[sdiy] Help: Oberheim OB-Xa won't bend up

[tprivitera at nc.rr.com]

Hi Everyone,

My OB-Xa just out of the blue will not bend up at all with the pitch bend paddle (neither Osc).  Bends down just fine and returns to center (wide and narrow) and the low and high octave switches work just fine, as do all the rest of the modulation board functions.  All functions of the keyboard itself and the control panel work just fine.

The pot itself seems to test fine with my meter (I can see resistance moving up and down while moving the paddle) and as I said, it just stopped working today, so it wasn’t like the pot was wearing out.  This is what I’ve done so far after looking at the schematics:

-	Replaced U13 and U14 on the modulation board (4053’s replaced with new)
-	Checked all connectors on modulation board and lower control board
-	Tried to adjust the ‘bend up’ adjustment trimmer on the mod board – no changes at any range of adjustment
-	Replaced U14 on the lower control board (4053 replaced with new)
-	Replaced U46 and U50 on lower control board (4051’s replaced with new) – had the hood up to replace these chips for a different reason, not sure they are associated with this issue, but I swapped several new ones in there to confirm
-	Power supply has been totally rebuilt and calibrated

I’m kinda at a loss.  Any ideas?  Anyone seen this before?

Thanks,
Tim