Computer repair due to incorrect voltage set

Hello,

I'm debating whether or not to try and fix a computer that was turned on and run for some period of time with the incorrect voltage set on the power supply (220V instead of 110V.) I'm guessing that incorrectly setting the input power on the supply causes a more or less standard effect on the computer, most likely mother board power regulation - anyone know what this effect is? Any help is greatly appreciated! I don't want to go down this path just to find out every part on the board is toast!

Thanks!

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News
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I don't think it would do any damage. I imagine the designer of the P.S. took into account the possibility that this might happen. Especially if you had it set for 220v and plugged into 110v.

Reply to
LB

and

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The computer is probably just fine, though I'd be inclined to replace the damaged power supply rather than try to repair it, though it could be something simple like a blown fuse.

Reply to
James Sweet

I'm surprised that this hurt anything. If you plugged it into 110, but set the switch to 220, then the power supply was seeing only half of the primary (i.e., input) voltage it was expecting. Because of this, it was probably unable to produce the proper secondary voltages (5VDC, 12 VDC, etc) since the regulators ran out of headroom. But I wouldn't expect this to damage anything in the power supply. And I can't think of anything on the motherboard that would be hurt, either. I'm not as sure about the display's deflection circuitry, assuming you have a CRT monitor - but the display isn't powered through this switch.

With the switch correctly set, can you measure the power supply secondary voltages?

Interesting question. Please let us know what you find.

Bill =======================

News wrote:

Reply to
Bill Jeffrey

I tend to agree. here in Australia we run on 240 volts. Setting a power supply on 110 volts would produce a short sharp , and the power supply would be stuffed, however, in the reverse situation, I cannot see off hand why inputting half the voltage for which it was set would damage it. I suppose with modern power supplies there could be other factors where even that scenario would produce a failure.

Henry.

Reply to
hemyd

"hemyd" wrote in news:426acf2c$0$4658$ snipped-for-privacy@news.optusnet.com.au:

IMO,at half nominal input voltage,the switcher would not start. Should not,if properly designed.

At 2X input V,yes,the switcher transistors would blow quickly...then the fuse. 8-)

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Jim Yanik
jyanik
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Reply to
Jim Yanik

Some power supplies will self destruct with too low an input voltage. The duty cycle pegs and the transformer saturates.

Reply to
James Sweet

The

First part I agree. Second part here is the issue:

It doesn't make the transformer saturate, to do so will present a too high output. The amount of FIELD in it determines the output and that does not increase, except when a bad fault exists in the regulation loop or in some cases tuning. If the snubber network opens up, or part of the Xformer core pulverizes or cracks it might well cause this unless there is a working shutdown circuit. If destruction is not immediate, it is because the chopper is running at too high a frequency to bring it into regulation, at least with most SMPSes.

The problem with low voltage is twofold. One it usually causes the chopper to run at a lower frequency. This may cause the collector or drain current to go beyond it's peak rating. (Ic peak). It is still charging the magnetic field to the same level if it is in regulation.

Two, the drive optimization circuit is outside of design limits, which means in the case of a bipolar chopper it may run out of base current and overheat. The same is true of drive voltage for a FET chopper. Even though the input impedance of the FET is high, the driver usually slams against some diodes and this can cause exactly the same thing, although this particular failure mode would be more apt to happen with a bipolar chopper.

Actually I'm surprised that the OC protection didn't keep it from booting, it must be very lightly loaded. When the OC protect is on the hot side it is usually a resistor on the source or emitter of the chopper, and even at the same output THAT current would increase, actually double, almost exactly double. Of course then there are only about =BD the number of spikes, so some OC protection circuits might not catch it.

I do agree with you, but I don't think that such a power supply can actually get past a certain duty cycle.

[Hot damn, I just thought of something. Since we're talking theory a bit here. I think I might know a good reason that Sony doesn't have a DC fuse after their SMPS.

To take Devil's advocate, if they put a fuse on it, when the HOT shorts the time waiting for the fuse to blow would result in a tremendous spike, possibly destroying all the other electronics in the set. They could filter it after the fuse but if that filter went bad it would be an insidious fault. Remember what happens when the 503Khz crytal stops while the countdown has the HOT turned on. Those are fun to run down because you get no indication of what happened.

This of course offers them no reprieve from the fact that they didn't put any current limiting in it. This is technology they had in the early 80's. These things are higher tech ? That's like touting a supercharger on a car and putting crappier brakes on it.

I already own all the Sony product I ever intend to, unless I get gifts.]

Anyway, in a nutshell, the computer PS runs out of drive current or voltage for the chopper I think, while I know that alot of the driver chips can do a 100% duty cycle, I think you'll find the feedback amps designed to prevent this, but they probably let the duty cycle go higher than it really should. This is to prevent a brownout from causing a restart, but that is supposed to be temporary. The OP had a permanent brownout situation. IMO, even with good fans it probably overheated due to Dv/Dt. Just like an HOT with insufficient drive.

JURB

Reply to
ZZactly

Just replace the power supply and be done with it. It does not sound as if you would be willing of replacing the blown electrolytics and possibly diodes inside of the supply.

--
Met vriendelijke groet,

   Maarten Bakker.
Reply to
maarten

Correction: blown switching transistor, I falsely assumed you ran a supply set for 115V on a 230V outlet.

--
Met vriendelijke groet,

   Maarten Bakker.
Reply to
maarten

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