14 Oct
2005
14 Oct
'05
12:17 p.m.
I did get this last Sunday - about 5 large boxes of
manuals, binders,
floppies and tapes, plus the computers. I did find time to fire up
the Model III, unfortunately, it seems to have a problem - no text on
power-on, and no indication of anything running except for the usual
drive 0 spin up and access light for about 2 seconds. The screen has
power - you see a white flash and squiggle on power off (usual mono
CRT shutdown kind of flash and squiggle), but never any text or
fragments of text. Pressing the reset button does get a power-on-type
reaction from drive zero, but that's it.
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.
It's been about 22 years since I used a Model III, so my memory is a
little faded about it. Are there any ROM-based diagnostics? Anything
ever get spit out of the serial port? I wish I had a Z-80 pod for my
Fluke 9010A (have 68000 and 6502) - it's a great way to sleuth around
inert micros.
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!), you can then tip the cover
on to the left hand side and put it alongside the base part of the
computer and leave all the cables connected. The machine will run like that.
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.
Any and all suggestions (including schematics) are welcome, especially
if anyone knows of a site remotely resembling funet, but for TRS-80
stuff.
I am pretty ssure I found a site with TRS-80 service manuals, etc.
Something like www.trs80.org, or www.trs80.com...
-tony