[sdiy] Frozen DX7IID

[MTG]

If it's anything like the vanilla DX7 they require almost exact 
replacements. There is something funky going on with the memory 
addressing or the assertion or de-assertion of the control lines but 
I've never really had the time to examine it. On the regular DX7 I had a 
bad SRAM and tried quite a few standard types that *should* work but 
they don't. I had to resort to buying a new one of pretty much the exact 
type (manufacturer too).

Maybe someone knows what Yamaha is doing that makes it so picky. There 
are so many expansion boards out there (E! et al) that someone obviously 
knows.

GB


On 8/21/2014 1:37 PM, greg at gzifcak.net wrote:
> Hello,
>
> I just replaced the RAM in my DX7II. I swapped the existing Toshiba
> TC5564PL-15 chips for TC5564APL-15 since this is all I could find
> available. I searched for info on the meaning of the suffix but couldn't
> find anything.
>
> Anyway, I did not try powering it on before I did the repair, but it
> worked fine (aside from the RAM) when I last used it about a month ago or
> so.
>
> When I powered it on after replacing the RAM chips, all lights came on and
> the screen is blank except for the top row, which is showing solid bars.
> It is making no sound and no panel controls have any effect.
>
> I probed around with my scope and the sub-CPU and main CPU are both
> receiving clock and show approximately 5v on the power pins.
>
> Any ideas what else to check or should I hunt for replacement CPUs?
>
> Thanks in advance,
> Greg
>
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