On 19/06/2020 5:48 pm, Gerrit Heitsch wrote: > On 6/19/20 11:23 AM, Clockmeister wrote: >> >> >> On 19/06/2020 4:00 am, Francesco Messineo wrote: >>> On Thu, Jun 18, 2020 at 9:49 PM Gerrit Heitsch >>> <gerrit_at_laosinh.s.bawue.de> wrote: >>>> Yes, but often, if you have a dead C64 with a lot of 77xx chips on it >>>> it's one of those that is the problem (unless it's the PLA, but >>>> that is >>>> also known as '7700-xx' or '8700-xx'). >>> I've repaired dozens of C64 :) >>> Once I've found a C64 that had almost all 77xx logic chips and one by >>> one I had to change them all to revive it. >>> I don't desolder parts before making sure they are really bad usually. >>> I've never said they're reliable, but they aren't either all failed by >>> now for sure. >>> >>> What is really "disturbing" in the MOS reliability issue is that it >>> appears to depend on the part number too. >>> Either some parts were made in different farms, so the less reliable >>> farms were producing the less reliable part numbers >>> or it was heat-related maybe (like the hotter parts failing more >>> often)... >>> I tend to believe it was a "farm" issue. >>> >>> Frank >>> >> >> Sorry Frank my previous replies were meant for the list not just you >> by email, apologies for that. >> >> C64 DRAM has a high failure rate but that's true of DRAM generally in >> all my vintage equipment these days it seems (yes some brands fare >> much worse like mT). I rarely had to replace was the 77xx logic on >> any Commodore computers though, I would say about the same rate as >> for other systems that used 74XX logic. > > I had a lot more dead 7708 (74LS257), 7709 (74LS258) and 7707 (7406) > than their 74xx equivalent. > > There you go. Not my experience but clearly a pattern there in that event. >> It is however my opinion that power supply ripple, not only over >> voltage is quite capable of damaging IC's in the long term including >> DRAM and C= supplies were notoriously rubbish back in the day and >> haven't gotten any better with age. > > A 78S05 (as used in the C= supplies) doesn't produce much ripple > though, at least as long as the large capacitor in front of it is > still within spec. You get a lot more from any switching regulator. > > Gerrit > > It's the capacitor that is the issue. On the potted supplies there isn't much option to fix that issue which is why they are only suitable for the bin.Received on 2020-06-19 15:02:06
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