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 <a...@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
