[sdiy] Prophet 10 on fritz again.

[Steve Galle]

This instrument continues to exhibit lots of character...

This time various parameters of patches (it's hard to say which, maybe all) are drifting as it warms up, until patches no longer resemble anything similar to what they're supposed to sound like. It's affecting all voices of both voice cards, so it seems like it's got to be something on the CPU or power supply I'd think. The polymod circuitry is independent for the upper and lower voice cards so for now I'm ruling that out. The cpu also remains stable so I'm thinking it's probably not an issue with the +5V. So I think maybe I'm down to the +/-15V power supply rails, and components related to the DAC system. I have a spare DAC71, so I will swap that out tonight and see if that's it. I'll also test the power supply cool and warm. If the supply is clean and the problem persists with the spare DAC then I'm not really sure. There's the lf356 on the output of the DAC; it'd be easy enough to swap in a replacement for that. Also the recent thread regarding capacitors makes me think, maybe the next step is to recap the cpu board. Tedious task to contemplate, but one that I suppose should probably be done regardless...

Any thoughts appreciated; going to test the PSU and swap the DAC tonight, fingers crossed. 

Steve