79
18. RA-5A Deflection Circuit Troubleshooting
IC5004
V OUT
LA78045
B19
A20
IC3006
VIDEO
PROCESSOR
CXA2150AQ
25
24
52 53
7
1
2
4
35
5
+15V
-15V
FROM
SEC
P.S
(G BD.)
R055
S DATA
R069
STBY LED
AC RELAY
(B BD.)
S CLK
CN013/
CN3022
+
- V
DRIVE
V PROTECT
CN3005/
CN8006
CN3103/
CN5505
3
5
7
FIGURE 18-2 - VERTICAL DEFLECTION RA-5A CHASSIS
B
G
R
R8040
220
Q8001
BUFF.
R8036
R8039
2.2
D8001
5.6V
R8015
V DY
CN8009
CN8008
CN8007
3
1
3
1
3
1
18.2TVP14 1462
B BOARD
A BOARD
IC001
MAIN MICRO
M306V2MF
26
31
D BOARD
Repeat Vertical Output IC Failure: If IC1509 fails immediately upon replacement or soon thereafter; it is usually
the fault of C8015. This is the boost capacitor. It charges to almost 30VDC during the lower half of the vertical
sweep to provide additional voltage to allow the beam to retrace to the top rapidly. When this filter dries out or
opens, the output IC will attempt to accomplish the retrace but the negative feedback line will resist the sudden
voltage kickback from the yoke and the +15V drive will cause the IC to draw excessive current. In smaller
televisions, a boost capacitor failure causes slight loss of vertical at the top with some fold-over.
Insufficient Vertical Height: Either the vertical output IC is being told what height to display and is unable to
comply, or it is receiving erroneous drive information. Due to the nature of the operational amp within IC5004, it
is rare for it to not be able to amplify properly. Operational amps have massive amounts of gain, which is why
they need negative feedback to keep them under control. Suspect IC5004 as the last possible cause. Gain
problems can be caused by improper supply voltage (very rare) or problems in the feedback line (more likely).
This is why you should always scope the feedback line when height or linearity problems arise. In this chassis,
the best point is the top end of the ground return resistors (R8036 or R8039). What should normally be here is
approximately 1VPP of vertical rate sawtooth. If there is a problem, you will observe one of two things: A
significantly larger sawtooth level or horizontal frequency contamination in the sawtooth. A large sawtooth indicates
one or more of the ground return resistors or the thermal compensator TH8001 has opened. The negative
feedback of the operational amplifier will respond by reducing gain. If there is a large amount of horizontal
component in the feedback, the amp will also reduce gain since the average DC level will be higher at this
frequency. The vertical deflection yoke windings are right next to the horizontal windings so it is very easy to
induce this into the vertical return. Suspect an open C8001 or C8023 at this point.
Should the feedback line check OK, you now have a possible input problem. IC3006 can cause this and it is
difficult to verify without replacing it. Beware that faulty NVM ICs have been known to cause vertical height
problems.