I’ve continued work on my KC/CUTS tape decoder program. The decoder works well with clean audio files, but not so well with noisy ones. I’m not completely convinced that using the Goertzel algorithm has been a good idea; possibly just using FIR filters would have been more suitable. Also, rather than using fixed filter frequencies, it might be a good idea to do some carrier tracking to account for tape speed variation, possibly using a DPLL.
I’ve taken various photos of four Sol-20s in various stages of disassembly. One of them has some nice labels from Micromation on the top backplane connector giving designations of all of the S-100 signals. Another has two daughtercards from Micro Complex, one adding a 80×24 video mode, and one replacing the standard 8080 microprocessor with a Z80. That machine also has the Micro Complex dual personality module, and probably has the modification to allow relocating the ROM, video RAM, and scratch RAM from Cxxx to Fxxx.
One of the Sol-20s came with a Compupro RAM 17 64KB static CMOS RAM card. I put it in the Sol-20 with the S-100 labels. The video seems to be unstable for the first ten seconds of operation, but settles down. It seems to basically work OK. The only NTSC monitor I had at hand was a Sony KV-1380 Trinitron color TV. It works, but the monochrome bandwidth isn’t really satisfactory for 64-column text. I’ll have to dig a monochrome monitor out of storage.
Naturally the foam disks in all four capacitive keyboards have gone bad. Each keyboard has a few keys that work OK, a few that work sometimes, and many that don’t work at all. Only one had enough keys working to check that the Solos firmware works.
The newer two keyboards use Phillips screws, which are easily removed. The older two use a strange screw head I’ve never seen before, which is like a slotted, but with a round hole in the middle. The slot is too narrow for any of my normal screwdrivers. Jeweler’s screwdrivers will fit the slot, but are not wide enough to stay in the slot, rather than slipping into the hole in the middle. I managed to remove 6 of 18 screws from one keyboard before giving up.
Tomorrow I’ll put the new foam disks into one of the keyboards.