93
20. RA-5A Chassis Protection Block
Testing – Unplug CN7001 to the Q box (consists of QI and QM boards) and power On the TV. Normally the TV will
power ON with HV, a dark screen and no sound because there is no microprocessor-to-microprocessor commu-
nications. If the TV does not shut down, the problem is in the Q box because you unplugged the short. If the TV
still shuts down, the problem is in the primary power supply (G board). Measure “Sub 6.5Vdc” at D6130 cathode
on the G board at power ON. A high of 8Vdc will trip the protection latch and shut down the TV. The TV will not
display A/V without the Q boards active, but will remain ON.
Standby light blinks seven times – TV Shutdown
Refer to Figure 20-11 for the circuit and testing of the Horizontal sweep detection circuit.
Circuit – If the horizontal sweep is lost for a moment, three vertical lines would instantly appear on the three CRTs
and burn a line into the tubes. To prevent this, a horizontal activity circuit consisting of D3011, C3090, R3140 and
Q3037 keep IC3006/pin 34 LOW as long as horizontal pulses are fed into the circuit.
Horizontal pulses into the activity circuit come from the horizontal Output transistor Q8024/Collector. A capacitor
voltage divider (C8096-8) reduces the 1KV, 31.5kHz spikes. The horizontal spikes are clamped (limited) and
shaped into rectangular pulses by zener D8026. Buffers Q8031/Q8101 apply the reshaped pulse to the horizon-
tal activity circuit. D3011 is the first part of this circuit outputting a DC voltage to LPF C3090/R3140. The DC
voltage keeps Q3037 turned ON. When Q3037 is ON, IC3006/pin 34 remains LOW for normal operation.
During a defect when horizontal pulses are NOT detected, IC3006/pin 34 goes HIGH. This HIGH is used to blank
the screen, trigger the Standby LED indicator and shut down the TV. IC3006 blanks the RGB output in its own IC
and sends data to instruct Main Micro IC001 to blink the standby LED seven times. The HIGH is also applied
through D3009 to the latch circuit on the G board to shut down the TV for safety.
The protect Mute line from IC001/pin 67 places a HIGH at Q3037/base for five seconds at power ON to prevent
this circuit from shutting the TV back off after turn ON.
IC001
MAIN
MICRO
IC6002,
T6004
PRIMARY
P.S
9
8
1
2
C24
43
50
SURGE
RELAY
RY6002
R6175
D6130
D6144
D6133
7.5V
R6180
1k
C6194
4.7
R6178
47k
R6184
100
D6132
LOW
6.2
PROT.
P
Q6110
R6183
R6182
10k
Q6111
CN3020/
CN001
CN6101/
CN3016
L6102
Q6115
R6174
CN3015
CN7001
CN6104/
CN3104
SUB
6.5V
SOURCE
STBY
LED
(HA BD.)
B BD.
G BD.
A BD.
QM BD.
P
N
STBY
5V
32TVP12 1349
0.1VDC
8
FIGURE 20-10 - PROTECTION - 6X INDICATION - RA-5A CHASSIS
69
AC RELAY
Summary of Contents for KD-34XBR2 - 34" Hdtv Fd Trinitron Wega
Page 77: ...74 RA 5A Chassis Board Layout ...
Page 108: ...APPENDIX ...
