keyboard ageing problems

Lincoln Fong linc at christeld.freeserve.co.uk
Tue Jul 18 00:11:34 CEST 2000


Maybe someone can help with this: I'm having a bit of mis-triggering trouble with an Oberheim 4 voice I'm repairing. A high pulse scans the diodes/keys then feeds a 100K resistor and debouncer on a different board. If you look at the signal arriving down the (shortish) cable it's riddled with significant sized echoes of the key presses which may be the trouble. I'm about to clean up the contacts but can someone tell me what causes these echoes that confuse the polyphonizer? Is it charge in the cable or on the key common rail?? It always seems to be the same note intervals (ie 8 notes apart) that give the most trouble which would suggest the logic but that doesn't explain the echoes. Any quick fixes? Tried changing the cable length to no avail. 
Any help gratefully received.

Linc

Linc at christeld.freeserve.co.uk
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