Dead PET4032

[tony duell]

> 
> 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