OBERHEIM SYNTH

Still having a problem with the D3 line on the data buss.Pulled eveything from the processor pcb- nothing shorted to ground.The D3 line only swings to abpout 2.5 volts.I even got a NOS processor. Only thing left is the PROMS or the resisitor arrays.Ever seen PROMS go bad?

As I have said before, any blue tant capacitors should be replaced.  Even if they are not "shorted", they many not have the required very high resistance to ground.  It is possible one or more caps "partially" failed, and now you have a resistor(s), rather than a capacitor, in the circuit.  This could be the cause of the low voltage.

I had just this problem with a capacitor related to my DC memory storage.  That is, the capacitor partially failed, it became a few 100k resistor (rather than several Megs) and I was draining my back-up battery it just a few weeks, as opposed to a few years. 


--- In oberheim@yahoogroups.com, jim finch <jahg88@...> wrote:

>
> Still having a problem with the D3 line on the data buss.Pulled eveything from the processor pcb- nothing shorted to ground.The D3 line only swings to abpout 2.5 volts.I even got a NOS processor. Only thing left is the PROMS or the resisitor arrays.Ever seen PROMS go bad?
>

One other thought.  My board has/had a strange habit of sending of sending a biased voltage to VCO2 (about .25V as I recall).  I traced everything back to the A/D converter and all was well (0V).  However, when the single got out of the D/A converter the .25V was back. 

Drove me crazy.  

The only way I could fix it was to cycle through all of the program patches and for some reason I could always find at least one patch where the bias was not there.  I then had to copy this patch, or some variation of it, to all other patches, and then things worked fine (and stayed good until the memory battery died).

This is some strange memory/software glitch.  The best I could tell all the hardware worked perfectly. 

Anyway, this might give you some ideas on how to fix your problem.

I always figured that if my code went bad, I would try to track down the Encore Midi upgrade - it seems to replace all of the code.  Problem is it is designed for boards with the dip switches rather than the big switches we have.  That should be a relatively easy hardware swap if need be.

Good luck, I hope you get it figure out.  

I am still searching for a source of voice board connectors (PCB to posts) so I can replace my old worn ones.  I have e-mails in to Digikey and Mouser asking if they can identify the parts and if they sell replacements.  If anyone know a source, please let me know.

Thank you. 

--- In oberheim@yahoogroups.com, jim finch <jahg88@...> wrote:

>
> Still having a problem with the D3 line on the data buss.Pulled eveything from the processor pcb- nothing shorted to ground.The D3 line only swings to abpout 2.5 volts.I even got a NOS processor. Only thing left is the PROMS or the resisitor arrays.Ever seen PROMS go bad?
>