carangil
Experienced Member
I have 3 COSMAC 1802 chips in somewhat terrible condition. (Skip to the next paragraph if you don't want the origin story) I got these years ago when I was a kid. My dad took me to the Mike Quinn Electronics closing sale (anyone in the Oakland area remember that), and I bought a cabinet of basic electronic parts to play with. It had resistors, capacitors, relays, all that, but also some ICs which I ignored. I left them in their foam. Several years later (2013 actually, because I found my forum post here when I identified these parts), I started doing electronics seriously again and took an inventory of everything I had, including this old cabinet of parts I left stored at my parents house.
At my visit to VCF West I saw a COSMAC computer there, so I decided that I should try out my 1802 chips. Yesterday I discovered the chips are in bad shape. The foam had decomposed and glued to the pins. One of them looks mostly OK. I decided to try first with the worse-condition one, assuming it is probably already trash. Trying to clean the pins, they broke off like they were rusted through or something. I could see there once was a gold plating on them, but it had pitted badly. I decided to break the rest of the pins off! It looks like the pins are two pieces, a pad sticking out of the ceramic, and the pin looks welded to it. Trying to tin the gold pads and pin stumps failed, so I filed those down too, to expose the raw silver-colored (steel?) metal under the plating. At this point I was sure the chip was probably garbage. Treat chips gently, not rubbing them against a metal file! (At least there's no static to worry about. ) That clean surface tinned well, so I soldered it onto a slightly modified 40 pin socket. I inserted this newly re-pinned 1802 into my breadboard, and wired up the free-run (hardwired NOP) circuit, and put LEDs on the address lines. Hand clocking it w/ a switch, it seems to count. I wired up a 555 timer, and now I have a free-running 1802 counting.
I suppose I need to build an ELF now! Looking online, the 'membership card' ELF seems like an easy to copy design.
Anyone have any tips on cleaning the other two chips? One of them is white ceramic, and is quite nice looking, except the pins.
At my visit to VCF West I saw a COSMAC computer there, so I decided that I should try out my 1802 chips. Yesterday I discovered the chips are in bad shape. The foam had decomposed and glued to the pins. One of them looks mostly OK. I decided to try first with the worse-condition one, assuming it is probably already trash. Trying to clean the pins, they broke off like they were rusted through or something. I could see there once was a gold plating on them, but it had pitted badly. I decided to break the rest of the pins off! It looks like the pins are two pieces, a pad sticking out of the ceramic, and the pin looks welded to it. Trying to tin the gold pads and pin stumps failed, so I filed those down too, to expose the raw silver-colored (steel?) metal under the plating. At this point I was sure the chip was probably garbage. Treat chips gently, not rubbing them against a metal file! (At least there's no static to worry about. ) That clean surface tinned well, so I soldered it onto a slightly modified 40 pin socket. I inserted this newly re-pinned 1802 into my breadboard, and wired up the free-run (hardwired NOP) circuit, and put LEDs on the address lines. Hand clocking it w/ a switch, it seems to count. I wired up a 555 timer, and now I have a free-running 1802 counting.
I suppose I need to build an ELF now! Looking online, the 'membership card' ELF seems like an easy to copy design.
Anyone have any tips on cleaning the other two chips? One of them is white ceramic, and is quite nice looking, except the pins.