Apple IIc RAM Replacement

As part of restoring an Apple IIc I decided to test the RAM since I've experienced some unexplained freezing when testing.

First I used the floppy based RAM test utility found here and it actually reported a bad bit 7:

My Apple IIc had the original 0xFF ROM version, but I wanted to upgrade to version 0x04 so I could run the built-in diagnostics to double check. Upgrading the ROM involves some hardware modifications that are explained here.

Sure enough, after entering built-in diagnostics with the new ROM it reported:

*RAM    1 0 0 0 0 0 0 0
          

The star means it is the auxiliary RAM, and once again bit 7 is marked with a '1'. This means that the chip at location "ARD7" on the mainboard needs to be replaced.

After some deliberation I finally ordered some "new" 4164-15 RAM chips from a random seller at eBay. The chips failed the acetone test, meaning they have been re-badged and are possibly fake:

I decided to test them anyway and replaced the old RAM chip with a socket:

Luckily the re-badged chips works and both RAM tests pass. Notice that the old chips are of the dreaded MT branding which are known to fail a lot.