In addition to my working Apple //c and //e I have two Apple //c’s that don’t work well.
The first is my original Apple //c that I bought in 1984. The other //c was one I bought on eBay. The rear corner of the case was broken in shipping. The seller replaced it with what is now my working Apple //c.
My working //c is a ROM 3 and the two non working Apple //cs are ROM 255. I want to repair them, if possible. I have narrowed down the initial problems to something with the RAM.
Apple released several versions of the //c, with different ROMs. The original ROM is 255, also the smallest. The next version is ROM 0 which added support for the 3 1/2″ diskette drives and a self test of the //c. Later versions 3 and 4 are for memory expansion.
In order to assist with fixing them, I ordered a new version of ROM 0 for one of the machines. It came with very good instructions, but in a abundance of caution, I still resorted to YouTube to watch videos of the upgrade. Specifically, opening the case and the actual ROM upgrade.
The motherboard of the Apple //c ROM 255 is designed to be upgradable to the bigger ROMs. You need to a cut a trace on the motherboard and put a drop of solder between two pads to make a jumper. Once that is done you just switch out the old ROM 255 with the new ROM 0.
That sounds easy, right? The big draw back for me was the whole soldering thing. I learned a few basics about soldering in high school, I believe the year was 1978. That was also the last time I tried it.
I did a quick test of both machines to see what I had to work with. My original //c didn’t even try to boot the diskette drive, which was odd because I remember it working the last time I tried it. The other one attempted to boot, but just grinded away with out stopping. I decided to go with my original machine.
I opened it up and found the ribbon cable on the internal drive was loose. I tightened it up and went on with my upgrade. I cut the trace and fired up my new soldering iron and managed to get a drop in the right place. After swapping the ROM I put it all together again and fired up the Apple //c and ran the self test.
RAM 00100000
was the message returned by the self test. That tells me one of the ram chips may be faulty which will be another project. The disk drive appears to be alright after tightening up the cable.
Since this ROM upgrade showed positive results, I ordered and received another of the ROMs for the other //c.
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