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Vintage Synth Repair

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RE: Korg SQ-10 - wavering in pitch...

2013-11-06 by <wmc_mick@...>

I'm in the process of repairing a Crumar Composer and I have found some bad traces on the pcbs, bad ic sockets and dry solder joints. When you say the symptoms are what they are I really suspect bad connections since the Crumar acted the same (unstable cutoff-frequency, resonance etc). I found some bad connections by pressing the pcbs at different points but some signals I had to trace with an oscilloscope to find.

Obvoiusly the problem is due to something that all steps 2 > 12 have in common, power lines come to my mind, would it be possible that one of the power lines goes bad due to break in trace or something else after the circuitry for step one? I have had that kind of problem with polyphonic after touch on a master keyboard where seven keys did not send after touch due to a cut in the common power line for eight keys.

- Mick

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