PET problem SOLVED!

Ethan, Dwight (and anyone else who helped), Thanks for all the help - I've solved it and it works! Turns out it was NOT the ROM's -- After my last post I got to thinking that the PET ROM's are probably fused type, and wouldn't go marginal like an EPROM, so I focused on the RAM - sure enough, testing again, and I found that bit 1 of location $11 was stuck at zero (I'm positive I tried it before and it seemed to work - bit the funky PET monitor with it's exact # of spaces required was causing me some grief!) Anway, when 01 got incremented, instead of 02, it got 00 - this was hanging the search for end of RAM, which never incremented the high byte and therefore never traped at 32k.. Checking the Schematic, bit 1 of the low memory bank is U17 - pulled it, put in a socket (always!) and stuffed another 4116 - voila!!! it came right up! Also figured out the startup "noise" mystery (such unanswered questions "bug" me), turns out the PORTA bit 7, which is used for the DIAG input is also used to control the speaker (it was right on the schematic once I looked for it - duh) - pulling this line low disabled the speaker. 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