| bh | Microtel Engineer's Portable Unit Log |
| Manufacturer: | Private project of a group of Microtel engineers |
| Model: | Portable using a Xerox-820 mainboard |
| Serial Number: | - |
|
Logic board: IC date codes early-mid 1981
Disk drive: IC date codes 80nn, DIP switches 8235 Power supply: latest IC date code 8147 | |
| Date of Receipt: | ~ 2003 |
| Source: | NS |
| State upon Receipt: | Excellent physical condition. Second 820 mainboard included. |
| Date: | 2009 Dec |
| Symptoms: | Powered up, screen filled with @ and P except at beginning where monitor message is displayed, which is likewise scrambled. Would appear to be video-memory problems. |
| Analysis: | Second 820 board swapped in to check it, display good, monitor comes up "XEROX 820 VER. 2.0". |
| Solution: | Two 9114's for high-order-bits of video memory on first board replaced with TMS2114-45NL, sockets installed. Video problem fixed: reset/power-up brings up monitor "XEROX 820 VER. 2.0". "a" command with boot disk boots to "Big Board CP/M 60K VERSION 2.2.1". |
| Date: | 2013 Feb |
| Symptoms: | Powered up. Some keys not functional, correlates to keyboard data bit 0. |
| Solution: | Keyboard opened and connector exercised, OK, now functional, may have been connector pin cleaned by insertions. Now boots to CP/M, DIR works, some other commands hang. |
| Date: | ~ 2013 |
| Procedure: | Transferred to RF. |
| Date: | 2021 |
| Procedure: | Transferred to UVic. |
| Date: | 2022 Jul |
| Symptoms: | Some keys again not functional, appears to be same problem of 2013 Feb. |
| Analysis: |
Again, OK after keyboard has been opened.
Signal levels observed on data lines from keyboard onto main board:
appear OK, nothing unusual or distinguishing.
Problem appears again a few days later. Signal for LSB bit now middling at Z5.1,2 input: 2V L ~ 3V H. Connection through IC socket at Z12.2 (output from keyboard scanner) poor, varying up to > 60 ohms. |
| Solution: | Z12 reseated, OK. Socket is SCANBE, side-contact pins. |
|
Unit Log
MEP |
bhilpert 2022 Jul |