Thanks for the info! I finally did get it semi-working after changing out some 7442's on the upper board and control board and installing the Encore midi kit. A lot of the chips directly underneath the upper board can cause the front panel to lock up just as easily as those on the upper board. Especially the ones feeding the ribbon cable that leads to the pot boards.

Still doesn't fully work though. All of the buttons are working but none of the CPU controlled pots are working. And though the OSC 1 pulse wave button does light up when pressed, OSC 1 goes silent instead of turning to pulse for all voices. OSC 2 is fine.

Nice to get some control over this thing finally...it even auto-tunes correctly. And 7 out of my 8 voices are functional, with one just having a bad voltage regulator on the -15v rail, so hopefully once I get that part, all 8 voices will be up and running!

Can anyone tell me how to remove the knobs on these pots They do not seem to slide off easily and I don't see anything holding them in place. And any help trouble shooting the non-working pots would be appreciated. It looks like the 3 4051s on the pot boards are important for the pots, but I'm not sure what other component would take down all of the pots at once..

Thanks for any help anyone can offer...

--- In oberheim@yahoogroups.com , "doug1052365" <dmeek@...> wrote:
>
> I finally had to give up and return it to my customer. It didn't make
> sense (or dollars) to continue. If I owned it I would still be poking
> away at it I guess. One thing I didn't mention before is that the
> bridge rectifier on the 5V supply was burnt, so maybe some negative
> voltage could have got on the +5V supply line. I changed every chip on the upper board. The only ones that made any difference were the
> RAMs. No improvement, just different.
>
> Good Luck
>
> Doug
>
> ps check every button with the ohmeter to make sure they are all
> working. Corrosion can get in there and cause problems.
>
>
>
> --- In oberheim@yahoogroups.com , "leavesstillgreen" <errorspending@> wrote:
> >
> > Did you ever figure this out I'm bringing an OBX back from the dead...like really dead...as in corroded, and probably a previous home to rats. Geeze it's a mess.
> >
> > Mine actually started making sound sometimes, after fixing the socket that the z80 was in. But the front panel is still non-responsive except for a few things.
> >
> > I completely rebuilt the power supply, so that is rock solid. The edit,manual and auto buttons make it do weird things...volume and master tune work...mod wheel works, and the octave switch....some of the randomized patches that come up when booted have working portamento/noise/sample+hold/cross-mod/unison and it cycles through the 4 voices just fine, though they are certainly out of tune. Some success....
> >
> > I'm guessing some of the Eproms must be working in order for me to be able to play the random patches....but I don't really know enough.
> >
> > I'm not sure where to go from here though.... I don't own an oscilloscope, only a DMM...and no eprom programmer...
> >
> > Any advice welcome!
> >
> > Thanks!
> >
> > For now I will probably recap more of it and change out more cmos chips. I guess I should try replacing the memory chips.
> >
> >
> >
> >
> > --- In oberheim@yahoogroups.com , "wesleyknick" <wesknick@> wrote:
> > >
> > > Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice...
> > >
> > > --- In oberheim@yahoogroups.com , Martin Ator <cyllall@> wrote:
> > > >
> > > > What is the function of the LM311 in the circuit
> > > > (If I had a teleporter I could pop round with my Boardmaster 4000)
> > > >
> > > >
> > > >
> > > >
> > > > ________________________________
> > > > From: Doug <dmeek@>
> > > > To: oberheim@yahoogroups.com
> > > > Sent: Tuesday, 4 December 2012, 19:11
> > > > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed
> > > >
> > > >
> > > > Â  
> > > > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80
> > > > (divided by 2 by IC A116). CPU reset circuit is OK
> > > > A Christmas tree ornament sounds like a good idea.
> > > >
> > > > Doug
> > > >
> > > > 1b. Re: OB-Xa Diagnostic EPROM needed
> > > > Posted by: "wesleyknick" wesknick@ wesleyknick
> > > > Date: Mon Dec 3, 2012 4:43 pm ((PST))
> > > >
> > > > 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.
> > > >
> > >
> >
>