I know that it's not power supply related.I have replaced some of the tantalum caps that fried on one of the voice cards.Yes, I know what the voice cards are :).I have a four voice model.It is the D3 data line thats causing the problem.There's only about seven or eight chips that use the data buss.From experience,usually buss latchs,74244,245 or 373 tend to fail first.There is a tantalum cap used in the reset for the proceesor but reset timing looks good via O-scope.
Yeah ,I know they are worth alot-less than 1000 were made.I do have extensive digital troubleshooing experience,just not with stuff quite this old.I have to dust off what I learned 20 yrs ago to fix this one.
Object is to get it up and running 100%,then sell to the highest bidder.I have an OB-8,along with 14 other keyboards,mostly old analog stuff.Wife says I have to sell some of it.Little does she know I'm going to spend it all on Ebay!