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20. RA-5A Chassis Protection Block
135V Current Sensing Circuit (G board)
The 135V sensing circuit consists of R6118 and IC6102. R6118 is connected to the 135V line at the ground end.
As the current along the 135V line increases, the voltage across R6118 becomes negative (similar to ABL volt-
age). This negative voltage that represents the 135V-line current offsets the 0.27V at comparator IC6102/pin 2.
When the voltage at IC6102/pin 2 drops to the same voltage as pin 3 (0V), the output pin 1 goes HIGH to shut
down the TV and light the standby light.
The HIGH from comparator IC6102/pin 1 is split into two paths. One path is through D6124 to trip the Q6105/
Q6119 latch that shuts off the TV. The other path is through CN6101/pin 6 to inform the Main Micro IC001 that the
135V line current has exceeded 0.7A. IC001 will indicate the 2X-blink failure code as long as the TV is plugged
in.
Testing – You can determine if the sensing circuit or the load is defective by removing the load, but you must keep
the error regulating circuit on the G board operational. L6106 is in series with the 135V output connector CN6106/
pin 9. Removing L6106 removes all the loads. You should then power up the TV to see if the standby LED still
blinks two times. It will usually stop blinking two times, meaning you disconnected the problem but the TV will still
shut down and blink seven times because there are no H pulses.
The problem has been isolated to load on either the D, C, A or V boards. See Figure 20-7. The +135Vdc leaves
the G board and goes to the H. Regulator and Output stage load on the D board and the velocity modulation coils
on the V board. Attack the D board first by testing the H Out transistor (Q8024), and the H Regulator output
transistor (Q8027). A similar circuit description and simplified schematic of an H. Regulator and Output stage is
in the DTV-02 training manual on page 37. The V board can be unplugged and the zener on the A board could not
cause the TV to enter shutdown. Reinstall L6106 onto the G board.
If the LED still blinks 2X with the load disconnected (L6106 removed), the problem is on the G board sensing
circuits. Suspect IC6102, IC6103 and R6118.
Standby light blinks three times – TV Shutdown
Refer to Figure 20-7, for the following 135V OVP circuit explanation and testing.
Circuit –The +135 voltage limit is 150Vdc. This limit is checked by R6101, R6102 and IC6102. Normally with an
output of 135V, the junction of the R6101/R6102 voltage divider produces 2.3Vdc into IC6102/pin 5. This 2.3V is
compared to the 2.5Vdc reference voltage placed at pin 6 by IC6103. Because the 2.3Vdc applied to the + input
of Op Amp IC6102/pin 5 is lower than its input at pin 6, the output at IC6102/pin 7 will be 0Vdc. However, if the
135V line rises to 150Vdc, its corresponding voltage at IC6102/pin 5 will increase from 2.3V to meet the reference
voltage of 2.5V. IC6102’s output at pin 7 will go HIGH. The HIGH that outputs IC6102/pin 7 is applied to the
Q6105/Q6119 latch that shuts off the TV set. The HIGH also goes to IC001 via CN6101/pin 7 causing the standby
LED to blink three times repeatedly.
Testing - To verify the defective condition on the G board, monitor the 135V line at CN6106/pin 9. If this line rises
above 135V at turn ON, the secondary power supply or its regulator (G board) is at fault.
If the 135V line did not rise above the limit, this 135V OVP sensing circuit is defective. Measure the shutdown
latch trip voltage at CN6101/pin 7. At power ON this voltage normally remains at 0Vdc. If this line rises above
0.7Vdc, then suspect IC6102 and IC6103. All these circuits are on the G board.
Standby light blinks four times – TV Shutdown
Refer to
Figure 20-8
for this circuit description and testing.
Circuit - A Vertical Output IC failure or secondary power supply failure (both on the D board) will stop vertical
pulses from being detected at IC3006/pin 35. This loss will cause IC3006 to blank the screen (no RGB output)
and emergency serial data will be sent to Main Micro IC001 (B board). IC001 turns the TV OFF by dropping the
AC relay drive voltage (IC001/pin 69 goes LOW) and blinks the LED four times.
Содержание KD-34XBR2 - 34" Hdtv Fd Trinitron Wega
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