Xerox 820-II, ca. 1982 | |
CPU: | Z80A @ 4MHz |
RAM: | 64KB |
Floppy Drives: | 2 Shugart SA800 8" single-sided drives |
Display: | 12" White (24x80) |
Ports: | 2 RS-232, parallel printer (internal), floppy/hard drive |
Model: | 820-II |
Serial No.: | |
OS: | CP/M 2.2 |
ROM: | 6KB (monitor and ROSR)) |
Original Price: | $3,295 |
Notes: |
When I received this system, the previous owner pointed out an X-class filter capacitor in the power supply which had exploded when he turned it on. I replaced that cap, along with 3 other X- and Y-class caps for good measure. After that, the unit powered up and displayed the monitor prompt, but the keyboard was mostly non-functional: extra characters, incorrect characters, and at least 2/3 of the keys didn't work at all. I tracked that down to a defective CD4051BE 8-channel analog multiplexer chip on the keyboard PCB. After I replaced the 4051, the keyboard worked, but the system would not boot from diskette. I eventually found the cause to be a defective 4164-20 RAM chip (U7) which had a bit stuck on zero from ED80 - EDFF. After the RAM chip was replaced, the system booted normally from diskette. |