Well, I’ve just about finished the project when I’ve hit a wall. This morning the midisid was responding to midi notes and CC … very nice.
But I noticed there was a problem with the long bridge on the bottom of the sid board. When I pushed it down, the sid would stop making noise. So I replaced the wire with a shorter piece and now I’ve lost all sound! So I’ve begun looking for the problem, with no success.
My voltage on IC 2 & 3 on pins 16 is 4.8V
The voltage on IC 1 pin 25 is 4.8V
But the voltage on IC 1 pin 28 is only 9.7V even though when I check the voltage across the C10 cap is 11.0 V.
I’m using an old C64 psu.
Is that a problem? It’s strange that it was working… Any help is very much appreciated!!!
yes, the voltage at pin 28 is the problem, once it’s below ca. 10V, you won’t hear the sound anymore. Also the voltage at C10 is too low, it should be >= 14V
Maybe the C64 PSU you are using doesn’t deliver enough voltage for the simple PSU circuit, you should consider the use of the optimized PSU - all parts can be canibalized from a C64
the 10mV at the CS# pin are ok. If all signals can be toggled from the core, then it’s either a very general problem (e.g. notes played on the wrong MIDI channel), or there is a problem with the clock (oscillator - one guy just had this some days ago, he mounted this part in the wrong direction) or the audio stage of the SID module (around transistor T1)
In order to exclude those “general problems”, I’ve written a testtone applications which is available at the MIOS download page. Once you’ve loaded this app into the core, the SID should output a 1kHz tone. I hope that this helps you with debugging.
At one point, using my volt meter (I had all chips in the sockets, the unit was plugged in) I had a small electrical arc between my volt meter and one of the legs of the voltage regulator. Is it possible that I could have fried the sid? I’m going to try another sid and see if that fixes it.
At one point, using my volt meter (I had all chips in the sockets, the unit was plugged in) I had a small electrical arc between my volt meter and one of the legs of the voltage regulator.
It could be, that this was caused by a temporal short circuit caused by the probes. The propability that this fried your chips is low, but it cannot be excluded.
I just had an idea for a simple check of the transistor amp circuit: instead of using the SID, you could attach another audio signal (e.g. from a radio or a walkman) to pin 27 of the empty SID socket. You also need to connect the ground to pin 14 - now you should hear some sound at the audio out
OK. The problem is in the audio out. When audio was applied, there was some output, but it was very quiet, “poppy” , low frequency and heavily distorted. Kind of “farty”. When I run midi into it. I can hear the sid reacting and making little audible pops.
OK.  The problem is in the audio out. When audio was applied, there was some output, but it was very quiet, “poppy” , low frequency and heavily distorted. Kind of “farty”. When I run midi into it. I can hear the sid reacting and making little audible pops. Â
Could this be the transistor?
did you check your Ground-Connection @ audio-output? Sometimes, this is a real common problem with crappy and noizy sound?
