Troubleshooting an IBM 5155 - (portable personal computer)

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Jan 17 17:41:56 2005

> > b) There is no useful signal from the side-1 head (this is the head on
> > the top surface of the disk, of course),
>
> For all the possibilities you state, likely cause.

Sure, _IF_ that would cause the MS-DOS format program to assume the disk
is single-sided.

>
>
> > Well, although _now_ I have some very nice test gear, I debugged my first
> > homebrew computer (This was when homebrewing meant soldering chips to
> > stripboard and wiring everything up, not pluging a video card into a
> > motherboard) with an anlaogue multimeter and an LED+resitor 'logic
> > probe'. So it certainly _can_ be done...
>
> Likewise! On my very first own computer, SWTPC 6800, I debugged
> the fact I miswired the (20mA loop) tty using a Tek 555 scope to

Yo uhad a 555? I managed (then) without a 'scope at all. Now my 555 is
alongside me with a good selection of plug-ins. I don't use it all that
much -- I find a logic analyser to be a more useful instrument, but anyway.

> ID the Mikbug code loop waiting for the start bit. I was too dumb
> to realize I should have checked for Rx into the PIA :-)
>
> Soldered every damn chip and all those molex "card edge"
> connectors one at a time. Ugh. Plus a whole tube of 2102's (and
> not 21L02's) a year later.
>
> Now I buy only laptops, nearly impossible to even open them, and

Yuck! I'd not want a computer I couldn't easily pull apart, and I'd not
want one without proper expansion (not Useless Serial Botch). Heck, I've
even played about with the processor bus in HP handheld calculators...

> quite happy with that. :-) Even having to stick in a PCMCIA card
> these days seems invasive. Why isn't that built in?
>

The stuff I want is rarely built in, because no sane person would want it...

-tony
Received on Mon Jan 17 2005 - 17:41:56 GMT