Tryout and teardown of two Tandy Colour Computer 2s - Page 1
Forum section: electronics / general

author: intabits
author_rank: Frequent Contributor
timestamp: March 29, 2020, 10:10:12 pm
content: To help with repairing my Compacta Uniboard, I was looking for a working 6809 based system to help develop a ROM emulator gizmo using a RAM chip.I have an old Tandy Colour Computer 2, that I tried to fire up after 35 years of storage:-No joy there, so I bought another CoCo to satisfy my original aim, and also to help with fixing the first CoCo:-At least that one works.Now to play with RAMs, ROMs and CoCos...

author: W0MJ
author_rank: Contributor
timestamp: May 12, 2020, 01:06:33 pm
content: Posting a picture is hanging-up my post; so i will 'just post' then try the picture.I have seen the "?_" prompt, but only occassionally, and only if i have DIP switch 2 set to 'off' (monitor and keyboard versus serial I/O).i cleaned the pins of all chips except the RAM 932 of them!) and it came up, reset a few times, and looked good; i do not have a keyboard wired correctly, so i could go no further. I tried to chagne the DIP switch to serial I/O, and got the RAM dump screen. dang.I will try to post a picture....Thanks!-Matt

author: W0MJ
author_rank: Contributor
timestamp: May 12, 2020, 01:10:11 pm
content: Uniboard pictures

author: W0MJ
author_rank: Contributor
timestamp: May 12, 2020, 01:20:48 pm
content: ... that should be (32 of them), i.e. the count of RAM chips; the shift did not shift and i ended up this a lot more memory! <grin>The keyboard i have is from a broken (non-repairable) piece of test equipment, a Nicolet analyzer - it had literally fallen off a truck, but the keyboard is intact. The encoder chip is an OKI part, MSM3914-34RS - any info on that one? i can kinda guess as to the data and strobe lines, and maybe the power; but i would hate to be wrong.Any help appreciated. I found an OKI data book but it only has processors.Once i get the keyboard 'correct', i can try to go further, if and when i get the prompt again (like memory test).

author: ozcar
author_rank: Frequent Contributor
timestamp: May 14, 2020, 05:21:42 am
content: Reading this prompted me to dig out an eprom programmer I made "only" around thirty years ago, using a 6809. The challenge was finding the somewhat strange serial cable I used for the thing, but I found it still works!

author: W0MJ
author_rank: Contributor
timestamp: May 14, 2020, 12:53:59 pm
content: The Compacta Uniboard 6809 is now running, reliably. Memory test ran over-night with no errors; line of '!!!!!!!!!!!!!!!!!!! ...'i have not gotten the parallel keyboard wired, but it should not be too bad; i know where +5 and ground are on the board, and i can put a 'scope probe on outputs to find the strobe and data lines.Issues were related to the DIP switch (bad contact, could not use a SIO console!), and (mostly) the IC sockets for U32 and U40. the pins were bent funny, so i used a dental pick to re-form them... they should be replaced with machined sockets!All ICs were removed and pins cleaned (pencil eraser, DeOxIt).All solder connections checked with a magnifying light, all 'looked okay'.DIP switch settings: (memory location EF4B, also called 'P1' in monitor; look for START1 F018)1 - ON (boot from 5.25" diskette) %0000 00012 - ON (serial I/O console) % 0000 00103 - OFF (not read in monitor ROM) %0000 01004 - OFF (ON = /RESET) , same as P5 (pin-1 = Grd, P-2 /RST)P7 - RxD jumper 2 - 3 for RS232C (vs 1 - 2 for 20mA current loop)terminal: 8 - N - 1 1200 bps (location F093 - F09A - ACIA control register set to $18 (see 6551 data sheet) - look for ACIBAS EF40Next: boot a Flex diskette!

author: W0MJ
author_rank: Contributor
timestamp: January 12, 2025, 01:36:00 am
content: Any progress on the Uniboard?I have a working computer, can possibly help… if so, let me know.-Matt W0MJ

author: intabits
author_rank: Frequent Contributor
timestamp: February 20, 2025, 02:20:24 pm
content: Quote from: W0MJ on January 12, 2025, 01:36:00 am(just saw your post)No, haven't touched it for a long time. It's on the list...Another approach that I'm interested in trying is to remove the 6809 and use an arduino (one with lots of I/Os) to drive the board from the CPU socket. I should then be able to unit test each subsection fairly easily, without needing almost the whole thing to work to debug it.

author: W0MJ
author_rank: Contributor
timestamp: October 16, 2025, 12:57:41 am
content: Moving, downsizing.Compacta Uniboard 6809 and all docs, diskettes for sale. Parts could get heavy so probably not sensible to ship monitor; works with RS-232 terminal.PM me for details.Thanks.Matt. W0MJw0mj@arrl.net