ROM Verification

Bad ROMs are seemingly a common cause of failure on PETs, so whilst waiting for the supplies I'd ordered for repairing the PCB, I thought I'd try to verify the ROMs' contents. This PET had four original ROMs and one as yet unknown third-party expansion ROM. As you can see, most were the standard black plastic affair, but there was one lovely purple and gold one at the end. They don't make 'em like that any more!

The ROMs on the motherboard.

My cheap and chearful EPROM programmer didn't take the MOS 6316 and 6332 ROMs directly, but their pinout is similar to more common 27xx parts. It therefore wasn't too difficult to build an adapter with which to fool the programmer it was reading a 2764. I got a bit impatient trying to solder the pins together neatly, so it's not the neatest job, but I figured it'd do - something that would come back to bite me later!

Simple adapter was built from IC sockets.

Adapter fitted to the EPROM programmer.

I set up the programmer and its software and took dumps of all the chips. At first glance, they looked fine. Most of them contained at least some text which showed it wasn't just random junk being pumped over the line. On closer inspection it turned out there were some discrepencies when compared byte-for-byte with the known-good images I downloaded here . What's more, I'd get different results from one dump to the other. It was however obvious that all the correct data was in there, as what was incorrect in one dump was fine in another. At this point I figured it was down to my rather hackish set-up and considered the ROMs good.

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