5 Oct
2015
5 Oct
'15
11:52 a.m.
Look for inconsistencies in voltages and pulses to and from RAM. You may
need RAM at the lowest memory locations to boot. Hooking up the keyboard
at least to eliminate a missing keyboard as a reason the system does not
boot, and you can issue commands to search a disk drive even if the display
is faulty. At least if you have a IEEE drive attached you can watch for
the the drive to respond when the 4032 is powered on, for signs of life
from the computer.
On Mon, Oct 5, 2015 at 1:40 PM, Mike Stein <mhs.stein at gmail.com> wrote:
----- 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,
--
Bill
vintagecomputer.net
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