Some months back, I picked up a 1GB DIMM at a computer fair. It was cheap, which was about the only thing going for it, but I thought I’d take a chance on it. When I got home I plugged it into my PC, and it all started going horribly wrong. Needless to say, a few minutes later I was running memtest+ and finding millions of errors.
Given the sheer number of errors, I believed it must be something physically wrong with the wiring, most likely a badly soldered chip. So I resolved to take the DIMM into work and inspect it carefully under a microscope and reflow anything which I found to be dodgy. In the end I didn’t get round to doing that, but I did at least have a peek at it under a magnifying glass at home. After concluding that the solderwork wasn’t great but was probably good enough, I suddenly realised that I was missing the obvious. There was no fault with the soldering of the RAM chips. In fact, the fault appeared to be with the PCB manufacture. Pin 2 was entirely missing. There was no copper on the PCB where the pad should have been. I looked up pin 2, and discovered that it’s Data 0. Well, that nicely explains all those memory errors.
After a not so quick shopping trip, I ended up with some silver conductive paint. After several attempts at getting the paint just in the right place and scraping the excess off with a scalpel (finding a brush fine enough for this kind of work is really hard) I ended up with a brand new pad for pin 2, which connected nicely with the PCB track end that would otherwise have connected to the copper pad.
I left it to dry for a while (about as long as it took to find that memtest+ CD), and then plugged it into the PC. Amazingly, memtest+ didn’t report any errors for over 40 minutes (until I got bored). I fired up the PC, and everything was happy. My PC now has 1GB more memory.
Was it worth it?