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 Message was sent through the cbm-hackers mailing listReceived on 2018-02-20 19:00:07
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