Sony KV-13FS100 Product & Training Manual page 34

6. Video/RGB
If there is a defective cathode, the voltage at that cathode will be less then 130V. For the extreme case of an
open cathode, the voltage will be 116V. The other good cathode voltages will be normal at 150V. What's
happening is the IK-AKB circuit is trying to compensate for the defective cathode by driving it harder (116V) then
the other cathodes (150V). If this voltage variation appears on one or more cathodes, suspect a defective
cathode, and thus a defective tube.
Also, check the IK Feedback pulse at IC545/pin 5 (ref. Waveform 6-7) one pulse will be completely missing.
Failure: One or more of the IK Drive pulses is not output from IC001/pins 31, 33 and 35 to the CRT.
Circuit Operation: The video (color bars) will appear on the picture tube with one or more colors missing.
Check for the Video and IK Drive Pulses at IC001/pins 31, 33, 35 Video and pulses should appear as shown in
Waveform 6-6. Most likely, the output will be completely missing Video and IK Drive Pulses. A defective IC001
or Open in path from IC001 to IC1751 to the CRT can be confirmed by checking the voltages on each cathode
(CV board). The voltages on the good cathodes with drive will be normal at 150V; the cathode with no drive pulse
will be ~175V.
Failure: The IK Feedback pulses are not returned to IC001/pin 51 from IC1751/pin 5 (open return path or
defective IC1751).
Circuit Operation: The video (color bars) will appear washed-out on the picture tube (bright white halo throughout
picture). If IC001/pin 51 does not receive the IK Feedback pulses from IC1751/pin 5, then IC001 will detect three
defective cathodes. The voltage measured at each cathode will be 120V. IC001/pins 31, 33 and 35 will output
maximum signal level in an attempt to compensate (ref. Waveform 6-6). Check IC1751/pin 5 for IK Feedback
Pulses (ref. Waveform 6-7). If these pulses are missing, suspect defective IC1751. If the pulses are present,
trace pulses to IC001/pin 51 to find open circuit.
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