25 Oct
2002
25 Oct
'02
6:17 a.m.
Thanks for the tips. I have a logic but working scope right now (there's one
up in MN in one of the storage units).
----- Original Message -----
From: "Ethan Dicks" <erd_6502(a)yahoo.com>
To: <cctalk(a)classiccmp.org>
Sent: Friday, October 25, 2002 9:25 AM
Subject: Re: Pet Question
--- Keys <jrkeys(a)concentric.net> wrote:
Tried my Pet 2001 series today and no display? If
I turn the bright up
all the way I can see white broken lines across the screen. The built
in cassette players comes on fine. Anyone have clue where to begin?
Do you have an oscilloscope? A logic probe? Knowing what tools you
have helps direct the assistance.
Check for a reset pulse on the CPU (or any other VLSI chip - it's the same
signal). Check for clock to the CPU. One of the chips (I think it's
the 6522) has to work or the video is permanently blanked (i.e., if you
remove it entirely, the machine runs as best it can, but you'll see
nothing). If it's nothing that basic, it might be a component fault
in the video circuit. Since you mention it's a "2001" - that means
that there is no 6545; the video is in TTL. The schematics are at
http://www.funet.fi/pub/cbm/schematics/computers/pet/index.html - pick
the right link for your model (static PET vs DRAM-based-no-CTRC)
Oh... check the voltages first. ISTR there are two +5VDC regulators.
One failing can cause all sorts of unhappy behavior.
Cheers,
-ethan
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