ST-BY POWER SUPPLY CIRCUIT
Shut
down occurs when the shutdown SCR QP01 is activated by gate voltage. When QP01
receives gate voltage of 0.6V, the SCR fires and give a ground path for the pin
(5) of Connector PQD2 called PROTECT. This Low is routed to the Sub Power
Supply PWB and is impressed on the base of the Relay Driver Transistor Q911
turning it Off. When Q911 turns Off the Relay S901 will disengage and remove
the AC source from the Deflection Power Supply.
VOLTAGE
LOSS DETECTION
1.
Shorted 220V (DP31 and DP32) Inverted by QP03 then through DP22 The cathode of
DP31 is connected directly to the 220V line. If it shorts this circuit is
activated and pulls the base of QP03 low. This output High is routed through
DP22 to the gate of the Shut Down SCR QP01.
2.
Shorted SW+8V (DP33) Inverted by QP03 then through DP22 The cathode of DP33 is
connected directly to the SW+8V line. If it shorts this circuit is activated
and pulls the base of QP03 low. This output High is routed through DP22 to the
gate of the Shut Down SCR QP01.
3.
Shorted 28V (DP30) Inverted by QP03 then through DP22 The cathode of DP30 is
connected directly to the 28V
line. If it shorts this circuit is activated and pulls the base of QP03 low.
This output High is routed through DP22 to the gate of the Shut Down SCR QP01.
4.
Shorted Side Pin Cushion Circuit (D760 and Q754) then through DP34 The Side Pin
Cushion circuit is comprised of I651, Q652 through Q657 If a problem occurred
in this circuit that creates a Low on the cathode of D760, the low will be
routed to the base of Q754, turning it
Off.
This output High is routed through DP34 to the gate of the Shut Down SCR QP01.
5.
Shorted Deflection Transformer or Misoperation (D756 and Q754) then through
DP34 The Deflection circuit generates the actual Drive signal used in the High
Voltage section. If a problem occurs in this circuit, the CRTs could be damaged
or burnt. D757 is connected to D759 which is normally rectifying pulses off the
Deflection Transformer T753. This rectified voltage is normally sent through
D757, D756 to the base of Q754 keeping it On and it’s collector Low. If the
Deflection circuit fails to produce the pulses for rectification, the base
voltage of Q754 disappears and the transistor turns Off generating a High on
its collector. This output High is routed through DP34 to the gate of the Shut
Down SCR QP01.
6.
Heater Loss Detection (DH26, DH27,QH07 and DP34). This voltage does not go to the CRTs.The Flyback Transformer TH01
generates a pulse called Heater. (Note: This does not go to the CRTs as heater
voltage, it’s used for Excessive High Voltage Detection. If a problem occurs
in
this circuit, the Excessive High Voltage Detection circuit wouldn’t operate. It
would be possible for there to be High Voltage but the circuit detecting
Excessive High Voltage couldn’t work. DH26 is connected to DH24 which is
normally rectifying pulses off the Flyback Transformer TH01. This rectified
voltage is normally sent through DH26, DH27 to the base of QH07 keeping it On
and its collector Low. If the Heater Pulse fails to produce the pulses for
rectification, the base voltage of Q754 disappears and the transistor turns Off
generating a High on its collector. This output High is routed through DH30 to
the anode of DP34 to the gate of the Shut Down SCR QP01.
NEGATIVE
VOLTAGE LOSS DETECTION:
7.
-M28V Loss Detection (DP23, DP24) RP31 (18K ohm) is connected to the negative
–M28V line and RP30 (22Kohm) is connected to the positive +29V line. The
Cathode of DP23 monitors the neutral point where these two resistors are
connected. If the negative voltage disappears, the zener DP23 fires. This high
is routed through DP24 to the gate of the Shut Down SCR QP01 and Shut Down
occurs.
8.
SW-8V Loss Detection (DP28, DP29) RP26 (3.3K ohm) is connected to the negative
SW-8V line and RP25 (3.3Kohm) is connected to the positive SW+8V line. The
Cathode of DP28 monitors the neutral point where these two resistors are
connected. If the negative voltage disappears, the zener DP28 fires. This high
is routed through DP29 to the gate of the Shut Down SCR QP01 and Shut Down
occurs.
EXCESSIVE
CURRENT DETECTION:
9.
120V Deflection Power Supply (RP17, QP02, DP15, DP16 and DP18) If an excessive
current condition of the Deflection B+ is detected by RP17 a 0.47 ohm resistor,
the base of QP02 would drop. This would turn on QP02 and the high produced at
the collector would fire zener DP15. This High would be routed through DP16
through DP18 to the gate of the Shut Down SCR QP01 and Shut Down occurs.
10.
28V Vertical IC I601 Power Supply (R645, Q609, D615, and DP34) If an excessive
current condition of the Vertical B+ is detected by R645 a 0.68 ohm resistor,
the base of Q609 would drop. This would turn on Q609 and the high produced at
the collector would be routed through D615 through DP34 to the gate of the Shut
Down SCR QP01 and Shut Down occurs.
VOLTAGE
TOO HIGH DETECTION:
11.
Excessive High Voltage Detection (DH31, RH54, RH55 and DH24). Sensed from the
Heater Voltage generated from pin (5) of the Flyback Transformer TH01. Also,
(DH42) sends a high command to the Horizontal Driver IC IH02, to defeat
Horizontal Drive Output The Flyback
Transformer
TH01 generates a pulse called Heater. (Note: This does not go to the CRTs as
heater voltage, its used for Excessive High Voltage Detection). If this voltage
goes too high indicating an excessive High Voltage condition, the voltage
divider comprised of RH54 and RH55 would impress a high on the cathode of DH31. This high is routed through DH34 to the gate
of the Shut Down SCR QP01 and a Shut Down occurs.
12.
Side Pincushion failure generating a High. (D754, and D753) The Side Pin
Cushion circuit is comprised of I651, Q652 through Q657 If a problem occurred
in this circuit that creates a High on the cathode of D754, the High will be
routed through D753 to the gate of the Shut Down SCR QP01.
13.
Deflection B+ Too High. (DP17, RP21 and RP22 RP21 and RP22 form a voltage
divider. The top side of RP22 is monitored by DP17. If this voltage goes too
high, zener DP17 will fire. This high is routed through DP18 to the gate of the
Shut Down SCR QP01 and Shut Down
occurs.
14.
Heater Voltage from the Deflection Power Supply Too High Detection. (DP27 and
DP28) The Heater Voltage for the CRTs filament is generated in the Deflection
Power Supply. This voltage is monitored by DP27. If this voltage goes too high,
zener DP27 will fire. This high is routed
through DP28 to the gate of the Shut Down SCR QP01 and Shut Down occurs.
