.
Gain of Ch 2 volume control buffer stage set by Rl37, 139. Make sure Q48 is turned on - grounding RI37 at Q48 should not affect gain. Check RI 32 (drives Q48).
Gain of balanced input is set by 4 matched resistors R9, 8, 12, 13 (129, 130, 135, 136). Confirm both sides of balanced input are working. Check R5, 6 (123, 124).
Gain of output stage set by R23, 31 (147, 153)
Gain of Ch 1 volume control buffer stage set by RI 1, 16.
Gain of Ch 2 volume control buffer stage set by Rl37, 139. Make sure Q48 is turned on - grounding RI37 at Q48 should not affect gain. Check RI 32 (drives Q48).
Gain of balanced input is set by 4 matched resistors R9, 8, 12, 13 (129, 130, 135, 136). Confirm both sides of balanced input are working. Check R5, 6 (123, 124).
Audio Output, Troubleshooting Clipping, Limiting
EXCESS STICKING (TOO MUCH DISTORTION DURING CLIP LIMITING)
Cl4 (49) much too large (also causes increased high frequency distortion).
R38 (161) missing.
R38-39 (161-162) have wrong values.
Q9, 10 (54, 55) missing
R34 (157) or R35 (158) missing
Q8 (53) missing.
Cl4 (49) much too large (also causes increased high frequency distortion).
R38 (161) missing.
R38-39 (161-162) have wrong values.
Q9, 10 (54, 55) missing
R34 (157) or R35 (158) missing
Q8 (53) missing.
CLIP LIMITING DOESN’T WORK:
BOTH CHANNELS:
Check U3 missing,
Check U3 supply voltages, +I 3VCL, -13VCL, on C73* 74
ONLY ONE CHANNEL BAD:
Probe output of U2 (7), pin 7 while clipping. If output exceeds 4V during clipping, check :
R38 (161) missing.
R38-39 (161-162) have wrong values.
Q9, 10 (54, 55) missing.
R34 (157) or R35 (158) missing
Q8 (53) missing
If output at pin 7 clamps at 3.5.4V as expected, check parts surrounding U3:
R32 (154) missing
Q7 (52) missing
R28 (151) missing
Q6 (51) missing
RI8 (141) missing
RI9 (142) missing
SW I:1 (1:lO) not making contact
Check each pin on U3
CLIP LIMITING OSCILLATES:
Cl 3 (48) missing.
R21, 27 (144, 150) missing.
EXCESSIVE STEP DISTORTION (STEP GLITCH)
Close scrutiny of the distortion trace, and scope probing of the switched waveform, will help determine the cause of excess step distortion, The step should switch when the output voltage is within IO-12 volts of its respective rail, This switching margin should be fairly constant from20- 20kHz. The switching event itself should be a fairly uniform up and down ramp, moving at about 25 volts/us, therefore taking about 2us to complete its transition.
Close scrutiny of the distortion trace, and scope probing of the switched waveform, will help determine the cause of excess step distortion, The step should switch when the output voltage is within IO-12 volts of its respective rail, This switching margin should be fairly constant from20- 20kHz. The switching event itself should be a fairly uniform up and down ramp, moving at about 25 volts/us, therefore taking about 2us to complete its transition.
Step Switching Too Close to the Rail:
This will cause increased step glitch, especially at low impedances. If present at all frequencies, check the reference voltages:
Negref: 17.5 volts above its intermediate rail: D88, R276-7-8.
PosRef: 20V below its intermediate rails: D87, R256, 257, D53.
This will cause increased step glitch, especially at low impedances. If present at all frequencies, check the reference voltages:
Negref: 17.5 volts above its intermediate rail: D88, R276-7-8.
PosRef: 20V below its intermediate rails: D87, R256, 257, D53.
Confirm correct values in output voltage divider: R48 loaded by
R49-50 (Rl71, and Rl72-173). If present only at high frequencies, check the
value of the speed up capacitor C20 (C55) in the output voltage divider, or
look for slow switching.
Step Chattering.
If the step repeatedly switches on and off, usually at a low frequency, it creates an oscillation burst which increases step glitch at low frequency. The tendency is usually worse at low impedances and low frequencies. 2-3 “false trials” at very low frequency, 2 ohms, is normal, but prolonged bursts of maximum frequency chattering may cause FET failure.
Positive step: check hysteresis resistor R66 (RI 89)
Negative step: check hysteresis resistor R69 (RI 92) and capacitor Cl 87 (Cl 93).
Slow or Fast Switching.
Slow switching reduces step glitch but puts more strain on the FET. Fast switching increases step glitch. The usable limit is17-27 volts/us, If both slopes are equally off speed, check the slope capacitors:
Positive, C30 (C65) and Negative, C29 (C64).
If only one slope is slow, check the resistors and buffer transistors:
Positive step: R78, 79, Dl5, Q30-31 (R201, 202, D40, Q7576)
Negative step: R83, 84, Dl7, Q32-33 (R206, 207, D42, Q77-78).
If the step repeatedly switches on and off, usually at a low frequency, it creates an oscillation burst which increases step glitch at low frequency. The tendency is usually worse at low impedances and low frequencies. 2-3 “false trials” at very low frequency, 2 ohms, is normal, but prolonged bursts of maximum frequency chattering may cause FET failure.
Positive step: check hysteresis resistor R66 (RI 89)
Negative step: check hysteresis resistor R69 (RI 92) and capacitor Cl 87 (Cl 93).
Slow or Fast Switching.
Slow switching reduces step glitch but puts more strain on the FET. Fast switching increases step glitch. The usable limit is17-27 volts/us, If both slopes are equally off speed, check the slope capacitors:
Positive, C30 (C65) and Negative, C29 (C64).
If only one slope is slow, check the resistors and buffer transistors:
Positive step: R78, 79, Dl5, Q30-31 (R201, 202, D40, Q7576)
Negative step: R83, 84, Dl7, Q32-33 (R206, 207, D42, Q77-78).
Step FET Oscillation.
Certain FET types oscillate at extremely high frequency while ramping up and down. This injects interference into the amplifier which increases the step glitch. Such problems are supposed to be found while (dis)qualifying specific FET types. If they crop up in production, Engineering needs to know.
STEP WON’T TURN ON (Premature Clipping)
If the step refuses to switch high, the amp will clip prematurely, at the intermediate rail, at any load. Make sure the clipping is not acually current cutback, usually evident only at 2 ohms. Probe the output voltage and intermediate rail voltages to confirm clip point and lack of step action. Trace the circuit from the step FET back via gate drive to drive circuit to locate cracks, missing part etc. Check DC power on step driver (14V on EACH positive step drivers, 12V on BOTH negative drivers). Check voltage of PosRef (20V below +65V rail) or Negref (17.5V above -65V rail). Look for severe mismatches of the comparator resistor ladders.
Certain FET types oscillate at extremely high frequency while ramping up and down. This injects interference into the amplifier which increases the step glitch. Such problems are supposed to be found while (dis)qualifying specific FET types. If they crop up in production, Engineering needs to know.
STEP WON’T TURN ON (Premature Clipping)
If the step refuses to switch high, the amp will clip prematurely, at the intermediate rail, at any load. Make sure the clipping is not acually current cutback, usually evident only at 2 ohms. Probe the output voltage and intermediate rail voltages to confirm clip point and lack of step action. Trace the circuit from the step FET back via gate drive to drive circuit to locate cracks, missing part etc. Check DC power on step driver (14V on EACH positive step drivers, 12V on BOTH negative drivers). Check voltage of PosRef (20V below +65V rail) or Negref (17.5V above -65V rail). Look for severe mismatches of the comparator resistor ladders.
STEP STUCK ON (Switched Rail Voltage Stuck On Full)
If the positive step is stuck on, (evidenced by permanent high voltage on switched rail) the FET is probably bad, since the positive gate drive cannot sustain DC turn-on due to the bootstrapping. If the negative step is stuck on, it could be a bad FET, or the gate drive circuit could be holding the FET on, which will easily be confirmed by measuring the gate voltage. Malfunctioning gate drive circuitry should be checked as noted above under “Won’t Turn On”.
REPEATED FET FAILURE.
Repeated failure of step FET’s is usually caused by failure to fully switch ON or OFF (lingering in the linear region). The actual failure usually occurs at 2 ohms, where the dissipation is highest. After replacing the FET, the step waveform should be monitored, starting at light load to avoid repeated failure, and advancing briefly to heavier loads while closely watching the waveform. You will need to use an isolated scope probe which allows voltage readings to be taken with respect to the intermediate rails, or to FET sources.
FET Does Not Fully Turn On:
Generally causes problems at low frequency, 2 ohms.
Confirm that the step FET remains fully on for the entire cycle (2OHz). If not, confirm weak gate drive and determine cause.
Weak positive drive: check voltage on C32 (C51) for 14V. Check C31 (C66), low RIO4 (R227),
missing D18 (Dl48). Check R78, Dl5, Q30 (R201, D40, Q75).
Weak negative drive: check voltage on C67, 12V. Check R83, Dl7, Q32 (R206, D42, Q77).
FET Turns On or Off Very Slowly:
Generally causes problems at high frequency, 2 ohms.
If both slopes are equally slow, check the slope capacitors:
Positive, C30 (035) and Negative, C29 (034).
If only one slope is slow, check the resistors and buffer transistors:
Positive step: R78, 79, Dl5, Q30-31 (R201, 202, D40, Q75-76)
Negative step: R83, 84, Dl7, Q32-33 (R206, 207, D42, Q77-78).
Severe Step Oscillation.
Generally observed at low frequency, low impedance, right at threshold.
Positive step: check hysteresis resistorR66 (RI 89)
Negative step: check hysteresis resistor R69 (RI 92) and capacitor Cl 87 (Cl 93)
Troubleshooting DC Fault Shutdown
NORMAL BEHAVIOR OF THE CIRCUIT.
Any amplifier fault which causes a non-symmetrical output, such as premature clipping of one polarity, a missing step, etc, may trigger DC fault shutdown. This indicates normal operation of the circuit
TRACING THE CAUSE OF FALSE TRIGGERS.
If amplifier is shutting down for no apparent cause, the source of the false signal must be found. Be sure the output is checked with a DC coupled scope in order to confirm absence of an actual DC offset. The circuit will trip on DC offsets exceeding about 4V.
The optocoupler’s input can be safely disabled by shorted Ul5, pins I-2 together. This will indicate if false triggering is before or after Ul5.
The output of UlO:l, pin 1 should be monitored. If it goes low during DC shutdown, it is sending the false signal.
SHUTDOWN OCCURS AS SOON AS SWITCHING STARTS.
Disable Ul5 as noted above, determine if there is a DC fault condition. CAUTION: use 50-ohm resistor in series with AC line to limit fault current in case of shorted outputs.
If amplifier output looks OK, check UlO:l output. If low, check voltage on pins 2 and 3 UlO:l, pin 2: should be zero (no signal)
UlO:l, pin 31 should be about 2V! set by R243, 244, 245.
Check R348 at Ul.5.
SHUTDOWN OCCURS ABOVE ABOUT 4V OUTPUT:
Q87, C7, R240 or D48 missing.
Confirm D48 is pulled low (-13V), holding Q87 on. If not, check RI 17, 118, Q42
NOTE: this control voltage responds to the Br Mono switch, pole 7.
Check R348 at Ul5.
Bad connection at step diodes (D21, D22, D46, D47)
Fan Speed Troubleshooting
FAN STUCK HIGH:
Q88 or Q89 failed
R30 or Rl55, Thermal Sense NTC, shorted to heatsink
R266 or R271 missing.
FAN DOESN’T RUN
Check fan voltage, should be 1 IV when cold, 29V when hot.
Voltage OK -- replace fan.
No Voltage: check Q91, 89, 90, R264 and 265 missing. Confirm that +/-15V is reaching circuit.
Q88 or Q89 failed
R30 or Rl55, Thermal Sense NTC, shorted to heatsink
R266 or R271 missing.
FAN DOESN’T RUN
Check fan voltage, should be 1 IV when cold, 29V when hot.
Voltage OK -- replace fan.
No Voltage: check Q91, 89, 90, R264 and 265 missing. Confirm that +/-15V is reaching circuit.
See the circuit diagram by previous post
QSC PLX 1202 Test Procedure and Circuit Diagram
Testing SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1 - 10 are in the default position (1 on, 10 on, all others off).
3. Connect a distortion analyzer with a resolution of O.Ol%, 20-2OkHz (or better) to the output terminals of the amplifier. Enable the 8OkHz low pass filter.
4. Connect a dual-channel oscilloscope to the following test points:
Chl - a IOX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a IX scope probe (vertical sensitivity - O.lV/cm) to the distortion analyzer output.
5. Set amp gain pots fully clockwise and turn on power switch.
6. Connect the output of the signal generator to the input terminals of the amplifier and select an output of 1.30 VRMS, 1 kHz sine wave.
7. Plug the amplifier into a variac and set up an AC line current monitor.
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1 - 10 are in the default position (1 on, 10 on, all others off).
3. Connect a distortion analyzer with a resolution of O.Ol%, 20-2OkHz (or better) to the output terminals of the amplifier. Enable the 8OkHz low pass filter.
4. Connect a dual-channel oscilloscope to the following test points:
Chl - a IOX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a IX scope probe (vertical sensitivity - O.lV/cm) to the distortion analyzer output.
5. Set amp gain pots fully clockwise and turn on power switch.
6. Connect the output of the signal generator to the input terminals of the amplifier and select an output of 1.30 VRMS, 1 kHz sine wave.
7. Plug the amplifier into a variac and set up an AC line current monitor.
POWER UP 8 MUTE DELAY TEST
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225W resistor (100 ohm, 240VAC) in series with the high (+) lead on the AC cable during variac ramp up. If the switching power supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved stable operation during idle. Remove AC power from the amplifier and disconnect the series resistor for normal operation. Continue with the test & calibration process.
I. Slowly raise the variac voltage and watch for excessive current draw (line current greater than 0.5A a.c. at 60 Volts). This is slightly less for 240V. Pause at 9OVAC (2OOVAC European) for three seconds until the mute I protect circuit disengages.
Continue to 12OVAC (240V European).
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting delay.
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225W resistor (100 ohm, 240VAC) in series with the high (+) lead on the AC cable during variac ramp up. If the switching power supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved stable operation during idle. Remove AC power from the amplifier and disconnect the series resistor for normal operation. Continue with the test & calibration process.
I. Slowly raise the variac voltage and watch for excessive current draw (line current greater than 0.5A a.c. at 60 Volts). This is slightly less for 240V. Pause at 9OVAC (2OOVAC European) for three seconds until the mute I protect circuit disengages.
Continue to 12OVAC (240V European).
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting delay.
CHANNEL OUTPUT
I. Look for amplified signal on the scope for channel 1. Switch the input signal and scope to channel 2 and repeat output test. Check for noisy / contaminated gain pots by observing general instability on the distortion waveform while adjusting the gain control levels.
2. Select an 8 ohm load and confirm that this amplifier is producing 200 watts at 1 kHz just below the point of clipping. Check both channels.
I. Look for amplified signal on the scope for channel 1. Switch the input signal and scope to channel 2 and repeat output test. Check for noisy / contaminated gain pots by observing general instability on the distortion waveform while adjusting the gain control levels.
2. Select an 8 ohm load and confirm that this amplifier is producing 200 watts at 1 kHz just below the point of clipping. Check both channels.
BRIDGE MODE
1. Turn the power switch off.
2. Set Mode Switch #7 in the on position. The gain control, limiter, and filter switch positions on CH2 are disabled with Mode Switch 7 on.
3. Set load to both red output binding posts (CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewave input to channel I of the amplifier. Check the power and verify that the output does not immediately collapse. Check for 700 watts at 8 ohms.
1. Turn the power switch off.
2. Set Mode Switch #7 in the on position. The gain control, limiter, and filter switch positions on CH2 are disabled with Mode Switch 7 on.
3. Set load to both red output binding posts (CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewave input to channel I of the amplifier. Check the power and verify that the output does not immediately collapse. Check for 700 watts at 8 ohms.
5. Turn power off and place the amplifier back into the Stereo
mode with output loads connected to each channel.
Schematic [Circuit Diagram]
BIAS
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of 1.3OVrms increase the input frequency to 2OkHz. Reduce the input signal 20dB (80%) from full output. Adjust the crossover trimpot VR43 (CHl) and VR166 (CH2) for about a 4OOmVpk-pk crossover spike protruding from the noise trace
on the oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion from the amplifier in order to see the crossover spike. It is necessary to disable the 80kHz lowpass filter on the analyzer for this test. Further trim so that the total distortion for that channel is less than 0.1% THD+N.
3. With the trim settings achieved, and with no signal plugged into the amplifier and with an 8 ohm load, verify that the AC idle current from the AC service is no more than 1 .O amperes.
4. Let the amplifier cool down and check channel 2.
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of 1.3OVrms increase the input frequency to 2OkHz. Reduce the input signal 20dB (80%) from full output. Adjust the crossover trimpot VR43 (CHl) and VR166 (CH2) for about a 4OOmVpk-pk crossover spike protruding from the noise trace
on the oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion from the amplifier in order to see the crossover spike. It is necessary to disable the 80kHz lowpass filter on the analyzer for this test. Further trim so that the total distortion for that channel is less than 0.1% THD+N.
3. With the trim settings achieved, and with no signal plugged into the amplifier and with an 8 ohm load, verify that the AC idle current from the AC service is no more than 1 .O amperes.
4. Let the amplifier cool down and check channel 2.
SHORT CIRCUIT CURRENT
1. Select a 2 ohm load and apply a 1.3Vrms sinewave (1 kHz) input signal to both channels of the amplifier. Ensure that power is on and that the gain controls are fully up.
2. While the amplifier is producing power into the loads, apply a short to the output binding posts of each channel. In other words, apply a jumper between the red and black binding posts of each channel. Once this is done, combined AC line current draw for both channels should be no greater than 13A ac. This is with a 120 volt AC service to the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 ohm loads. The output should not experience any hang up and a full sinewave should be present just as it was before a short was applied for this test.
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test.
1. Select a 2 ohm load and apply a 1.3Vrms sinewave (1 kHz) input signal to both channels of the amplifier. Ensure that power is on and that the gain controls are fully up.
2. While the amplifier is producing power into the loads, apply a short to the output binding posts of each channel. In other words, apply a jumper between the red and black binding posts of each channel. Once this is done, combined AC line current draw for both channels should be no greater than 13A ac. This is with a 120 volt AC service to the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 ohm loads. The output should not experience any hang up and a full sinewave should be present just as it was before a short was applied for this test.
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test.
FREQUENCY RESPONSE
1, Set load to 8 ohms and scale the input generator to gain 1 watt of power from the amplifier on each channel. Gain controls on the amplifier should be fully up.
2. Check frequency response from 2OHz to 20kHz (+I- 0.2OdB) by sweeping random frequencies between these extremes. This is done by verifying the same voltage amplitude at each of the frequencies selected (within 2OHz to 2OkHz). Check both channels.
1, Set load to 8 ohms and scale the input generator to gain 1 watt of power from the amplifier on each channel. Gain controls on the amplifier should be fully up.
2. Check frequency response from 2OHz to 20kHz (+I- 0.2OdB) by sweeping random frequencies between these extremes. This is done by verifying the same voltage amplitude at each of the frequencies selected (within 2OHz to 2OkHz). Check both channels.
POWER vs. DISTORTION TEST
I. Check to ensure that both channels will produce rated power at 2OHz, 2KHz, and 20kHz. into an 8 ohm load.
2. While verifying rated power, check that at all frequencies the distortion measurement is less than or equal to 0.03% THD.
I. Check to ensure that both channels will produce rated power at 2OHz, 2KHz, and 20kHz. into an 8 ohm load.
2. While verifying rated power, check that at all frequencies the distortion measurement is less than or equal to 0.03% THD.
THERMAL TEST
1. Set input frequency to 1 KHz and short both channels while they are producing power into a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about 11 - 13.5 amperes for both channels. As the amplifier gets hot, there will be some current drift upwards and the fan speed will increase. This is not a problem as long as the case temperature on the output transistors does not exceed 105 degrees C.
1. Set input frequency to 1 KHz and short both channels while they are producing power into a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about 11 - 13.5 amperes for both channels. As the amplifier gets hot, there will be some current drift upwards and the fan speed will increase. This is not a problem as long as the case temperature on the output transistors does not exceed 105 degrees C.
4. Verify that the NTC circuit causes thermal shutdown after an
extended period.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes.
CM TEST
1. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a 1/4” input jack halfway into each channel and observe about 6 dB of output voltage reduction. There will also be a 180 degree phase inversion at the output of the channel under test.
1. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a 1/4” input jack halfway into each channel and observe about 6 dB of output voltage reduction. There will also be a 180 degree phase inversion at the output of the channel under test.
OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1 kHz 1.3OVrms sinewave input signal. Note the output level at full power just below clipping. Adjust gain if needed.
2. Remove the input signal connector from the amplifier and measure the residual noise level produced into the load by the amplifier. The noise signal should be 107 dB down from the full output power point measured. A signal to noise ratio should be better than
or equal to 107dB. Check both channels.
1. Set the amplifier gain controls all the way up, with a 1 kHz 1.3OVrms sinewave input signal. Note the output level at full power just below clipping. Adjust gain if needed.
2. Remove the input signal connector from the amplifier and measure the residual noise level produced into the load by the amplifier. The noise signal should be 107 dB down from the full output power point measured. A signal to noise ratio should be better than
or equal to 107dB. Check both channels.
FINAL CHECK
This completes the amplifier test procedure for this model. Inspect the amplifier for mechanical defects. Inspect the solder connections. Reassemble the amplifier and verify the amplifier’s operation before returning the product to service.
This completes the amplifier test procedure for this model. Inspect the amplifier for mechanical defects. Inspect the solder connections. Reassemble the amplifier and verify the amplifier’s operation before returning the product to service.
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