mhs.stein at gmail.com
Mon Oct 5 12:40:40 CDT 2015
----- Original Message -----
From: "Adrian Graham" <binarydinosaurs at gmail.com>
To: "General Discussion: On-Topic and Off-Topic
Posts" <cctalk at classiccmp.org>
Sent: Monday, October 05, 2015 12:27 PM
Subject: Re: Dead PET4032
> Hi Tony,
> The screen's not connected, nor keyboard. I
> figured there was no point
> until I got a chirrup.
> My logic tester is a cheapo Micronta, yes.
> There's an unpopulated ROM
> socket at UD11 so I can easily get +5 and GND
> from there for probing, I'll
> do that tonight.
Is UD11 the only empty socket? If there's a chip
in UD12 I'd remove it in case it's defective or
has bent pins etc.; it'll be an option ROM of some
Tony's right about the CG; it's not directly
connected to the data & address busses so it's not
likely to hang the system unless it's pulling down
Vcc. I would connect the monitor though instead of
just relying on the buzzer for signs of life; if
there's any display at all it might give a useful
I'd also check UD7 for poor contact or bent pins
Finally, I'd ask on the Vintage Computer Forum;
even without me (;-) there are some very
knowledgable PET folks there.
> On 5 October 2015 at 16:55, tony duell
> <ard at p850ug1.demon.co.uk> wrote:
>> > One chip that does get hot is the Character
>> > Generator at UA3 which I was
>> > going to swap with the one in my other 4032,
>> > but that doesn't power up
>> > either. Presumably I can borrow one from a
>> > 3032 or 8096?
>> A machine with a dead character generator ROM
>> (unless it is so dead as to
>> pull a power supply line down) will still
>> initialise. You would get the
>> And I would be surprised if you got nothing on
>> the screen either. Odd bit
>> rot would mean the wrong patterns for some
>> characters. But still something.
>> This is presumably a large-screen machine with
>> a 6845 on the mainboard.
>> Is it initialising that (look at the vertical
>> and horizontal sync outputs
>> with your
>> logic probe, are they toggling)?
>> Is it accessing the kernal ROM? Is the CS/ pin
>> pulsing low?
>> What about the RAS/ and CAS/ signals on the
>> > A lot of the repair pages use a piggyback
>> > 6502/ROM/RAM add-in called a
>> > PETvet but all I have is a DMM, logic tester
>> > and other working PETs as
>> > sources of chips I can borrow.
>> I assume the logic tester is a simple logic
>> probe and not a logic
>> analyser, alas
> Owner of Binary Dinosaurs, the UK's biggest home
> computer collection?
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