5 Oct
2015
5 Oct
'15
9:27 a.m.
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
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