Re: strange 2001N fault

On Tue, Feb 20, 2018 at 5:34 PM, Gerrit Heitsch
<gerrit@laosinh.s.bawue.de> wrote:
> On 02/20/2018 11:53 AM, Francesco Messineo wrote:
>>
>> Hi all,
>> in case someone doesn't read vcfed forums, my 3032 developed a strange
>> fault:
>>
>> http://www.vcfed.org/forum/showthread.php?62202-3032-(2001N)-strange-fault
>>
>> The thread link is just to recap what I've found and what I did, so I
>> don't have to type all again here ;-)
>> Ideas welcome, I'm just scratching my head. This is probably where a
>> logic analyzer is needed badly.
>> It seems to me there're unintended writes on some ram locations (not
>> so random, address wise) and it makes me think about VSP crashes on
>> C64.
>> Any idea where to look for a fault?
>
>
> Address multiplexer? I think on those boards they used the 74LS153 which
> contains two 4-to-1 multiplexer. Also check their control circuits.

yes, 4 x 153, they carry the refresh addresses and row/column addresses.
All 4 look fine, also control signals as far as I can tell.
The fault is intermittent, so it's really hard to catch with a dual
track scope. I think I'll leave this board alone
for the moment, it's that kind of fault  that really requires a logic
analyzer I'm afraid.
As far as I can remember, DRAM can be corrupted during a read
operation (or even refresh?) if addresses change at the wrong time,
right?
All corrupted location appear to have most address bits in common.

Frank

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