I bought an Apple IIc off ebay recently and it was advertised as having memory issues as a lot of these machines do. I ordered the ROM chip that contains the self-test code and made the necessary mods to the motherboard so I could self-test the RAM chips. When I did, it said that aux RAM chips 0, 2, 3, and 4 were bad. I've replaced all the RAM chips with sockets and tried a couple different vendors online for replacement RAM chips. No matter what I do I can't seem to get it to pass the RAM test or show different results. I've swapped chips arounds and it doesn't follow the chips. It seems to be the board itself. How can I narrow this down further? I'm confident in my soldering abilities. I've done a fair amount of it in the past. I've gone back after the fact and re-soldered chip sockets and it doesn't make any difference. I've never used an oscilloscope and I wouldn't know how to read/interpret it without someone explaining it to me.
How can I get this poor, old decreipt machine to run Aztec, Hard Hat Mack, and the original Mario Bros. once again?
Assuming you have a continuity or multimeter tester, you should start by checking all of the bad RAM pins for connection to the corresponding pins on a good chip. Within each bank (MAIN and AUX), every pin except 2 and 14 should be connected to every other chip. If that doesn't show any issues, then you need to check pins 2 and 14 of each chip back to the data buffer chip at position E11.
If all the continuity checks pan out, then possibly UE11 is bad or there is some other shorted or broken trace.
Edited / Disregard, see Jeff's post above.
Thanks for the tip! I checked the connectivity and found some broken traces between ARD2 and ARD3. Pins 5, 12, and 13. I think I damaged a couple of the traces when I removed the chips. I stole some very fine wire from an old USB cable and jumpered the pins. Everything seems to work fine now. Thanks for the help!!