Joystick Problems
2013-05-27 by John Henson
Hi List, I recently repaired a Mark 1 Poly 800 with an unusual problem. The joystick would pitch bend up, but bending down just introduced filter mod and no pitch bend. Osc mod and filter mod worked fine. Occasionally the synth would burst into spontaneous modulation. Tuning was also poor. Diagnosis was not easy due to the poor quality and confusion of the schematics. I first replaced IC10 as it's output voltages were strange when the joystick was waggled, but that wasn#t it. My instinct led me to IC6 which is a multiplexer ( a 14053 CMOS chip ) which when cut out and replaced solved all problems. Don't bother trying to desolder the chip, you risk damaging the board and the chip is cheap (less than a dollar almost anywhere in the world) I remember someone on the list had joystick problems a few weeks ago, so maybe this could be of help. John.