Tryout and teardown of two Tandy Colour Computer 2s

[intabits]

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...

[W0MJ]

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

[W0MJ]

Uniboard pictures

[W0MJ]

... 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).

[ozcar]

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!

[W0MJ]

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 0001
2 - ON (serial I/O console) % 0000 0010
3 - OFF (not read in monitor ROM)  %0000 0100
4 - 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 EF40

Next:  boot a Flex diskette!

[W0MJ]

Any progress on the Uniboard?
I have a working computer, can possibly help… if so, let me know.
-Matt W0MJ

[intabits]

Any progress on the Uniboard?
I have a working computer, can possibly help… if so, let me know.
-Matt W0MJ

(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.

[W0MJ]

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. W0MJ
w0mj@arrl.net