PET startup sequence?? (was LF: Commodore PET schematics, troubleshooting info)

Hi Dwight, I've checked all the RAM signals - everything looks OK (about the same as the other unit). I tried putting my diagnostic jumper on both the other (working) SP9000 and the PET 4032 that I have here, and both of them exhibit the same problems with getting the monitor up and running - so I think those issues are just a red herring and are not realated to the actual fault. (For some reason, entering 'M 6666' seems to cause a "break" which comes back with SP=FF and from then on it works OK - on all three machines). I haven't seen a RAM error yet in my poking around (and I've done a fair bit), however there could be address bus errors etc. which I would not see. I really wish I had a better way to load code into the machine then through the keyboard - I may still do up a RAM test replacement for the kernel ROM. (Which is a big job, since I don't have a plug-in replacement for the 2332 so I need to make up an adapter etc.) Has anyone created a "virtual" tape deck? - The monitor has commands to load and save memory from/to tape... I'm still trying to fathom what exactly is happening at power-up - I can't explain the timing of the "beep" - I thought it might bave been generated by the interrupt, however with pin4 physically pulled out and tied high (no IRQ) the beep still happens... I think the key to understanding what is going on is to figure out exactly where it's hanging during the initialization of BASIC. Btw, if I hit 'X' at the monitor prompt, I do get the BASIC 'READY' prompt, although you can't do anything due to the fact that in this case, BASIC never got initialized ... Same thing happens on the other machines. Argh... this is turning into a bigger job than I had expected (It's a lot easier when things don't work at all) ... I want to get these d*mn things off my bench - I acquired a 5100 earlier this week which is has been calling to me ever since I brought it home. Regards, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Vintage computing equipment collector. http://www.parse.com/~ddunfield/museum/index.html