Replacing bad RAM ICs on MVS 4-Slot

I have a 4-slot MVS board that on boot was giving a work RAM error. Referencing a thread here and this wiki page, I determined the IC at G9 was the culprit. Ordered a couple replacement chips.

Tonight I replaced G9. On boot, I instead got a backup RAM error in the lower bits. So I replaced F9.

Booted back up, and now I get a backup RAM error in the upper bits, so seemingly I need to replace D9.

Replacing the chips isn't too bad and I can order a couple more, but is having multiple RAM ICs fail indicative of some bigger problem? They seem to be failing in order so I'm hoping D9 will be the last RAM IC that needs to be replaced.

It's common to find the upper and lower failing at the same time on the backup RAM section. You might find that the backup RAM is OK but you've got a problem with write enables or output enables or something. Have you used SMK Dan's diagnostics ROM?

That's a good idea. I hadn't encountered a need for it until now. I'll see if I can find one locally that can burn one for me.

Still waiting on diagnostic ROMs. Should have them next week. In the meantime I got a few more replacement RAM chips. I removed the IC at D9 and in the process, lifted a pad. Followed that trace and ran a wire to the destination.

Now when I power on the board I hear a clicking noise over and over, and a garbled colored screen that seems to be repeatedly restarting. Wondering if I jumped to the wrong spot, I removed the jumper wire and tried again, and get the same result. At this point I'm not sure if I fucked something else up that has it failing before it gets to the RAM tests, or if those errors are now fixed, and its failing as a result of something else.

I would suggest verifying you don't have any bridges on the ram chips you just swapped. From your image it almost looks like there could be one between pins 10/11 where you added the wire. I tried bridging those on my test mv4 and got similar symptoms to your video.

If there arent any bridges I would then check continuity between ram chip pins near where they go into the chip itself and the underlying pad to make sure you have a good connectivity.

Confirmed there's no bridge between those pins. Tested continuity for all of the pins on that chip placing one probe on the pin, then running the other lightly along legs of nearby chips. Two oddities.

One pin (7th pin on the top of the chip), I couldn't find what it went to. I found the hole (that's the technical term, right?) that it went to on the underside of the board, and traced it to another hole back on top of the board, but wasn't able to follow to its destination because I'll need to clear away some of the foam padding on the bottom of the board.

The second strange thing I noticed was with pin 8 on the top. I found two points of continuity on the chips below. The first is on a chip directly below it on the board, and the second is down toward the bottom of the board, and to the right one column. Not sure if that's normal. Maybe it happened on other pins too, but I didn't notice because I stopped after finding the first point of continuity.

Still a ways to go in tracing the pins on the other chips I replaced, but that's where I'm at so far.