[sdiy] Oberheim OBXA issues

al spitzley kogz23 at yahoo.com
Sun May 1 01:25:19 CEST 2022

Hello all,So I am working on a DOA OBxa. I've got it up and running after power supply rebuild and a lot of troubleshooting.
Now I'm stumped with a couple of issues that could be related to each other.

Firstly when I enable the cassette mode it doesn't seem to go into the mode. The Cassette LED does light, but the other LEDS do not go out. The Play button or seemingly any other button are non responsive.

Secondly when I write a patch to load the patch I have to hold the relevant Program button. As soon as I release the button the patch disappears.
Scoping the power rails shows a significant amount of noise. If I disable the clock the noise goes. I've tried replacing numerous ICs around the CPU, including rebuilding the clock but still there is a bunch of noise. I'm hoping this noise is causing the issues I've mentioned but am struggling to work out what is causing it. Or maybe that is not the problem?

Any ideas greatly appreciated. 
Thank you!
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