Dead PET4032

[Adrian Graham]

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:

> >
> > 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
>



-- 
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk