C64 sound problems

[Brent Hilpert]

David Betz wrote:
> I finally got around to checking the 12v supply in my C64 and it seems
> to be working. I also verified that 12v is getting to the VDD pin on
> the SID chip so lack of 12v is not my problem. One thing I noticed
> that I thought rather strange was that the VCC pin on the SID reads
> 5.27v but the output of the 5v regulator is correct. Is there a reason
> why the VCC at the SID would be higher? Could this be causing a problem?

It would seem weird, wouldn't it - however, there are three 5V sources in the C64.
When you say 5V regulator do you mean the 7805 (VR2)? - that is not the supply
for the SID (pin 25), so one can expect a discrepancy.

(I know very little about C64's, just happen to have the SAM's photofact
schematic here.)