[sdiy] Frozen DX7IID

[greg at gzifcak.net]

Thanks for the insight; I hope this isn't the case because I haven't been
able to find replacements with the exact suffix. If that is what's causing
it I'll just take them back out and live with a functioning synth with no
patch memory. I usually program it from scratch anyway, but it would be
nice to be able to save.

> 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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