computer power supplies..

[larya]

Is there a group for repairing computer power supplies?..
Question... I have the power supply out of the computer...
Besides pluging it in... how do you turn it 'on'...
The front panel on / off switch connects to the mother board..
How can I turn the power supply 'on' at the power supply?...
Larry

 

[Michael Karcher]

How can I turn the power supply 'on' at the power supply?...

If it's ATX, ground the PS_ON pin.

See Wikipedia for Pinout.

Regards,
Michael Karcher

 

[PlainBill]

Is there a group for repairing computer power supplies?..
Question... I have the power supply out of the computer...
Besides pluging it in... how do you turn it 'on'...
The front panel on / off switch connects to the mother board..
How can I turn the power supply 'on' at the power supply?...
Larry

Not a group per se, but the BadCaps forum -
http://www.badcaps.net/forum/index.php? - has a section on computer
power supplies. A large part of the discussion is about the
deficiencies of various vendors. One vendor actually glues iron
weights inside their power supplies so they weigh more. A heavy power
supply must be better, right?

Fry's Electronics sells an inexpensive 'test box' for power supplies,
but it is very limited.

PlainBill

 

[westom]

Is there a group for repairing computer power supplies?..
Question...  I have thepower supplyout of the computer...

Do you have and use an oscilloscope? Good, now you are ready to
start learning this stuff. Take lessons on transistors, pulse width
modulation, diodes, filters, .... You will not believe how many
functions are required in a power supply if you did not read its full
page of numeric specs. To fix a power supply means you understand
what those specs say. Implied - how many self proclaimed computer
'experts' do not even know what a power supply does. They think it
only provided voltage. Learn how complex a power supply really is and
the many functions it performs.

Of course, learn of the power supply controller – another component
that many do not even know exists.

 

[Eeyore]

Do you have and use an oscilloscope? Good, now you are ready to
start learning this stuff. Take lessons on transistors, pulse width
modulation, diodes, filters, .... You will not believe how many
functions are required in a power supply if you did not read its full
page of numeric specs. To fix a power supply means you understand
what those specs say. Implied - how many self proclaimed computer
'experts' do not even know what a power supply does. They think it
only provided voltage. Learn how complex a power supply really is and
the many functions it performs.

Of course, learn of the power supply controller – another component
that many do not even know exists.

And be damn careful with the voltages inside.

Graham

 

[Eeyore]

Not a group per se, but the BadCaps forum -
http://www.badcaps.net/forum/index.php? - has a section on computer
power supplies. A large part of the discussion is about the
deficiencies of various vendors. One vendor actually glues iron
weights inside their power supplies so they weigh more. A heavy power
supply must be better, right?

I fixed an ATX supply by replacing 2 very obviously bulged caps on the
output side with ones from a scrap Mobo !

Graham

 

[Eeyore]

If it's ATX, ground the PS_ON pin.

See Wikipedia for Pinout.

Beware. It may not regulate properly with no load on the 5 or 12 V
output.

Graham

 

[john]

Is there a group for repairing computer power supplies?..
Question... I have the power supply out of the computer...
Besides pluging it in... how do you turn it 'on'...
The front panel on / off switch connects to the mother board..
How can I turn the power supply 'on' at the power supply?...
Larry

just fixed mine yesterday
replaceing the low imp caps on the
outputs.

 

[ZACK`]

Is there a group for repairing computer power supplies?..
Question... I have the power supply out of the computer...
Besides pluging it in... how do you turn it 'on'...
The front panel on / off switch connects to the mother board..
How can I turn the power supply 'on' at the power supply?...
Larry

just fixed mine yesterday
replaceing the low imp caps on the
outputs.

 

[bob]

http://www.informit.com/articles/article.aspx?p=31105

 

[Bob Larter]

Is there a group for repairing computer power supplies?..

No, but you're on-topic in here.
You can find lots of info about ATX power supplies here:

Question... I have the power supply out of the computer...
Besides pluging it in... how do you turn it 'on'...
The front panel on / off switch connects to the mother board..
How can I turn the power supply 'on' at the power supply?...

You need to ground the power-on signal, which is the green wire.
If you want to use the PSU as a bench supply, you can simply snip the
green wire from the back of the ATX connector, & solder a switch between
it & one of the black wires.

 

[Bob Larter]

Beware. It may not regulate properly with no load on the 5 or 12 V
output.

On every PSU I've tried it on, the fan seems to provide enough load for
the voltages to be okay.

 

[Baron]

Bob Larter Inscribed thus:

On every PSU I've tried it on, the fan seems to provide enough load
for the voltages to be okay.

A lot of the better ones have suitable loading built in ! More often
the PSU wont start up if it requires a minimum load, though some will
but don't regulate the output voltages properly. The regulation is
done with reference to the 5v rail, so that is the one that should be
loaded. Its wise to play safe and stick a load on anyway. I use a 10
ohm 10w resistor wired into a spare connector so that I can add or
remove it as needed. I also have a LED wired as well so that I
remember to switch off when working on an open case.

 

[PlainBill]

I fixed an ATX supply by replacing 2 very obviously bulged caps on the
output side with ones from a scrap Mobo !

Graham

That can work. I'm reaching the conclusion that the proce of caps is
so low (at least here in the USA) that it is better to replace all
caps with new quality caps. At one time I was using an approach
similar to yours. After a while I accumulated a number of power
supplies that APPEARED to work well with a dummy load, but when
connected to a motherboard the result was an unstable system.

Bulging caps are a good indication that a cap has failed. Not all
failed caps bulge.

PlainBill

 

[Eeyore]

Bob Larter Inscribed thus:

A lot of the better ones have suitable loading built in ! More often
the PSU wont start up if it requires a minimum load, though some will
but don't regulate the output voltages properly. The regulation is
done with reference to the 5v rail, so that is the one that should be
loaded. Its wise to play safe and stick a load on anyway. I use a 10
ohm 10w resistor wired into a spare connector so that I can add or
remove it as needed. I also have a LED wired as well so that I
remember to switch off when working on an open case.

I've heard of some where the feedback is taken as a mix of BOTH the 5V
and 12V loading. No guarantees though.

I agree that 'some' load on the 5V is likely best.

Graham

 

[Eeyore]

having a old boat anchor disk drive laying around to use as a dummy
load helps.....

Not a bad idea.

Remember the Full Height 5 1/4's ? They took about 30-40 W.

Graham

 

[Eeyore]

That can work.

The scrap mobo was Dell and used 'name' capacitors that still looked in
excellent condition ( get an ESR meter if you really need to know ), whereas
the bulged caps in the PSU were classic 'no name' off- brands.

I'm reaching the conclusion that the proce of caps is
so low (at least here in the USA) that it is better to replace all
caps with new quality caps. At one time I was using an approach
similar to yours. After a while I accumulated a number of power
supplies that APPEARED to work well with a dummy load, but when
connected to a motherboard the result was an unstable system.

The problem I've found is that the caps they tend to use are unusually small
( or odd ) form factors. Typically tall and very small diameter. Not many
stockists have them.

Bulging caps are a good indication that a cap has failed.

Absolutely. Guaranteed in fact.

Not all failed caps bulge.

Indeed. Also look for electrolyte leakage around the base. Usually a white
deposit. It's corrosive too, so when replacing, clean it away.

Graham

 

[Eeyore]

just fixed mine yesterday
replaceing the low imp caps on the
outputs.

Very typical.

Also on a Mobo, check the LV regulator caps around the CPU etc.

Graham

 

[Franc Zabkar]

A lot of the better ones have suitable loading built in ! More often
the PSU wont start up if it requires a minimum load, though some will
but don't regulate the output voltages properly. The regulation is
done with reference to the 5v rail ...

I haven't repaired many AT/ATX PSUs, but IME they usually (?) regulate
by sensing a weighted average of the +5V and +12V rails. This means
that the +5V and +12V rails move in opposite directions.

See
http://groups.google.com/group/alt.comp.hardware.pc-homebuilt/msg/f487f3cb92c489d5?dmode=source

- Franc Zabkar

 

[Baron]

I haven't repaired many AT/ATX PSUs, but IME they usually (?) regulate
by sensing a weighted average of the +5V and +12V rails. This means
that the +5V and +12V rails move in opposite directions.

See
http://groups.google.com/group/alt.comp.hardware.pc-homebuilt/msg/f487f3cb92c489d5?dmode=source

- Franc Zabkar

Hi Franc,
Yes I've seen that and noticed the effect. But since the 5 volt rail is
or used to be the most critical to circuit function that is the one
that is usually most heavily controlled. You can pull the 12 volt rail
voltage around quite a bit without much effect on the 5 volt one.

A 5 amp step load on the 12 volt rail (ignoring transients) has almost
no effect on the 5 volt rail. The reverse is not true though as you
show.

But its very much academic if the PSU is functioning correctly. Bad
caps seem to be very much the cause of most PSU ills judging by the
number that seem to blow up with regular monotony ! Though I don't
bother repairing them nowadays, it being more cost effective to throw
them in the scrap metal bin and fit a new one.