Posted By
TLC
on 2021-07-14
05:24:19
|  Re: Commodore 16: Black and white screen on Composite, color on the RF
@Retroshire: according to the schematics, this is a 40pF trimmer. I think this can only be tested by desoldering and measuring by a multimeter (with one that is capable of measuring capacitance in the pF range). Alternatively, one could desolder the trimmer and replace it (temporarily) with one of a similar range (and test whether adjustment results in some effect now).
BTW, when you made the tests over the RF connection, did adjusting the trimmer have (similarly) no effect? (I.e. did the colours remain, whatever the trimmer's setting?) That really either suggests some problem in the oscillator circuit, or, the fact that the display indeed tolerates colour subcarrier variances very generously in RF mode (maybe both). If you check the oscillator circuit (by simply inspecting the components, the solder joints, maybe checking the connectivities by a multimeter, against the schematics), can you see anything "suspicious" there?
(A small note - the fact that the trimmer can be turned around without limits, by itself, is normal.)
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