Posted By
TLC
on 2021-07-15
07:02:38
|  Re: Commodore 16: Black and white screen on Composite, color on the RF
@Retroshire yes, this is frustrating indeed. However, I'd say fixing something is always a matter of available options vs. the problem to be solved. High frequency electronics are generally difficult to diag (except for trivial or maybe moderately complicated cases) without proper equipment i.e. an oscilloscope and schematics. If one followed a systematic approach, (s)he'd check signal shapes over the signal path (from the endpoint backwards, at several points), maybe compare the results to a known to working reference if there's one, and draw conclusions from that. Also, the RF modulator is somewhat particularly difficult to diag (compared to the rest of the mainboard), because of its structure (as, there are few chances to even measure things without desoldering the box... there are SMD parts mounted on the bottom side) and because it's an analog high frequency circuit. So, my answer is, if you can get hold of an oscilloscope (can be an expensive call), then you can likely obtain more clues, and eventually find the root cause (which may or may not be easy to fix, a different matter). It's also possible to systematically replace parts with known to working ones - can be a desperate strategy as we all know  , and may eventually also lead to results. Sorry, I have no more ideas  .
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