Crumar’s T1 is a surprisingly nice 70’s drawbar organ that used the latest octave divider chips that were present in a lot of keyboards of that era. An additional feature that makes it more useful than your average organ is the addition of a very rich, fuzzy bass synth voice that can be added to the lower octaves of the keyboard. The synth voice has a basic resonant filter and a decay envelope that you have some control over. The organ voices sort of drop out in the bass section, so it really helps add a thick low end that would otherwise be lost. It also has a really nice LFO that can be applied as both a tremolo and a vibrato and the speed is controlled with a rotary pot.
This organ was displaying some odd, intermittent behavior. If left on for a while, a quiet, variegating noise would emerge in the output. It would also sometimes appear to freeze up and only the bass synth would work, the LFO would stop oscillating and there would be no organ in the output. The noise was eventually traced to trim pots, of which there are many in this organ. To track down a bad trim pot, I just gently press on them and wiggle them a little bit. If the trim pot is bad, the problem is exacerbated by the movement and it’s obvious if it needs to be replaced or not. Not the most scientific approach but it works. The other problem wound up being caused either by a dirty pin connector or a cold solder joint that was blocking voltage from getting into the board that holds the master oscillator and LFO circuits. I reflowed any solder joints that were between the pin connector and the ICs on that board and cleaned the pin connector and the problem never emerged again. I then proceeded to clean every pin connector in the entire organ to prevent it from happening to other boards.
While I was working on this organ, one of the octave dividers died on me. One really nice thing about this instrument is almost every single IC is socketed, which made troubleshooting and replacing the bad chip much easier.
Work Done: replaced dirty trimpots causing intermittent noise, cleaned all pin connectors, reflowed solder joints on master oscillator board, rebuilt the power supply, replaced bad octave divider chip.