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IBM PC XT Smoking whilst switched off!?

I

IBM Portable PC

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Jan 15, 2008
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Location
70 Miles NW of Melbourne, Australia
I heard a crackle or two today from an unknown source and finally a more significant crackle and telltale smoke. No surprises here with virtual computers, however I have not had one do this before when it has been switched off for over a month!

The power lead is live, however the red switch is definately fully in the off position.

There are also at least 2 surge suppressors on the power and an online UPS after those.

I don't have time to look now, I've pull the power lead out, and assume there must be an input filter capacitor or two that have finally given up after 30 years.

Any other suggestions?

A faulty power switch perhaps, although the cooling fan was not running.
 
So, noise/smoke when mains (house) power was applied to the PSU, but red switch on PSU was in the off position.

If your PSU matches the particular one shown (here) in the Sams Computerfacts for the IBM 5160, then there are components before the power switch. One of those components is a suppression capacitor. My money's on that.
 
modem7 said:
So, noise/smoke when mains (house) power was applied to the PSU, but red switch on PSU was in the off position.

If your PSU matches the particular one shown (here) in the Sams Computerfacts for the IBM 5160, then there are components before the power switch. One of those components is a suppression capacitor. My money's on that.
Click to expand...

I concur, either that or perhaps I need some holy water, rosemary beads and a priest... :eek:
 
Probably that RIFA cap across the line. Remember to only replace with a cap with a safety rating for going across the AC line. Or leave it out.
 
I have to imagine these failures are more likely to happen in 230 VAC countries. One of the downsides of being able to boil a kettle of water faster...
 
I had that happen to me once a long time ago after i'd gone to bed, I got woken up by the smoke alarm, I'd been using the machine and shut it down but forgot to switch off at the wall socket, Bloody crappy old RIFA caps, None of my machines have rifa caps in now, The ones that had RIFA's have all been replaced with better 300V + X2 rated caps.
 
Well, our power is based on UK 240VAC infrastructure, but manages to stay within tolerance of the newer 230V standard. My local mains sit around 235V.

From wiki:
Most of Europe, Africa, Asia, Australia, New Zealand and most of South America use a supply that is within 6% of 230 V. In the UK and Australia the nominal supply voltage is 230 V +10%/−6% to accommodate the fact that most supplies are in fact still 240 V
Click to expand...
 
I just measured at the wall socket 9:50PM and got 248 VAC this is around the norm for where i live now, It can go higher at times 255 - 260
 
Yes, we learned that lesson in the 1980s when the PCB manufacturing equipment my US employer sold would have problems in the UK market because we designed it for a nominal 230, but on-site would see those sorts of peak voltages.

Somewhere I saw a documentary on the UK power system where they would watch the line frequency for droops (due to load) as commercial breaks approached in TV prime time when everyone switches on the electric kettle. They would bring in power from across the channel to meet demand.
 
paul said:
Somewhere I saw a documentary on the UK power system where they would watch the line frequency for droops (due to load) as commercial breaks approached in TV prime time when everyone switches on the electric kettle. They would bring in power from across the channel to meet demand.
Click to expand...

You can monitor the UK power frequency real-time here:

http://www.dynamicdemand.co.uk/grid.htm
 
Well, using that analogy, leaving an XT plugged into a wall outlet while switched off is like smoking in bed, it could burn the house down while you sleep :)
 
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