Zenith Z90

This was quite a find. Here's what I did to get it going: First I fixed the dry joints on the power supply board. This bought the monitor back to life. Nothing else needed to be soldered. CP/M booted but it complained about a read only file. This was the submit temporary file, which was somehow set to read only. I assembled a small program to change the file attributes of the file, then entered that into memory with the boot monitor. It was about 20 bytes. When I got a prompt, it would crash after pressing enter. I printed the CP/M source listing and started tracing through it. After a bit I noticed 256 bytes (one physical sector) worth of data was completely wrong on the third sector into CP/M, starting at D200h. CP/M itself starts at D000h. There wasn't much else I could do except enter the whole 256 bytes in manually with the boot monitor. I knew there was a problem however, because should I warm boot CP/M for any reason, it would overwrite the code I entered in memory. I made a backup copy of that data in memory just below CP/M in case that happened. It was just a short bit of code using the LDIR Z80 instruction. I was incredibly fortunate to find a disk sector editor on the A: partition of the hard drive, so I ran it and modified the faulty sector again manually, entering another 256 bytes. So now it's working. The system has a 2.048MHz Z80, 64kB RAM, 3-port serial card, a soft sector floppy controller, a 96 TPI floppy drive and a 10MB hard drive and associated bus interface. The system came with manuals for the internal cards, CP/M and Microsoft BASIC. I don't have the top cover on it because the fan is clogged up and won't spin. It's a 115VAC fan running off the transformer. The whole thing stunk of WD40 when I opened it...