Re: Desoldering Apple IIc RAM chips

[David Wilson <mcs6502@gmail.com>]

> I simply soldered a working ram IC over the existing one,
> and they work just fine. I know, it doesn't make sense
> to me either, but I tried it and it works. Haven't had
> any ram problems otherwise with the IIc.

Depending on the type of RAM fault, I can see how that might work.


I just de-soldered another RAM chip. This time I made sure the holes
were all solder free and levered one side of the chip up with a fine
screwdriver. It released without damaging the board. The biggest
problem was that the IC pins were bent to hold the chip in place
before they were flow soldered. I had to straighten them with a
regular iron before the the de-soldering iron would make a good seal
prior to sucking.

I was able to identify the bad chips because of the spurious
characters on the screen. This one had " chars indicating MRD1. The
other had $ and ( indicating MRD2 and MRD3. After replacing MRD1 I
also upgraded the ROM the from original (FF) to ROM 00. Running the
self-test now indicates yet another faulty chip - this time in Aux
RAM. Good thing I have not screwed it back together yet.

I am just about to run out of spare 4164 chips. It looks to me that I
can use 41256 chips instead - the IIc just ties A8 to +5V. Has anyone
else done this?