[vcf-midatlantic] Workshop this weekend - Thoughts?

Jonathan Gevaryahu jgevaryahu at gmail.com
Sat Jan 30 18:27:25 EST 2016

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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