Re: VIC-II DRAM refresh

Date: Fri, 14 Oct 2016 15:36:54 +0200
Message-Id: <>
> On 2016-10-14, at 15:24, Francesco Messineo <> wrote:
>> I think I already wrote once about one case with CIA that I shall remember "forever", and which gained me a good friend too. A guy got his A2000 repaired somewhere out there from the black screen to a booting machine. But he had (I think it was printer) printer problems. So the A2000 landed on my (nomen omen) workbench. Clear case: failed bit on the port so without much thinking I pull the CIA, put a brand new one, fire the machine up, and... black screen! Hm... a failed new CIA? Another one.. the same. Maybe the machine blow my expensive chips?! No, the same CIAs work in another machine normally. And the broken CIA in another machine has the same bit broken as in the one from the customer...
>> Conclusion: a broken CIA, with broken port bit makes the machine boot normally (port bit obviously broken). A new, fully working CIA (works in every other machine normally) when placed in the computer in question makes it stop booting..
>> How's that for a Sherlock's case? ;-)
> that's even stranger than what I've seen on the C64!
> I have some suspects that the faster CIAs (6526A/B) sometimes have
> problems on some
> C64 revisions, but I've never been able to find a correlation on my
> limited set of boards.
> I've seen stock C64Cs coming with 6526B installed from factory anyway.
> Perhaps the A2000 wants a -A or -B speed grade and can't work with the old 6526?

A2000 (and other Amigas) uses the 8520 CIAs. I eventually solved the case, but I had to call the guy and tell him that I was sorry but his machine is so much of an atypical case that it needs to be given extra attention at later time and it had no chance to be ready as scheduled. We became good friends for years when I eventually repaired his machine and told him the full story.


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Received on 2016-10-14 14:00:43

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