[vcf-midatlantic] Museum Report 2018-11-16
ethan.dicks at gmail.com
Wed Dec 19 15:31:10 EST 2018
On Wed, Dec 19, 2018 at 11:57 AM Michael Pohl via vcf-midatlantic
<vcf-midatlantic at lists.vcfed.org> wrote:
> I signed up to bring our non-working Commodore 64 to the workshop on 12
> JAN. The power light comes on, but there is no video from either the RF
> modulator or the 8 pin video jack. We ran some basic daignotics - power
> supply produces the correct voltages, voltage is present at specific places
> on the motherboard, fuse is good - but now we are stuck.
"Black screen" Commodore 64 is commonly the PLA chip. It's a
programmed 82S100 PLA that implements the memory map. Replacements
are available. You can borrow one from another machine and see if
that's the problem.
There is a smaller chance it's a bad DRAM chip. Those occasionally fail.
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