Realistic Concertmate Moog MG-1

Restoring this mini synth was a long process as the electronics in it is highly interactive and tends to mask the root cause. A previous repairer had replaced all of the sliders and switches, along with cleaning all of the goo from the control panel where the original foam had deteriorated. The switches and sliders still needed vast amounts of switch cleaner to get them crackle free. Cleaned the keyboard contacts also. The symptoms were then a thin sound, crackles, and the contour was misbehaving. A mod had been wrongly applied which injected earlier audio onto the volume control Moog MG-1 Keyboard and second circuit board rather than aux-in; removed this mod. Transistor Q28 which is associated with the audio out (LM3080) was causing the crackling and very low sound from cold. The contour issue was the LM741 (U8) which is a summing amp. Thankfully Anchor Electronics had some of these obsolete LM741’s.