after solving the DIN problem I started building the second SID module for my synth.
1 Core r4d
1 Sid r3d (with 8580chip) and 2200uF electrolytic cap
optimized c64 psu
Due to some soldering paste left on the board when I connected the board to test voltages I got some smoke and sparkles between the voltage regulator and c10(330nF). I cleaned the board and replaced them.
Voltages on SID module are 8,9V at the voltage regulator output and 5,15V from Core module
Now, I’m getting a lot of noise, with or without the 8580.
Probably something got fried during the first test, but I don’t know which components to check, any help appreciated ???
Here’s a snapshot of scope and spectrum taken WITHOUT the 8580 chip
EDIT: oh, don’t look for stereo snapshot, as only the problematic SID module is connected to the oscilloscope
Wow, that’s a nice spectrum of something between white and pink noise!
A question that comes to mind is: how loud is the noise? If there’s a broken connection in the audio-path and you crank up the volume you can always generate noise of this type, but if this noise is really loud (the same loudness of a SID output) then something else is actively producing this noise. A couple of things come to mind:
Check if the problem isn’t coming from a dirty power rail. If something got damaged due to the sparks and smoke you should be able to see this with your scope. An unstable power supply could cause this noise.
Transistor T1 could be damaged due to voltage peaks when the sparks and smoke were going on
swapping the chips has no positive effects, and anyway the noise is present even without the chip (and really loud) so I can exclude that the problem is related to the chip.
I’d exclude also problems related to power supply, in fact with the other SID module the noise I get is much lower, i.e. volume not comparable to SID output.
