Oberheim Xpander

The service to this instrument included replacing the capacitors in the power supply, fixing a problem with a voice, and replacing the rotary encoders.  The voice problem was cause by a failed 4501 Multiplexer in the  D/A section.  The encoders were replaced with Mouser part 652-PEC092325KN0015, and the shafts were fitted with a rubber “O” ring and washers to position them properly.  The 0.1uF debouncing capacitors were replaced, and after much experimentation, another 0.1uf capacitor was placed across the encoder terminals for smooth and reliable debounced operation.