At 14:41 29/09/2005 -0600, you wrote: "Most everything" about the PET is at: http://www.funet.fi/pub/cbm "Garbage" characters at startup usually mean the machine isn't clearing the screen, which is part of it's startup initialization. Possible causes - The processor isn't running... Look for apropriate 6502 clocks. You should see a fetch to the top of memory (FFFC-FFFD) as the first access (CPU fetches reset vector), and then fetches at whatever address is stored there. - The code is invalid... See notes on PET ROMs below. Could also be a bad buffer etc. If the ROMs are correct, then look at each data line to insure that it is making it all the way back to the processor. - The processor is "crashing" before it gets there. Most likely cause bad-RAM (stack failure). - The code is getting "hung up" waiting for something --- not much happens before the screen clear, but it might be this ... if so, you should be able to scope the address lines and see the code sitting in a tight loop - you should also be able to figure out what it's polling (read address) and using the schematics, memory maps, listing etc (avail from funet) you can figure out what is wrong. (I had one unit which hung polling a bad 6521). I've repaired about 1/2 dozen different PETs over the last couple of years, and here's what I found (in rough order of most common to least common): #1 - Bad connections, ROM sockets and power connector to mainboard (some level of this in almost all the machines I worked on) #2 - Bad 2114 SRAMs (3-4 instances of this - also in 2040/4040s) #3 - Bad 4116 DRAMs (3-4 instances of this) #4 - Bad ROMs (2 instances of this) ** #5 - Bad 6521 (1 instance of this) ** ROMS: You can get the ROM images from funet - Exact compatible EPROM devices to the commodore ROMs are tough to find - If you are lucky (as I was in one instance), and the bad ROM is the Edit ROM, which is only a 2K device, you can actually replace it with a 2116 (It doesn't quite line up - (IIRC it gets SELECT on OE, and SELECT gets driven by an address line which is low for the 2K "bottom half" of the socket range where the Edit ROM lives) but it's "good enough" to work). For the 4K device I replaced, I had to make a little daughter card (see photo in my PET section). I checked the ROMs by making an adapter to read them in my homebuilt programmer as 2732s, and compared the results to the ROMs from another PET (you can use the images from funet). Depending on which version of the ROMs you have, you may be able to get into an internal monitor by pulling down the DIAG line - but I think the screen clears before it is checked - again, you can find the pinouts on funet. I also have complete scans of the 2001 manuals posted on my site which shows the I/O ports and pinouts. Good luck! Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html