[sdiy] Trying to fix an sh-101.

[Julian]

Now that the Wasp I was trying to fix the other day is sorted, thanks to help from Laurie and Harry (it was a dead 4016) im now on to the dead SH-101 that's been knocking around here for ages.

The synth is silent from its own keyboard.  If I trigger it from an external gate, via the GATE input then the envelope opens and all is well.  Whilst the envelope is open, the keyboard will control pitch, just like you'd expect.

The GATE output jack is at a constant 1.1v.


The CPU output P27, connected to R49 (I cant find a datasheet for the CPU - toshiba TMP80C49P-6), falls from about 4.4v to 0 when a key is pressed.  My knowledge is now not good enough to know why I don't see any voltage change on any of the legs of YR9 on keypress.  

Im having trouble working out the rest of the gate or trigger on the schematic now, but that first bit isn't right anyhow.

The P27 CPU output seems, from the schematic, to only control the GATE out jack, but I cant think that the symptom of the signal not getting to the envelope isn't down to the same cause, so im confused.

Anything spring to anyone's mind?

Thankyou, Julian

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