EmptySet wrote:Wait! Before you go replacing parts, I'm wondering why no one has suggested first plugging in MIDI and sending some notes to the synth? Wouldn't that help troubleshoot if there is something really wrong with the synthesis part of the 3P?
Well, it is possible that some of the troubles may be key-assigner based, but having voices respond differently according to wether or not a sawtooth or square wave patch was being used indicates a bit more trouble under the hood...
Also, the two vids he posted showed differing keyboard behavior. One vid showed every third or fourth note dropping regardless of where he was on the keyboard, and the other vid showed the synth dropping every other note. That's why I skipped the "use a midi keyboard test", as the first video clearly showed individual voice issues.
Of course, what Vincent has posted so far indicates enough differing issues that plugging in a midi keyboard wouldn't be a bad thing to try, because if it responds the same as with the internal keyboard, we know we're on the correct path. If it responds with totally different symptoms than before, well, then there's more to look at.
Right now though, there are basically 2 and a half voices out.
@Vincent: On voice 6, the waveshapers share the same chip, IC604. However, there could be many other things on that voice making it misbehave other than the opamps, such as TR601, which basically is what allows that 4558 to act as a VCA, and transistors TR605 thru TR608 as well as IC605. It could also be as simple as a cap gone bad, or even a broken/bad solder joint.
IC26, a 4051, handles sending the CV for all 6 VCAs, so the issue could boil down to that one single chip, or it could be IC9, which is the buffer feeding the VCA on voice 6. IC11 and IC12 feed the VCAs to voices 3 and 4. To do a quick test on these, set the VCA to "Gate" instead of ADSR, and one at a time, check for a voltage change from zero to +5V or so at the following places: IC11, pin 1 (voice 1 VCA). You said this voice was working, so keep the DMM on that pin, repeatedly press a key until you get a reading, take note of the reading, and compare it to the following places: IC12, pin 7 (voice 3 VCA), IC11, pin 7 (voice 4 VCA), IC9, pin 1 (voice 6 VCA), again, press a key until you get a reading. However, once you get past six to twelve tries with no reading, you can assume that you won't get one at all. If you get readings on all pins above, All those chips plus IC26 are good, and you go back to checking stuff on each voice.
If you get no reading on a certain pin, check the input for signal from the 4051 chip. If you're getting no output on pin 7 of a chip listed above, check for input on pin 5 of the same chip as you cycle through the keys. If you're looking for output on pin 1, then pin 3 is your input. Do this test a couple times to make sure. However, if you're getting no input on even just one of those pins, you'll need to swap IC26. IF you're getting input everywhere, but no output, well, you've found your dead opamp.
If none of this makes sense, let me know!
Once again, good luck!