@seriescircuitsaudio

Another poly-800, this time with cool reverse keys! 2 dead ICs causing it to not boot and show no signs of life, IC 33 and IC 23. Classic poly-800 problem, trouble is it's always different ICs! The poly-800 design makes it such that there are lots of things that can go wrong that will throw off the entire system and make it appear dead. IC 23 is the address latch so the outcome of that failing is self explanarory. The interesting one was IC 33 which is the encoder IC for the front panel switches/buttons, it was holding up the whole address line by being unresponsive. Here's how I figured out the problem: - First off scoped the address latch chip as this is always causing problems, as predicted it has outputs that weren't moving - Removed it (IC 23) and tested it, failed - Replaced and socketed a new chip into IC 23 - Try to turn on poly-800, still won't boot! Seems to be in a similar state as before - Scoped around the logic chips until I located the output of an OR gate which wasn't changing even though I could see activity on the inputs (pin 3 IC 16) - Removed the OR gate and tested it, tested ok so I put it back in - Removed IC 33, the OR gate output is connected to output enable 2 pin of the IC, so the entire thing would be thrown off without the right signal there. - Tested IC 33 and it failed! Only time it's relieving to fail a test is repairing vintage synths - Replaced and lo and behold she works again Give it to me if yours is dead! 100% success rate on lots of poly-800s so far 😃 #synth #synthesizer #vintagesynth #vintagesynthrepair #mods #korg #poly800 #polyphonic #roland #yamaha #oberheim #moog #80s #80sdesign #vintage #seriescircuits #analog #digital #sequentialcircuits #808 #909 #303