Vintage Synth Repair

> Pin 36 is always low. One data sheet says this is MRDY, the other says 
> it is AVMA.  MRDY makes no sense as the processor should be in a 
> constant wait state.  What is AVMA?  And, why the difference between 
> these datasheets?

I don't remember for sure but AVMA might be Address Valid.  Which
means that the address lines have finished wiggling and are valid for the
upcoming access.  I don't recall this quirk being present on the 6809 but
I do recall it for the 6502 (VMA).  It was a signal that just needed to
be included in the address decoding.  Annoying.  Do you have a 6809
or 6809E flavour of CPU?

You might just have a bad EPROM or SRAM, though anything that 
hangs the data bus would toast you.

I have a ROM image if you can find a way to burn a new EPROM.

GB