I decided to try repairing the original front memory that quit working.
Here are rust stains in the front cover from the memory board shield showing that it was under water.
There are 8 ceramic capacitors and one tantalum capacitor on the board. They all tested good.
I don't have a way to test the memory IC's so I replaced all of them. To my surprise it is now working.
Here's the repaired board with one of the old chips in front.
The reason I was surprised it worked was because of a mistake I made. Removing the IC's is difficult because I didn't have enough room to clip the leads. That meant heating all of the leads at the same time to remove them.
So I used a hot air rework station to do that. However when they designed the board they used thermal reliefs where needed except for the power planes where they connect to the IC. Without a thermal relief the ground plane sucks the heat away and makes it difficult to melt the solder on both sides. So you have to get the board hot enough to melt the solder.
To do that I first baked the board at 90 deg C for a couple of hours.
You normally should bake a board to remove the moisture when using a hot air rework otherwise the steam can create very high pressure inside the IC's. Especially for moisture sensitive ones.
That was the mistake. I should have baked it at 125 C for 48 hours. There was more moisture absorbed into the PCB that I realized.
So the board blistered in one spot as you can see on the right side of this photo.
I was fortunate that it didn't break any vias when it blistered. I'm happy it works in spite of my mistake.