5 Oct
2015
5 Oct
'15
1:40 p.m.
----- 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.
A
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
sort.
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
clue.
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.
Good luck!
m
On 5 October 2015 at 16:55, tony duell
<ard at p850ug1.demon.co.uk> wrote:
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home
computer collection?
www.binarydinosaurs.co.uk
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
warble.
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
DRAMs?
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
-tony