Radio Shack TRS-80 Models I and III available near NE Ohio

[Ethan Dicks]

On 10/15/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> Have yopu tired powering up (or pressing reset) while holding down the
> Break key? A Model 1/3/4 fitted with a disk controller will normally try
> to boot from drive 0, but if you hold down Break, it'll go into ROM
> BASIC. You should get a CASS? prompt (hit enter), then MEMORY SIZE (enter
> again), then get the BASIC sign-on.

I did not try that - I knew there was some reset/key combo but had
forgotten what key to hit.  But I'll try that as soon as I'm in front
of the machine again (I'm not home right now).

> The Mofrl 3 is actually quite easy to work on. If you pull the cover, the
> monitor section comes off with the cover (be careful not to break the CRT
> neck when removing or refitting that cover!),

Heh... I've worked on Classic Macs... had that lesson already.  :-(

> The CPU board stabds vertically at the back, possibnly covered withe a
> metal shield. Remove that, and you're looking at the component side of
> the PCB. The model 3 is mostly TTL, with some RAM (4116 DRAMs, 2114 SRAMs
> for the video), ROMs, and a Z80.

Right... I did find GIF schematics and pored over them last night.  I
remembered correctly that there's not anything truely bizarre going on
in there - worst case, I can trace faults down to individual chips,
then as part of the replacement process, remove them intact and test
them in an external hand-held IC tester for final confirmation of the
fault.  It's easier to clip leads and extract single pins, but I am
good at removing chips without damage.

-ethan