Vintage Synth Repair

I'm got much more Intel than Motorola experience.  Here's what I found 
so far.

With the eprom removed, the G (and E) pins cycle more like what I 
would expect with a lost processor.  With the eprom installed, they 
are perfect replica's of the clock.

BS and BA are low - normal mode.
Reset is high - check.

Q and E look good - 90 degree phase shift between them.

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?

Now, to go find the system ram ...

Dave


--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> > I'm having trouble finding a datasheet for a 68B09 processor.  
Does 
> > anyone know where one is posted?
> 
> Just look for 6809 or MC6809 or M6809.  It's a standard Motorola
> 8-bit microprocessor from the 1979 onward.  The B is just a slightly 
faster
> crystal.  If there is an E on the end, then it has a different clock 
drive
> circuit.  There's going to be RAM chip too in order for the stack to
> work, so if the RAM is toast, the program is too.
>  
> > The G- (pin 20) of the 2732 seems to follow the system clock 
(1MHz) 
> > which is screwy.  Anyone have a ecopy of the logic portion of this 
> > part of the schematic?  I'm starting to think the processor may be 
> > bad.  I don't want to invest in a full set of schematics since 
this 
> > whole unit may be junk.  I'd like to at least see if the processor 
is 
> > trying to read data from the eprom.
> 
> Yeah, sounds like it's just cycling the data and/or address lines.  
The
> 2732 would be mapped to the top of the 64k so there should be
> some decoding like a 74138 or discrete logic.  It may include the
> R/W* line.  Also check the RESET signal.  Does the wave at G*
> change when the ROM is removed?
> 
> GB
>