TRS-80 Fireworks

Peter Coghlan cctalk at
Wed Aug 28 04:05:39 CDT 2019

Matt wrote:
> On 28/08/2019 09:15, Marvin Johnston via cctalk wrote:
> > I'm just curious how many people have powered up their TRS-80
> > computers, and ended up with a bang and a room filled with smoke?
> >
> > So far, I've gotten the fireworks in two out of two TRS-80s (model 3
> > and 4) when they were powered up. In both cases, the problem was with
> > the main line filter capacitor mounted on one of the power supplies.
> > The computers continued to work which was my first clue the problem
> > was not serious :).
> >
> > Is this a normal problem with these older computers? I'm used to
> > seeing the electrolytics give problems, but this is the first time
> > I've seen one of the X type line filter caps blow.
> This is very common for these paper line filters. I've had the same
> failure with an Osborne 1, DECserver 200, DELNI and PDP-11/73. There are
> many more devices that have them; generally anything with an Astec brand
> power supply. I replace them before even powering up these days.

I've had several instances of it with BBC Micros, also containing Astec brand
power supplies.  Typically, when switched on after a long period of idleness,
the machine works fine for minutes to hours, then there is a quiet pop followed
by a whoosing noise and smoke starts pouring of the mains filter capacitor
while the machine continues to work away quite happily.

Peter Coghlan.

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