Been sick and stuck at home for the past week, so I finally got a chance to get my Farfisa working perfectly. Some of the issues included notes that could not get in tune +/-8 semitones, notes without vibrato, notes with missing frequencies, and notes with a strange beating noise.
Almost all of the issues mentioned above can be fixed with a bunch of 1uF caps and 2N3096 transistors. Each sound card has convenient tabs for attaching a scope probe to view the waveform. Each tab is labeled on the copper layer of the PCB. Generally, if I saw an issue with a waveform, I first swapped out the corresponding 1uF cap. If there was still an issue, I'd trace the corrupt wave back to the transistors. If the corruption traced all the way back, I'd replace the transistors. I noticed a few times that the wire connected to the vibrato tab broke off on a few cards. Check for this first if you are missing vibrato on a few notes, it is an easy fix.
I also had a friend crawl out of the keyboard while I was repairing it. Almost had a heart attack. It was the last thing I was expecting while repairing a keyboard.
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