Doug, I've been following the email traffic on this issue rather sporadically however now that you've described in detail again I can certainly say I have a funny feeling the crystal on the upper control board is bad (next to the memory protect switch). If the quartz crystal oscillator next to the processor IC chip is bad, the processor will process nothing as it sets the processor speed which if I recall correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise if it doesn't set the correct processor speed either. I own two OB-Xa's at the moment and one of the two exhibited exactly the same symptoms you are describing - some of the LEDs will illuminate when the unit is powered on but will not respond to the buttons, and the modulation panel will still seem to function normally. Power on, off and back on again will sometimes change the configuration of LEDs that light up but the unit will still seem frozen and not respond to the buttons. I had the very almost identical problem a didn't realize the crystal was bad unit I removed the upper and lower control boards and heard something rattling next to the memory protect switch. The quartz crystal inside the housing had physically broken off an was rattling around. Sounded like a miniature cow bell. Swapped it out and the OB-Xa's worked great ever since. Took me a while to figure the crystal was the problem and I got so frustrated I wanted to just give it up and hang it from my Christmas tree as it was about the only thing I could think of to do with the pretty LEDs that would light up on the top it and do nothing else. Try changing the crystal and see if that does anything... I recently repaired a Matrix 6 with this similar issue.

--- In oberheim@yahoogroups.com , Doug <dmeek@...> wrote:
>
> Since I don't own this keyboard I may have to call it a day soon.
> I tried removing the MIDI board and burning the 3 EPROMs from
> http://www.lazyblueoctopus.com/html/oberheim.html. Still no go.
> Some LEDs stay lit, some are flickering, most are off and the
> buttons do nothing. Curiously the LEDs and buttons on the Bender
> panel have always worked. However it appears the problem is not
> the EPROMs. So I'm back to my original request: Diagnostic EPROM.
> I'll keep the keyboard for another week, then return to customer.
> Thank you to everyone for the suggestions. The one about a stuck
> button was a good one, I've seen it before. But not this time.
>
> Doug
>
>
>
>
>
> 1a. Re: OB-Xa Diagnostic EPROM needed
> Posted by: "synthparts" synthparts@... synthparts
> Date: Mon Dec 3, 2012 1:58 am ((PST))
>
> Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the
> OB-Xa with JL Cooper MIDI and Rev C processor board if you need it.
>
> Doug
> synthparts.com
>