[sdiy] FW: DX7 Memory Problem

[gregory zifcak]

8 x 8k rather, 64k.

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> From: zifcak at hotmail.com
> To: sounddoctorin at imt.net; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] DX7 Memory Problem
> Date: Sat, 18 Aug 2012 23:39:04 -0700
>
>
> Cool, thanks for the info. Yeah I have memory protect off. I found the self-test procedure and it fails at the RAM check. I will check the chip enable lines as you said; I'm guessing one or both of the RAM chips died. The chips are 8k, part number TC5564PL-15. That would be great if you have some spares.
> Greg
>
> ----------------------------------------
>> Date: Sat, 18 Aug 2012 22:20:17 -0600
>> From: sounddoctorin at imt.net
>> To: zifcak at hotmail.com
>> Subject: Re: [sdiy] DX7 Memory Problem
>>
>> On 8/18/2012 3:45 PM, gregory zifcak wrote:
>>> Hi all,
>>> I have a DX7 II that all of a sudden stopped saving patches. I was in the middle of sequencing it when all the patches disappeared and I can no longer save anything, or dump via sysex. I can still program in the edit buffer, and this gets retained on power down. Battery voltage is healthy.
>>> I replaced the battery when I first got it about a year ago and it was working perfectly until this problem appeared.
>>>
>>> At one point even the patch I was working on started to degrade into seemingly random settings. I don't really have experience with digital electronics, but I'm guessing this may have something to do with the RAM chips? I don't know why this would cause the edit buffer to degrade though.
>>>
>>>
>>> Thanks in advance for any tips,
>>> Greg
>>>
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>>> Synth-diy at dropmix.xs4all.nl
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>>>
>>> You
>>>
>> You do realize that you have to turn on the sysex 'flag' and memory
>> protect right? If so, then you need to scope the lines for chip enable,
>> Write enable to see if they are going down and up as they should during
>> the write operation. Possibly the line that controls that is bad
>> somehow... I'd have to look at the schemos to figure out if there's
>> something likely to fail in between there. I personally haven't seen
>> this issue on dx's though. BUT if you need it I probably have a scrap
>> chip maybe...trying to recall..I think we had a scrap dx7 board then
>> again I might have sold it. Trying to recall. Let me know the number.
>> That part might be common to DX27 etc. which I do have a scrap unit of
>>
>> --
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>