The Moog Prodigy is the slightly bigger brother of the Moog Rogue. Features-wise, it is the next “step up,” with the important addition of two ADSR generators (in which D must equal R, however) but some of the same limitations. This one seemingly just needed calibrating but a couple of issues came up that needed to be taken care of before it could be finished. The first issue was a failed transistor in the synth’s “heater” circuit. The transistor is used to turn the circuit on or off, allowing the synth to regulate the temperature of the oscillators’ exponential converters. This is key to allowing the synth to remain in tune while the synth’s temperature fluctuates. The other problem we noticed was the pitch of oscillator 2 was unreliable, quickly wavering in and out of pitch. The problem would appear after being on for about thirty seconds, which suggested the culprit was a cold solder joint. I reflowed the joints in the area and the problem went away.
Work done: replaced failed 2N3904 transistor in oscillator 1’s heater circuit, reflowed oscillator 2’s solder joints, replaced power supply capacitors, calibrated to factory specs.
Note from Alison: this is the 5th or 6th Moog we’ve worked on from the late 70s and 80s that had a problem caused by cold solder joints. I recommend reflowing all solder on pin connectors and wire connections on all Moogs of this age, and the solder in any other area where any strange behavior is seen.