OB-Xa EPROM image (Rev C) is available here if interested:
http://www.lazyblueoctopus.com/html/oberheim.html

--- In oberheim@yahoogroups.com , Martin Ator <cyllall@...> wrote:
>
> If you have an Eprom reader then there would be no harm in trying to read them off. You can then try and verify the buffer with the Eprom, or look at the read file in a hex viewer. If you have a UV Eprom eraser and can erase the Eprom, then reprogram it with the file you read off and then verify it and all checks out, then it probably isn't the Eprom.
>
> Your saying that all the data lines are OK. Check that any buttons aren't shorted especially memory protect ones etc and also check Digital to analogue/analogue to digital sections for correct outputs/flaky zener diodes etc.
> I have a JX-3P that's giving me similar problems.
> I'm sure you've checked the power supply but what about the -5volts.That's an easy one to overlook.
>
>
>
> ________________________________
> From: Doug <dmeek@...>
> To: oberheim@yahoogroups.com
> Sent: Thursday, 29 November 2012, 20:08
> Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed
>
>
> Â  
> Hi Martin, thanks for your suggestions.
>
> The reason I suspect the EPROM is because of experience with a Textronix
> 468 digital scope. It was suggested that I replace the EPROMs. I was
> sceptical, but did it anyway and it worked!
> Nor sure if reading and reprogramming the chips would work. If the OB-Xa
> can't read them would the EPROM reader/programmer be any different
> Like you say it would show a bad eprom, then I would need new bin files.
> I checked all address and data lines with the scope. They all look ok.
> I replaced the UPD780 CPU and 6116 CMOS ram - no change.
> I replace the two 2114 RAM chips and there was a difference: there was
> no flickering, some random LEDs were on, some buttons had an effect,
> some not. Still no sound.
>
> I've posted two photos of the board to the Photos section
>
> Doug
>
> Posted by: "Martin Ator" cyllall@... cyllall
> Date: Wed Nov 28, 2012 7:31 am ((PST))
>
> It's probably something to do with the Midi mod so have a look around
> for anything suspicious, wires/broken tracks etc.
>
> It's very rare that you get problems with an Eprom, they are very tough.
> If you can read them with a programmer then UV erase them, then
> re-program them any problems will show up. Having said all this however,
> static is an enemy of us all. It depends how safe you are in this
> respect as to what possibilities may arise during troubleshooting.
>
> It is much more likely that another IC is damaged/has been damaged by
> static or other reason/age etc, the main cause possibly being problems
> created during the installation of the Midi mod. EEproms (Eproms that
> aren't ceramic with a little erase window) can develop problems over
> time as they are erased/programmed with much lower voltages.I would not
> expect an OB to have these types installed.
>
> I don't have any OB series synths. If there is a back-up memory system
> involved, then a big candidate for suspicion are the memory chips
> involved as any hint of static while checking the battery or replacing
> it is liable to damage the memory chips. I would look here first for
> problems if it was me.
>