Sony KDP-57XBR2 Training Manual page 26

the timer LED flash in sequences of five, which will help steer you in the right direction. A prime example of this
is the failure of Q706, Q733 and Q764 on the CR, CG and CB boards. Figure 6-4 shows the CG board with Q733
as an example. These transistors, which are responsible for monitoring cathode current, would short or leak if
the CRT arced. All three of the transistors are connected to the IK return line via Q734 buffer. If one or more of
these current monitors failed, the IK return line would be "swamped" with DC voltage. IC206 would now be
fooled into thinking that insufficient pulses were being fed back and, depending on how much the current detect
transistor was leaking, would generate a overly bright picture. In some cases, that would cause the set to go into
over-current protect. The best way to isolate this problem is to read the collector voltage of each IK monitoring
transistor. Approximately 2VDC should appear there. If one of the transistors is leaking, you will see 5VDC since
there is a zener diode D736 at Q734B that prevents this line from going any higher. Service Bulletin #443
(E08921862) deals with this issue.
NOTE: This failure can be very confusing. If the unit was not going into protect, you will see video in the bright
raster and notice that OSD was not being displayed either. Since main video and OSD enter the Y/C Jungle IC
at separate inputs, it appears that IC206 is the cause. Many A boards have been be ordered and installed and
the problem would still exist. It is important to remember that on all Sony televisions, the OSD will not function
until the unit has completed all initialization routines and this includes the AKB circuit.
If the video level problem is not AKB related (timer LED not flashing), you will have to try to eliminate IC206 as the
cause. Again, OSD is a valuable tool. If it is of the correct level, IC206 is probably not the cause. Try using PIP
to see if the sub video level is OK. If it is, troubleshoot the main video path. If both sub and main video are too
high or low, check the voltage at pin 28 of IC206. This is the ABL input and the voltage will fluctuate between 2
and 6VDC with 2V on a bright scene and 6V with no video. The ABL line from a flyback transformer is negative
going and pull up resistors from the 135V supply will be used to keep it at a positive level. These pull up resistors
are known to increase in value and cause the line to go low or even negative. IC206 will react by lowering
brightness significantly since it is trying to protect the flyback transformer.
FSC OUT FROM IC206/57
TO J1105 MONITOR OUT
YUV MUTE FROM Q1110
FROM MAIN TUNER
FROM J1102
FROM CN1702/5
FROM J1101
FROM SUB TUNER
S VIDEO
INPUTS
COMPONENT Y
S VIDEO
INPUTS
SDA
SCL
MTV V
63
41
Q1103, 1104
MAIN V
8
BUFFER
OUT
V1
1
V2
15
V3
60
STV V6
YOUT2
10
39
Y1
3
YIN2
Y2
17
45
Y3
24
Y4
C1
12
CIN2
43
C2
15
37
C3
19
COUT2
TO IC1903/1YUV SWITCH/DYIN, IC1902/34 SUB DECODER/YIN
AND IC1602SUB V CHIP
SYOUT
56
34
58
SCOUT
IC1101
35
AV SWITCH
CXA2079Q
FIGURE 6-2 - SWITCHING AND COMB FILTER (S MODELS)
6. RA-3/3A Video Process Troubleshooting: T & S Models
CV
Q1701, FL1701
Q1702, Q1703
Q1102 Q1704, FL1702
Q1707, Q1708
BUFFER
MAIN Y TO IC1901/19 & 23 YUV
CONTROLLER/TVIN+DVD Y
MAIN C TO IC206/64 YCJ/CIN
TO IC1902/30 SUB DECODER/CIN
23
11 CKIN
IC1702
COMB FILTER
TC90A53F
ADIN
41
COUT
YOUT
23 25
Q1705, FL1703
Q1706, Q1709
6.2TVP14 5/22/02