[Coco] (Marginally Topical) TRS-80 Model I Troubleshooting

[Gene Heskett]

On Monday 05 August 2013 18:22:46 Joel Ewy did opine:

> On 08/05/2013 08:26 AM, Andrew wrote:
> > Joel,
> > 
> > You've probably thought of this, but my first thought on the "touchy
> > v-hold" was to squirt some cleaner on the pot. May or may not be that
> > simple, of course (indeed, what you mean by "touchy" is probably
> > influencing my suggestion).
> 
> Thanks Andrew.  I actually hadn't thought about the pot yet, but I don't
> really think that's the problem.  I can get it to hold if I adjust the
> pot just right and don't breathe on it.  And it does seem to lock into
> place, but the hold feels weak, if that makes any sense.  I would think
> a dirty pot would seem to jump around in value more as I turn it.  In
> this case, it seems more like the 'hold' just has a weak grip.
> 
If its a transistorized circuit, as opposed to tubes, the "Capacitor 
Wizard", walking around in it and checking the electrolytic capacitors will 
probably be the most enlightening thing you can do.  Old caps dry out and 
develop high resistance internal connections.  The teeny little ones with 
25 volt and below voltage ratings are infamous for that when running in a 5 
volt digital logic circuit.  Its an amazing little meter, with a gold 
plated price tag, but in a service shop, it will save you its nearly $200 
price tag just in the time to find bad caps the first week you own it.

The same comment could be applied to old tube circuits, but they generally 
run on higher voltages which tend to keep the caps better "formed" and 
working for longer periods of time.  Then they die at about the same rate 
as the tubes do, usually from the tubes generated heat.
  
> > As for the other stuff, I can't really help you there; have you been
> > able to find any general TRS-80 lists (or specific to the Model I)?
> > I'm sure something exists, it was a very popular early model. There's
> > always the vintage computing lists. Also, be sure to check Reddit:
> > 
> > http://www.reddit.com/r/vintagecomputing
> > http://www.reddit.com/r/retrobattlestations
> 
> Yeah, I'll try the Vintage Computing list if I can't figure it out
> otherwise.  But I know there are people on this list who have had
> experience with the Model I.  Thanks.
> 
> JCE
> 
> 
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Cheers, Gene
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