[vcf-midatlantic] Workshop this weekend - Thoughts?

Jeffrey Brace ark72axow at gmail.com
Sun Jan 31 09:46:58 EST 2016

Would I simply look on the PLA chip and find 82s100 on the top imprinted

On Sat, Jan 30, 2016 at 6:27 PM, Jonathan Gevaryahu via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> Another question related to this:
> If anyone has an older 'breadbox' c64 (not c64c) with the signetics 82s100
> PLA in it (only used for the first year or so before being replaced with
> the MOS PLA) let me know, I'd like to try to read the fusemap out with an
> 82s100 programmer. There exists a reverse engineered fusemap of the 82s100,
> but it was done "by hand" using an eprom programmer to probe all the inputs
> and look at outputs like a giant truth table, and based on an interview
> with Bil Herd a few years ago, I now know that this will not produce an
> accurate dump of the chip, because the engineeres at commodore played some
> tricks by adding extra/unnecessary gates to certain outputs to
> intentionally 'slow down' the edges of certain signals to prevent glitches.
> On 1/29/2016 5:49 PM, Jeffrey Brace via vcf-midatlantic wrote:
>> Chris,
>> I was wondering the same thing. I would say from experience with repairing
>> Commodore 64s at the workshop, I would bring 5-10. Some you would use for
>> parts, but I would expect at least 5 can get fixed. But this workshop is
>> unusual because we got a lot of people that know their stuff coming to
>> help
>> and lots of people working on fixing. If you want to bring 20, that is
>> great. I wouldn't expect all to get fixed, but there is a great
>> possibility
>> that they can. For myself I will bring 5 working drives, and 10 non
>> working
>> drives. Some of them I have labeled as to the dysfunction with a post-it
>> note. I don't have a lot of experience fixing them, I have tried cleaning
>> some and they remained unfixed. My gut tells me that a smaller percentage
>> can be fixed with cleaning them 10%, a bigger percentage could have chip
>> issues like 25%, maybe 50% have component issues (capacitor, resister
>> etc.), another 15 percent are disk head or speed issues. What does
>> everyone
>> else think?
>> Jeff
>> On Fri, Jan 29, 2016 at 12:15 PM, Chris Fala via vcf-midatlantic <
>> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
>> I have been really looking forward to an opportunity to get some
>>> experienced assistance repairing 1541 drives. I acquired several on eBay
>>> and other sources over the last couple years. Some were functional, some
>>> worked after the heads were cleaned, and some are still malfunctioning
>>> for
>>> unknown reasons. I haven't had the time to dig deeper and diagnose the
>>> problems on these. I hope that I can learn more about these this weekend
>>> and get at least some of this last category working.
>>> Practically speaking, how many drives should I bring this weekend? Is 20
>>> too many or is it possible to actually work on that many in a day? Are
>>> there common problems that can be addressed quickly, or is it more likely
>>> that each drive will require unique troubleshooting?
>>> .
> --
> Jonathan Gevaryahu
> jgevaryahu at gmail.com
> jgevaryahu at hotmail.com

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