Posted By
TLC
on 2021-07-14
08:34:19
|  Re: Commodore 16: Black and white screen on Composite, color on the RF
@Retroshire: so far I thought, that only NTSC models were equipped with an RF modulator that had a channel switch (...plus the Argentinean PAL-N machines i.e. the Drean Commodore 16, that were built using stock NTSC motherboards with modifications). Honestly, I haven't seen a PAL 264 series machine with a channel switch equipped modulator yet. The machines I've seen look like this or this, and an NTSC modulator equipped one looks like this (minus hack, see switch beside the RF out socket). Doesn't your machine happen to have some kind of "special" origin, record, relevant info, ...whatever?...
To answer your question - on NTSC models, the channel switch selects the RF channel to be used (System M channel #3 or #4, VHF). The TV should be re-tuned once the switch is turned to the other position. I don't know what this kind of switch should be doing on a PAL model. All ones I could see so far, used channel #36 (System G, UHF) exclusively, and there was no switch. (There is in fact a small switch inside the PAL modulator accessible from the top, which only affects the sound modulator's carrier frequency).
The difference found between the average AC voltages of a working / this machine in question, is interesting. That's the first indication (provided that all other circumstances are identical), that this machine does something measurably "differently" to a reference model.
Ps. may be a trivial one, but, could you possibly verify, that the machine's main oscillator has a 17.73447MHz crystal?
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