In part one I took a look at this PC XT clone, and it came in with several known problems from the first round of testing, including bad RAM, a leaking clock battery, and an MFM hard drive full of errors. I went ahead and started with the memory since replacement chips had arrived. By swapping chips within the second bank and checking the BIOS each time, I found two bad RAM chips, replaced them, and got the machine back to the full 640K.
With the memory sorted out, I put the original BIOS chip back in just to see what would happen. This time it booted normally without changing any jumpers, so the earlier 128K behavior turned out to be a quirk of the BIOS reporting rather than the actual installed memory. From there I turned to the multi-I/O card, which handled the floppy controller, serial and parallel ports, game port, and real-time clock.
The onboard battery had already started leaking, so I removed it and cleaned the area with vinegar and IPA. Once the nearby sockets were out of the way, I found corrosion damage around the battery pads and traced the affected runs on the two-layer board. In the end only one trace was actually open, right near a pad by the clock chip, so I repaired that and reinstalled the clock socket. For the replacement battery I fitted a CR2032 holder and added a diode on the positive side so the coin cell wouldn’t be charged by the circuit.
I tested the card carefully before going any further. The floppy controller still worked, which was the main concern, and the clock utilities for that RTC chip let me set and read back the date and time properly. The clock didn’t update DOS automatically on its own, so I added the getclock command to AUTOEXEC.BAT so the system would pull the saved time at boot.
The hard drive took much longer. SpinRite 5 only made it about halfway through before hanging with no more disk activity, so I switched to SpinRite 2 on Adrian Black’s recommendation. That run took about 36 hours, but it completed and low-level formatted the bad areas. After that I deleted the old partition, created a new DOS partition, formatted the drive, and ended up with roughly the full 20MB available again. A follow-up surface scan showed the tracks as usable.
Once the drive was stable, I installed MS-DOS 5.0 from reproduction floppies I had made. Setup completed normally, the machine booted from the hard disk, and I copied over a few utilities and games for testing. CheckIt identified the system as running at PC/XT speeds with EGA video, which matched what this clone was supposed to be.
The case cleanup made a big difference too. Soap and water removed a lot of the grime, and lighter fluid worked best on the black scuff marks and old foam tape residue without damaging the paint. I used a magic eraser sparingly on the stubborn spots, cleaned up the plastic front separately, and finished it off with a new custom badge.
In the end the XT clone was back up and running with 640K, a working RTC battery mod, a usable hard drive, MS-DOS 5.0, and enough stability to run a few games like Arkanoid and Alley Cat.
— Aaron
Links
Timestamps
00:00 – Intro and recap
01:26 – Fixing the memory
02:38 – Fixing the clock battery
12:09 – Testing the clock
16:11 – Fixing the hard drive
18:52 – Installing MSDOS 5.0
24:05 – Cleaning the case
31:21 – Testing and games
38:27 – Wrap Up