Working on a replacement CPU board

Well, here we go. I bought an old, untested CPU board on ebay quite a while ago. It clearly had some battery leakage problems that had been cleaned up by the previous owner, so now I need to fix the rest and get it up and running again.

Step 1: asses the damage.

The CPU board when I received it

I noticed some of the copper was missing where the IC fittings used to be, so I first started with measuring the tracks that were still there. A lot of them are broken and not making the right connections. The breaks were too big to fix by covering them with a bit of solder on the component side of the PCB, so I will need to run wires on the solder side of the PCB. But first, I put in the missing IC fittings for the RAM chips.

Next I removed the 24-pin IC fittings for the three 2532 EPROMs. I replaced them with three 28-pin fittings so I can put in two 2764 EPROMs, which are needed to use David Gersic’s Freeplay ROMs and are much easier to come by. Using three fittings still gives me the option to put in the original 2532 EPROMs if needed. This also involves changing the jumpers just above the EPROM IC fittings.

As I am not going to reuse the IC fittings, I just cut them off.

Cutting away the old IC fittings.

The remaining “feet” were removed with a soldering iron. Once done, I just popped in the new 28-pin IC fittings and soldered them in place.

New fittings for the EPROMs and RAMs in place

All done.

Now I started measuring the connections on the new fittings and found that more than half were bad. This is going to be a lot of work. I’ve started wiring on the back side of the PCB, but time ran out, so I’m not finished yet. I have to redo connections between both RAM fittings and between the left RAM and right EPROM fittings. There was clearly a lot of damage from the battery leakage.

First two connections repaired, many to go…

I will keep you updated on my progress.