MATRIXSYNTH: Oberheim OB-X Analog Synthesizer SN 793903

Thursday, January 18, 2018

Oberheim OB-X Analog Synthesizer SN 793903

via this auction

"This OB-X is not functional. The tag says 4 voice, but it was at one point upgraded to six (see pics). The power supply does work, and when disconnected from the rest of the keyboard all of the voltage rails are present and regulating. Replacing the tantalum caps that sit on the voltage rails on 4 of the voice cards (and the supply) permitted those voice cards to power up, but it's obvious that something(s) on the main board are pulling the supply down. The main board has many RCA CMOS chips installed, which are notorious for failing, but cheap to replace. There are numerous failure prone tantalum caps on the main board as well. Many of the "tropical fish" style caps are cracked and would also need to be replaced. The keys could use new bushings to eliminate the clack when you release a key. This list of issues is merely what I've found for an hour or two of diagnosis, there are likely more issues beyond what is listed here."

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