[time-nuts] HP 5328 PSU nightmare...

Dave Baxter dave at uk-ar.co.uk
Thu Sep 10 08:46:00 UTC 2009

You could try replacing the fuse temporarily with a "suitably rated"
filament lamp.

You'll need to figure out what volts/power etc, from what the fuse is
protecting, and the fuse's rating.

But, if done (and it's not too difficult) you end up with a self
indicating current limit!   (Of course, you could design and fit an
"Electronic" fuse...)

When you've found and removed the overload, often the device/instrument
will start to work (maybe not very well) with the bulb still in there,
but said bulb will not glow as bright, if at all.

Filament lamps have the nice PTC feature, that when cold they have a
lower resistance than when hot, so for no fault conditions, things can
actually work quite well.  When the fault happens, the lamp lights,
"Indicating" the problem, but not letting too much current flow to cause
more damage.

It's a simple trick, but one I've used on many an occasion, from 12V
vehicle electrics, right up to 240V AC House electrics with a 60W lamp!
(Unscrambling a nightmare caused by a so called "Professional"
electrician, who walked away from the job, leaving multiple shorts in
the lighting circuit.)

I make no claim for originality, as I learnt the trick when working for
BT (the Telephone co in the UK) years ago, but it's stood me in good
stead on many occasions with various "Barsteward" electrical woes...

I even used to have an old television of my own (I was given it!) where
I ended up with a 24V bulb in series with the DC feed to the line output
driver transistor, because that used to "Pop" on odd occasions.  I never
found out why (neither did the TV repair guy, which is why I ended up
with it I guess) but for some years (until I donated the TV to a local
hospice) if you turned it on and got no picture, just cycle the power
and it'd come up OK the next time, not needing any surgery!   That used
to happen on average about once every week or two from memory.


Dave B.

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