Slightly OT: RAM for Commodore PET

DarrenF

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I'm working on a Commodore PET computer (Model 2001-8) for a friend. I've identified a bad RAM. I boots and runs fine, but now I only have 7K, vice the original compliment of 8. I'd like to return it with a full deck of RAM. However, the only source I've been able to find wants $15 each + shipping.

Anyone happen to have any 6550 RAM (MOS or MPS marking) ICs they're interested in selling?
 
What is the full part number on the chip? I might be able to cross it.
You can also check with channelmanic, I think he works on alot of the old computers.
 
GOOD LUCK!

I have 5 here but have a PET to repair. It took me a long time to find the ones I have.

6550 is an ODD duck that was produced for a very short time and it has clock signals to synchronize it. It's very difficult to find and took me 6 months of scouring to find the 5 I have here.
 
Thanks, guys. I wouldn't have posted if it was easy to find ;)

AFAIK, it was only ever used in the Commodore PET, but this could be incorrect. I'll look at it tomorrow to get the exact and full part number printed on it.

Hamster: Well, the "dual 6550 adapter" is specifically designed for the video pair of RAMs. I suppose I could use than, which would net me those two good 6550s to use as main system RAM. The "6502 RAM/ROM expansion" would eliminate the need for all system RAM and ROMs entirely. In either case, his order page is gone, and buying custom PCBs from Germany has got to run $50 or $100.

Looks like maybe the guy selling them on ebay for $15 ea isn't such a bad deal after all...
 
the eagle files are there, you can make your own pcb :p or use sparkfun's pcb batch program. (ie, you give them the files, and when they have room on a pcb run, they stick your in there and you get them)
 
I'm pretty sure I'm going to just buy a RAM or two, but that sparkfun batchpcb thing sounds pretty cool. $15 for a a single 2 in^2 PCB sounds quite reasonable to me.

I guess I need to get Eagle and learn to use it. The only PCB I've made was single-sided and I etched it in a plastic tray in the garage...

the eagle files are there, you can make your own pcb :p or use sparkfun's pcb batch program. (ie, you give them the files, and when they have room on a pcb run, they stick your in there and you get them)
 
Just a brief follow-up on this year-old (today) topic.

I had the PCB that Hamster linked above built from the provided Eagle file. (At BatchPCB, before they shut the doors.) I didn't have any surface-mount 74LS00, so it sat around until I finally remembered to order them. Parts showed up last week, and this weekend I finally assembled the thing. Put in a 6116, removed the two MOS6550 video RAMs, and plugged the module in their place. Works like a charm, so I installed those two 6550s in the main RAM bank, and now have a full compliment once again.

I have two extra PCBs and 74LS00 SMDs. They're available on the off chance someone else is working on a PET and could use them.
 
Picture of the installed module attached.

Note position of the 6116 in the 28-pin socket. If you use a 28pin RAM, there's a split pad that needs to be changed. Threre are also holes in the PCB to allow installation of a 0.3" wide socket/IC on top instead of the 0.6" I used. I used a strip socket instead of a regular socket, to make assembly easier.
 

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Picture of the installed module attached.

Note position of the 6116 in the 28-pin socket. If you use a 28pin RAM, there's a split pad that needs to be changed. Threre are also holes in the PCB to allow installation of a 0.3" wide socket/IC on top instead of the 0.6" I used. I used a strip socket instead of a regular socket, to make assembly easier.

Very nice! I put in a recent order to OSH for some custom Atari 555 paddle replacement boards. I'm interested to see if the quality has changed since BatchPCB sold. I placed an order a few years back for some custom header adapter boards, and half of them came back with errors. Before I realized it, with the one board I built up the traces didn't run to the footprint vias, and I ended up having to magwire 60+ connections. Not fun. :(
 
i used expresspcb , and ordered 100+ boards, i was actually impressed with the speed and quality of their work, yes, price was a little high, but they give you great options on ordering.
 
Mine came out purple with gold flashing. Interesting.
 

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