Currently trying to iron out a smearing issue that appears on high contrast areas, especially text. I believe this in not an uncommon problem, but I've tediously made several attempts to trace the cause with no success so far. I understand this is typically due to problems with open coils or leaky caps in the IF and Video stages...
Example 1:
Example 2:
Some test info and findings:
- CRT tests good on emissions, about 1/3 into the good scale on a B&K 465. I don't recall what the cutoff was, but the picture is bright and clear
- All tubes in IF section test good and have no shorts and aren't gassy
- Performed step one in RCA service guide for peaking (max/min) IF stages with non sweeping frequency and this did NOT affect or remedy the smearing. I assume this stage of alignment is to get your stages "in the ballpark" before further refinement in the sweep gen alignment procedure?
- Injected composite video into circuit, just before the 1st Video Amp, and observed smearing, leading me to believe the defective component should be after that stage.
- Injected composite video into circuit, just before the 2nd Video Amp, and observed a reversed fainter image, but didn't notice smearing - not that there couldn't have been any, I just didn't see it, leading me to believe offending component to be before this stage.
- All peaking coils' in IF and Video tested ok in terms of resistance, cold solder joints. Adjoining resistors were also tested - a couple were out of tolerance and replaced, but did not affect the smearing.
- Replaced the video detector diode - no effect.
- Replaced coupling caps in these sections - no effect.
- Switched the converter box - no effect.
- Tested continuity and resistance of Delay Line and noted about 130Ω. Even shorted the delay line to see color shift but no change to the smear.
- Saw no cold solder joints on the underside of the IF or Chroma boards.
IF section Sams schematic:
Pt 1
Pt 2
Thoughts/questions
- One thing that I observed was that when I jumped a couple of the peaking coils there was no effect to the picture. Could this mean that there might be shorted turns in one or more of the coils? I don't have an LCR meter, but I do have a Sencore YF-33 Ringer Yoke FLyback Tester. Not sure yet how to use that to test peaking coils.
- Adjusting coils, traps or transformers in the IF/Video stages doesn't affect the smearing
- Could it be poor cutoff on the CRT? The CRT is bright and clear though.
05-23-2021, 12:38 PM
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