PET stuff

Does anyone out there know much about the old PET 2001 machines? I received a PET a couple of years ago, in which all of the 6550 SRAMs were fried. I replaced them with the chips from another PET 2001 (one with the miniature keyboard, from 1977) and the system worked fine. Does anyone know how all of the memory chips could've been killed? I tried them in various patterns in the sockets, and it does seem as if all 16 of them are fried. Anyway, is it still possible to get 6550s anywhere? And if not, is there a replacement that could be used? Even better: Can I simply replace the 6550s with another type of chip and get more RAM in the system? Most of my software works in 8K, but I do have some music files that require more. (I have one of those external music boards that plugs into the cassette2 and user ports, that delivers four voices.) Now, another question. With that same PET, came an expansion board of some kind. Its like a daughterboard, physically mounted on posts above the motherboard, but connected via the memory expansion connector on the side. It appears (yes) to be a memory board, with 16 RAM chips on it. At least, they look like they could be RAM chips, judging by the traces on the board. However, I've never seen RAM chips with gold contacts and gold plates on their backs before, as six of these chips have, so I'm wondering if this could be more than just a memory board. The board is dead, BTW. The PET won't operate with the board plugged in. It just comes up with a screenful of garbage characters. The board plugs directly into the PETs power supply, and then a cable leads from it to the PET motherboard's power connector. There are three large 470uF capacitors and two things that I guess are voltage regulators (I don't know much about electronics :) ), so I'm guessing that this board has its own refresh circuitry on it and it uses DRAM, but that could be totally wrong. :) Both connectors on the cable that leads from the expansion board to the motherboard are noticeably burnt. In both cases, the burn marks surround the pin that connects to the black wire. The only identifying mark on the board is the text: R 3014 rev. C COPYRIGHT 1978 R.C.Factor Does anyone have any better guesses than me as to its function? (Can the edge connector on the side of the PET be used for anything other than RAM expansion?) Doug Spence ds_spenc(a)alcor.concordia.ca