On Fri, Oct 14, 2016 at 11:26 AM, Gerrit Heitsch <firstname.lastname@example.org> wrote: > On 10/14/2016 11:15 AM, Francesco Messineo wrote: > >> What if you would find a Fujitsu DRAM chip bad among the 8 on a board? >> All with the same datecode? > > > I'd change the failed chip, so far only the MT4264 have shown that 'if one > fails, others will follow' pattern when it comes to RAMs. well, I'm really interested in numbers to be a believer :) I guess you have records of how many RAM chips have you seen and how many were bad. I didn't keep track of that (unfortunately, but I started when these things didn't really matter). If I have to think about recent (from year 2000 to now for example) repairs, I've never happened to find a C64 with more than 2 DRAM chips bad out of 8, so the batches are reliable enough. If we see that 7 chips out of 8 works fine after so many years, what we conclude? > > And removing chips that I know are bad or that I don't care about (cheap > TTLs) is easy enough. Cut off all pins at the IC, then desolder all pins, > clean the holes, add a socket. yes, sometimes I use this method too, but a desoldering station is almost as fast. >> >> >> yes, I've changed quite a few of them. On the other hand, my >> collection shows more 7707 failed than 7708. I still have 7708 and >> 7709 working, no 7707 working left that I'm aware of (maybe inside >> some 1541/SX-64, I didn't check very well on those). > > > The 7707 is the 7406 replacement. One of the drivers has to work against a > 180 Ohm pullup and most of the rest is directly connected to the outside > world. I'm not surprised that those fail easily. The original 7406 goes bad > often enough. I've had one failure on a regular 7406 that I can remember... pretty reliable against the 7707 failure records :) > > >> Most of the CIAs in my collection would "boot" fine in a C64 though, >> they have one or two bad bits in the ports. > > > I have 2 CIAs that when used together in the same system will fail the diag > test. But if combined with other CIAs will show no problems. indeed, at least 4 or more of the ones I have fails a diag test on some systems and not on other ones. I've been always wondered why. I've never found a possible explanation so far. Anyone? Frank Message was sent through the cbm-hackers mailing listReceived on 2016-10-14 10:00:58
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