A dormant intermittent problem is difficult to detect. The
BA-4 chassis Control Tuning System IC001 has a program to record the number of times
the TV has failed in the first three categories listed above. This information
can be accessed and displayed on the TV screen as long as the set remains
plugged in.
SELF DIAGNOSTIC ACCESS
With the set OFF, aim the remote at the TV and press the
following remote buttons in this sequence:
1. Display
2. 5
3. Volume Down [ – ]
4. Power On.
The TV will power ON and display the self-diagnostic page.
This self-diagnostic display will overlay the TV or video picture.
At the left of the self-diagnostic TV screen display are the
numbers 2, 4 and 5. These represent the number of times the Timer/Standby light
was blinking. The numbers 3 and 101 are not used (N/A). The column on the right side shows the
number of failures that have occurred since the program was reset. Up to 99
failures can be recorded. Although the
self-diagnostic page will display the number of times a failure has occurred,
it will not be able to tell you exactly where the problem is, only that it
exists.
Self-Diagnostic is new in the series BA-4 TV chassis. It
uses a blinking light or OSD to notify you if there is a failure caused by the
following:
1. Excessive fly-back current or amplitude;
2. No Vertical sweep; or
3. No green automatic white balancing signal.
TIMER/STANDBY LIGHT
The number of times the Timer/Standby light blinks indicates
what failure the Control Tuning System Microprocessor IC001 detects. IC001 will
shut off or blank the TV set to protect itself. The Standby/Timer light will
continue to blink as long as the TV is plugged into AC power.
The number of times the TV has failed is held in memory. As
long as there is failure information present, the standby light will blink when
the set is tuned OFF. Unplugging the TV
set will clear the memory information and stop the blinking.
FAILURE CHECK LIST
Some of the reasons for the failure could be in this
checklist.
When the problem is intermittent, you will have to probe
further by monitoring the horizontal output transistor temperature and the TV’s
current consumption to see if it is high, vibrate and possibly “bake” the set
to force the intermittent failure to reveal itself.
MEMORY CLEAR
Unplugging the TV from AC power resets the stored failure
information and stops the blinking light. The memory is cleared once standby
+5Vdc is removed from the Control Tuning System Microprocessor IC001. It can
also be manually cleared by first pressing 8 and then pressing ENTER while you
are in the self-diagnostic mode.
- Unplug the TV from AC. à Removing AC power clears the memory at any time.
- From the remote control. à Press buttons: 8,then press ENTER.
Self Diagnostic Exit:
Shutting off power to the set retains the memory information
and allows you to return to the TV picture.
SELF DIAGNOSTIC CIRCUIT
The self-diagnostic program is contained in the Control
Tuning System IC001. The number of problems is detected by the program is
stored in IC001. This number remains in IC001’s resident memory as long as the TV
remains plugged into AC and is not manually cleared.
When the TV set is turned ON, IC001 monitors three TV
conditions using two inputs at pins 37 and 17. These TV conditions are:
1. Vertical Failure - In normal operation, Vertical Output
IC541’s “Ref” pin 3 outputs a 30Vp-p pulse (1msec pulse width). This voltage is
reduced by R549 and clamped to no higher than 5Vp-p by D001. These vertical pulses from IC541/pin 3 are
monitored by Control Tuning System IC001 at pin 17. A vertical drive failure causes no pulses to be generated. If
these vertical pulses are lost for two seconds, IC001 will turn OFF the TV to prevent
the vertical deflection failure from damaging the CRT. However, the front panel
Timer/Standby light continues to blink four times, pauses and repeats, even
though the set is OFF.
2. Excessive Current Demand/Excessive FBT pulse
amplitude – Y/C Jungle IC301 monitors both of these conditions at input pin 18.
Normally there are horizontal pulses applied to IC301/pin 18 when the TV is ON. When there is excessive current being drawn
by the FBT or Horizontal Output Transistor, the horizontal pulses are grounded
out. The Y/C Jungle IC301 detects this loss from pin 18 almost immediately and sends
data from IC301/pin 35 to IC001/pin 37 (even in normal operation, there is
always data on this line). IC001 shuts OFF the TV to protect itself. The Timer/Standby light blinks two times,
pauses and repeats to indicate the failure.
If flyback (FBT) pulses were abnormally high, perhaps as a result of an
open resonate capacitor (C508 in this set), the TV would similarly shut down.
Higher than normal FBT pulses result in a high DC voltage that also grounds the
horizontal pulses at IC301/pin 18. The loss of horizontal pulses is detected
and data is sent from IC301/pin 35 to IC001/pin 37 for the TV to shut OFF. The
Timer/Standby light continues to blink two times, pauses and repeats after the
failure.
3. White Balance Failure – Jungle IC301 initiates CRT drive
and monitors CRT cathode current at pin 21. The amplitude of the three IK pulses
that return to IC301/pin 21 represent the level of red, green and blue CRT
cathode emissions. Their amplitudes are used to white balance the picture while
the TV is ON.
This IK circuit is designed to look for three IK
pulses returned from the picture tube. If IC301 detects a missing IK pulse
within two seconds after the set is turned ON, the video is blanked (muted).
The two seconds allow time for the picture tube to warm up. This blanking state
is relayed as data from IC301/pin 35 to C001/pin 37. IC001 causes the
Timer/Standby light to blink five times, pause and repeat. The set remains ON
during this video failure, so the sound is still present.
When there are multiple failures, the two blinking light
failure has a higher priority over the four blinking light failure. By the same
logic, the four blinking light failure has a greater priority than the five
blinking light failure. For example, if multiple failures caused all of the
two, four and five blinking light failures to be stored in memory, the
Timer/Standby light would blink two times, pause and repeat when the TV shut
down. The number of failures has nothing to do with how many times the light
blinks.
Display
By using the TV’s remote control, you can access this
failure information stored in memory. Once IC001 receives the self-diagnostic
access command at pin 12, IC001 powers ON the TV. The failure information from
IC001 is sent to the Jungle IC301 as On Screen Display (OSD) video levels. A “OSD Blk” signal accompanies the OSD video
levels from IC001 into IC301. This analog input voltage at Jungle IC301/pin 29
is used to darken (blank) the main RGB picture signal at the instant the OSD
character is to appear and enable the OSD. Since IC301/pin 29 is an analog
input, 0Vdc input leaves the main picture at normal brightness. 2Vdc input reduces
the picture to half brightness and 5Vdc blanks or mutes the picture.
While the main picture is at half brightness, the OSD
self-diagnostic page is displayed at normal brightness and appears as an
overlay to the main picture.
