Troubleshooting - power supply?

  • Thread starter Thread starter Dan Seur
  • Start date Start date
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Dan Seur

A machine here has failed at power on. No box activity whatsoever, no
fans or lights. This includes the power supply fan. The wall power
source is good.

I've concluded it's probably either the power supply or a mainboard
blowout, neither of which is much of a problem to me, and pulled the
power supply. No fan activity when it's plugged into the wall and turned
on.

Does anyone know whether a standard ATX power supply should show signs
of life when turned on, if it's not plugged into an ATX board? I can't
find this nugget of info on the web and my handy little shop around the
corner is closed for the weekend. Sure would simplify life if I knew.

I don't have any useful instruments, and I'd hate to blow another
mainboard (which could happen for any number of reasons, including a
shorting peripheral reaching out and zapping everything) or blow another
power supply (ditto) just by ignorant replacement. I'll of course truck
the system down to the my pal at the corner store if necessary, but
maybe I can clean this problem up easily and quickly without resorting
to that.

Any guidance on that specific power supply question?
 
Dan Seur said:
A machine here has failed at power on. No box activity whatsoever, no
fans or lights. This includes the power supply fan. The wall power
source is good.

I've concluded it's probably either the power supply or a mainboard
blowout, neither of which is much of a problem to me, and pulled the
power supply. No fan activity when it's plugged into the wall and turned
on.

Does anyone know whether a standard ATX power supply should show signs
of life when turned on, if it's not plugged into an ATX board?
Click to expand...

AFAIK, no.

It will not.

You need something like this:

http://www.cyberguys.com/templates/searchdetail.asp?T1=115+3112

I've had more than the usual amt. of dead PSU's lately due
to the "defective electrolytic cap paste" issue of
a couple years ago...the PSU's mgfd. with these defective
caps are starting to fail (pretty spectacularly-bits of
paper from blown-up electro all over inside of PSU).
 
Dan Seur said:
A machine here has failed at power on. No box activity whatsoever, no
fans or lights. This includes the power supply fan. The wall power
source is good.

I've concluded it's probably either the power supply or a mainboard
blowout, neither of which is much of a problem to me, and pulled the
power supply. No fan activity when it's plugged into the wall and turned
on.

Does anyone know whether a standard ATX power supply should show signs
of life when turned on, if it's not plugged into an ATX board? I can't
find this nugget of info on the web and my handy little shop around the
corner is closed for the weekend. Sure would simplify life if I knew.

I don't have any useful instruments, and I'd hate to blow another
mainboard (which could happen for any number of reasons, including a
shorting peripheral reaching out and zapping everything) or blow another
power supply (ditto) just by ignorant replacement. I'll of course truck
the system down to the my pal at the corner store if necessary, but
maybe I can clean this problem up easily and quickly without resorting
to that.

Any guidance on that specific power supply question?
Click to expand...

ATX standards from formfactors.org:

http://www.formfactors.org/developer/specs/ATX_ATX12V_PS_1_1.pdf

Some PSU's require a load demand, others don't. More often than not these
days, they DO require a load demand. If the PSU is plugged into a
motherboard, even a dead motherboard ('cus they're never completely dead),
there will be enough load demand to allow you to use a VOM and check the
voltages of the various pins or to kick the PSU's fan assuming the fan isn't
dead. (You'll find thepin-out specs in the PDF I referenced above.) Beg,
borrow or steal a VOM and check the pins if you really want to be sure. They
cost about the same as the PSU.

I'd say the PSU is dead.

It's kind of hard to blow a PSU with static charges or backwash from
peripherals. PSU's die out of age (the fan fails causing the unit to
overheat and have a meltdown) or when God reaches out and touches one
(lightning strike). More often the former than the latter.
 
My experience is that power supplies have an interlock
with the mainboard and will not switch on when removed
from the MB. Unfortunately I discovered this after
replacing two good power supplies.
 
Dan Seur said:
Does anyone know whether a standard ATX power supply should show signs
of life when turned on, if it's not plugged into an ATX board? I can't
find this nugget of info on the web and my handy little shop around the
corner is closed for the weekend. Sure would simplify life if I knew.
Click to expand...

No, ATX PSUs are switched mode power supplies and require a PS_ON#
signal from the motherboard to power-up.


--
 
Using an insulated wire stripped at both ends, insert one end into the PS
connector at the Green wire and connect the other end to any Black wire. In
other words, jumper the Green wire to any Black wire. Plug it in and turn it
on. If'n it's any good at all, the fan will come on.
 
I posted this query around 6:30 last night Florida time, had dinner &
fooled around, checked back at 11PM, and found 5 responses. I'm very
grateful to all 5 of you.

I had earlier checked the ATX PS specs at a couple websites, Mynd, & not
found the little nugget I needed - probably just missed it like I often
do. I also appreciate the wisdom & war stories from you Vance, Stewart,
and Paul.

For what it's worth, I had also done the sniff test that nobody
mentioned; I had a PS failure on a bigger machine about a year ago but
didn't know it - another quiet one - and when I lugged the tower to a
shop, the tech stuck his nose in the case and smelled the burnout. I
felt like a dope. This time, no smell.

This morning I did what Colon suggested - shorted the green and a black
wire on the PS's mainboard connector, got no fan action, ran out for a
new PS, and presto - good old HOM3 is humming along online again. Thanks
again to all, and a tip of the hat to you, Colon, for your simple and
quick diagnostic. :-)
 
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