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10. RA-4/4A Deflection Circuit Troubleshooting
Vertical Deflection Troubleshooting
No Vertical Deflection: The first instinct of the technician is to go after the vertical output IC1501 and understandably
so. It is a drive component with heavy current usage and heat dissipation, and it is usually the cause of the
failure. It is amazing how many techs change this IC first without doing a few checks. What should you do now
that the new IC has not cured the problem?
The first check that you should perform (and this applies to all Sony televisions of the last seven years) is to
check the voltage level of the clock and data lines on the I
2
C bus. They are conveniently labeled SCLK and
SDAT. The DC voltage should not be lower than 4.6 volts. If either of these lines is loaded down, the vertical
oscillator will not start. This is the number one cause of multiple component replacement for a simple vertical
problem. You should always check the clock and data level whenever you have a strange problem, particularly
if it appears that you more than one problem. Although most television chassis’ will not produce vertical deflection,
some will generate other symptoms. As an example: The AA-2W used in Sony’s KV32/36XBR200 sets provides
a magenta raster with no video and insufficient vertical height. Assuming the bus is okay, move onto the next
scenario:
Check for V drive at IC5004/pin 1. Since this unit shuts down during a vertical failure, you will have to override by
shorting Q5005 E-C.
Unplug all three CRT sockets when doing this.
It is obvious why this unit shuts down
during a vertical failure. If the sawtooth signal is getting to IC5004, the problem is in the output stage. If not,
work your way back to IC512 and its associated circuits. Assuming the +15V and –15V supply rails are present,
you are only left with a bad driver IC, open yoke or open connection to the yoke. The V protect circuit could also
be engaging due to a failure there. If the sawtooth signal is not present, work your way back to IC512 and its
associated circuits.
Repeat Vertical Output IC Failure: If IC1509 fails immediately upon replacement or soon thereafter; it is usually
the fault of C5037. 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 or it has a problem and
is unable to comply. Due to the nature of the operational amp within IC1509, it is rare for it to be the cause.
Operational amps have massive amounts of gain, which is why they need negative feedback to keep them under
control. Gain problems are most likely to be caused by improper supply voltage (very rare) or problems in the
feedback line. 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 (R5067 or R5071). What should normally
be here is approximately 1VPP of vertical rate sawtooth. If there is a problem here, 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 TH1501 has opened.
The negative feedback of the op amp 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 and low-pass filtering is needed. Suspect an open C5028 at this point.
Should the feedback line check OK, you now have a possible input problem. IC 512 can cause this and it is
difficult to verify without replacing it. Before changing IC512, try one more thing: Replace the EEPROM, IC1007
on the A board. It has caused this symptom. It is less expensive and only has eight legs.
