OBERHEIM SYNTH

I would start with downloading service documentation:

http://www.google.com/search?q=Oberheim%20OBX-A%20service%20manual&ie=utf-8&oe=utf-8

Then PSU, maybe it needs recapping.

Then cleaning and reseating all connectors, IC's in sockets...

Keys need also cleaning, finding what's wrong with those not working,  
and repair it.

Then calibration as described in the service manual.

Maybe this way you can find where's problem, and change failed  
components.

Good luck!

Daniel Forro

On 7 Dec, 2013, at 8:13 AM, <pyjamagroove@...> <pyjamagroove@... 

 > wrote:

>
>
> Hi everybody!
> I have obtained a OBXA 120 patches model recently. It was in full  
> working condition ( I saw the demonstration by Skype). But after it  
> finally came to me I´ve noticed some problems:
> 1. Two keys are stiffer and are not working
> 2. Entire memory is wiped out - there is only noise with some  
> modulation (battery shows 3V and is not leaking, manual mode works.)
> 3. I can´t write any patch to the memory - instead of writing it  
> goes to the chosen "noise" patch.
>
> There are no apparent loose components or connectors. Everything  
> seems to be in place. Where would you start the diagnostics? Thanks  
> for any help.

Here are factory patches:

http://www.lazyblueoctopus.com/html/oberheim.html

Try to load them.

Daniel Forro

On 7 Dec, 2013, at 8:13 AM, <pyjamagroove@...> <pyjamagroove@... 

 > wrote:

>
>
> Hi everybody!
> I have obtained a OBXA 120 patches model recently. It was in full  
> working condition ( I saw the demonstration by Skype). But after it  
> finally came to me I´ve noticed some problems:
> 1. Two keys are stiffer and are not working
> 2. Entire memory is wiped out - there is only noise with some  
> modulation (battery shows 3V and is not leaking, manual mode works.)
> 3. I can´t write any patch to the memory - instead of writing it  
> goes to the chosen "noise" patch.
>
> There are no apparent loose components or connectors. Everything  
> seems to be in place. Where would you start the diagnostics? Thanks  
> for any help.

Thanks. The PSU seems OK, the cmos drainage too.

I can´t load factory presets - after switching enabling the back switch for external audio the outside signal is mute ( can´t monitor it through audio out). It seems like the memory access is shut. Is there a circuit on some board that I could check for this?

Ok. So here's the story. The middle hood support (big heavy column) was found under the keyboard. It broke loose during transport and could cause some physical damage. I have not found any visible damage yet.

I've managed to load the factory presets with no error finally but after turning the cassette interface back off there were no presets saved. It seems like the memory protection is always on (the switch does nothing)..... Instead of saving a new patch it simply calls it's location.

Can you guys tell where are memory ICs located and how to test them?