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!

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.




On Sat, 23 Apr 2005 14:32:30 -0400, "News" wrote:

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!

"News" wrote in message
...
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!



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.

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:

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!

"Bill Jeffrey" wrote in message
news:1Uxae.64116$A31.36134@fed1read03...
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
=======================

I tend to agree. here in Australia we run on 240 volts. Setting a power
supply on 110 volts would produce a short sharp bang, 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.

"hemyd" wrote in
:

"Bill Jeffrey" wrote in message
news:1Uxae.64116$A31.36134@fed1read03...
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
=======================

I tend to agree. here in Australia we run on 240 volts. Setting a
power supply on 110 volts would produce a short sharp bang, 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.




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-)

--
Jim Yanik
jyanik
at
kua.net

"Bill Jeffrey" wrote in message
news:1Uxae.64116$A31.36134@fed1read03...
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.


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

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

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

News wrote:
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!

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.