When you say "powers up fine", do you mean: - Powers up and runs - ie, even though the screen is garbled, you can see characters changing where the ready prompt would be if you press RETURN a few times. (in this case - according to your description, you should see every other character from data output to the screen?) - or - - Powers up and does not catch fire, smoke, blow fuses, but otherwise does not show signs of life. If the former, then cause is most likely display RAM - I've had display rams go in a couple of PETs over the years (iirc they are 2114s). If the latter, the problem could be that the CPU is not getting far enough to clear the screen or going haywire and overwriting the screen at some point in the startup process. Standard debugging - I've had bad DRAMs, ROMs and the odd buffer chip fail in various PETs at various times - shouldn't be too hard to track down. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html