RE: Static PET repair (was Re: VCF PET Alive! - April 24th to May 2nd)

From: M H Stein <>
Date: Tue, 30 Mar 2010 05:21:34 -0500
Message-ID: <01CACFC9.609C1BA0@MSE_D03>

They looked like pretty straightforward repairs initially; that's what you 
get for testing too much ;-)

Maybe this do will inspire you to get them off your bench; good luck.
Sorry if the one I sent you turned into more of a project than you


From: 	Ethan Dicks[]
Sent: 	Monday, March 29, 2010 3:57 PM
Subject: 	Static PET repair (was Re: VCF PET Alive! - April 24th to May 2nd)

On Mon, Mar 29, 2010 at 5:36 PM, M H Stein <> wrote:
> Don't tell me you still have Philip's PET?
> ;-)

OK.  I won't tell you.  ;-)

I've fixed the PSU section on the one board (bad diodes, as was
discussed on the list), but there appears to be some additional stuff
wrong, possibly an address or databus buffer ('240 or '245 or the
like) based on some initial behavior observed with a Fluke 9010A and
6502 pod.  I'm hampered by the fact that the PETs from this era
(unlike my later 32K PETs) have sockets with a shoulder that
interferes with solidly seating a machined-pin socket in the CPU
socket.  These double-wiper sockets admit a DIP chip just fine, but
not a machined-pin.  I'm not even sure what the correct description of
them is - I've never seen them in any other board before.  I did some
initial testing by plugging my Fluke into a wire-wrap socket, then
holding the socket steady against the exposed inner faces of the CPU
socket pins, but it's not a mechanically steady arrangement - if I let
go, there isn't enough back-pressure to hold the wirewrap pins in

The other board (with 6540 ROMs and 2114 SRAMs and the broken Japanese
CHRGEN ROM) passes all RAM tests (and does come up with the BASIC
splash message), but still locks up on cassette operations.

The board I got from you produces $FF garbage in video RAM (not the
expected random characters), and has the additional fault of the video
timing pulses being "wrong" (the image is short and squeezed so much
left-right that it wraps).  Other 9" PET boards in this 9" chassis
display the right thing, so I'm looking for a "bad" 74107 or 7474 in
the timing chain - i.e., some clock isn't getting divided down enough


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Received on 2010-03-30 10:00:03

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