From: William Levak (wlevak_at_grex.cyberspace.org)
Date: 2006-05-01 07:05:24
On Sun, 30 Apr 2006, Anders Carlsson wrote:
> There is a 74LS86 at UD6, but maybe it is functionally equivalent? Anyway,
> using my multimeter there seems to be signal from pin 39 on the 6545 to
> pin 1 on the UD6 chip, From pin 1 to 3 there seems to be a signal, but
> with 1.7 kOhm resistance?
That could be a 74LS86, the schematic isn't very clear. Do you have a
signal on pin 3 of UD6 relative to ground? If so you should have sync,
but not necessarily the correct sync. This is set when the registers of
the 6545 are loaded.
> I tried to lift the 324744-01 PLA, but then the computer refused to start.
> I also noticed one pin on the character EPROM (yes, this is a localized
> machine like all the other PETs) was bent, so I lifted and reseated it,
> with no improvement. Maybe pin 24 is not supposed to have contact anyway?
Pin 24 is +5V, without this you don't get any characters.
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