Dead AT power supply

[Ed Coolidge]

I have a slot1 PC that won't power on. My roommate reports that something
smelled burnt when it suddenly powered off. When I checked it out the system
would only power on for a short spurt then go dead after a second, so I'm
suspecting the PSU is shot. Unfortunately, the power connectors on the PSU
consist of 2 6pin connectors and a 3pin standby power connector. I'm assuming
that the unit is an AT model, but I don't know where to find one that has a
standby power connector. Any suggestions other than "buy a new PC" would be
appreciated.

 

[David Maynard]

I have a slot1 PC that won't power on. My roommate reports that
something smelled burnt when it suddenly powered off. When I checked it
out the system would only power on for a short spurt then go dead after
a second, so I'm suspecting the PSU is shot. Unfortunately, the power
connectors on the PSU consist of 2 6pin connectors and a 3pin standby
power connector. I'm assuming that the unit is an AT model, but I don't
know where to find one that has a standby power connector. Any
suggestions other than "buy a new PC" would be appreciated.

It's an AT PSU, from a particular manufacturer, but you gave no clue as to
who made the computer.

It could be the PSU or anything in the computer that's failed (CPU or
motherboard being common failure points in addition to the PSU) and
overloading it.

 

[Al Dykes]

I have a slot1 PC that won't power on. My roommate reports that something
smelled burnt when it suddenly powered off. When I checked it out the system
would only power on for a short spurt then go dead after a second, so I'm
suspecting the PSU is shot. Unfortunately, the power connectors on the PSU
consist of 2 6pin connectors and a 3pin standby power connector. I'm assuming
that the unit is an AT model, but I don't know where to find one that has a
standby power connector. Any suggestions other than "buy a new PC" would be
appreciated.

Dumpster, flea market, yard sale.

 

[Ed Coolidge]

The PC is an Acer Power 8000, or at least that's the best I can determine as
Acer has no record of the serial number. The only change that's been made was a
CPU upgrade that's been working fine for a month. I've unplugged all of the
drives and removed all of the cards except memory and video so I know it's not
overloaded. I tested it with the old CPU, but the results are the same. The PC
only has one 128MB RAM card and I don't have any spare RAM to test with it. I
tested the RAM a few weeks ago and it checked out OK. The power LED on the case
does light orange if that helps. I suspected that it might be the mainboard
too, but without swapping out the PSU I have no way to tell.

 

[Ed Coolidge]

Dumpster, flea market, yard sale.

Yes, but I don't believe that standby power connectors are common for AT units.
I would swap the PSU and the mainboard, but I don't know where to find a slot1
board on short notice as my roommate wants his PC back.

 

[Ed Coolidge]

Just a thought, is there any way to start the PSU without the mainboard? All it
should need is the right signal on the standby connector, but I'm not sure what
that would be.


David Maynard wrote:

 

[David Maynard]

Just a thought, is there any way to start the PSU without the
mainboard? All it should need is the right signal on the standby
connector, but I'm not sure what that would be.

There probably is but I can't find a pin out for the 3 pin connector, off hand.

You could try disconnecting the two 6 pin jobs and try powering it up with
the 3 pin still in the motherboard and hope the on/off switch works.

 

[David Maynard]

The PC is an Acer Power 8000, or at least that's the best I can
determine as Acer has no record of the serial number. The only change
that's been made was a CPU upgrade that's been working fine for a
month. I've unplugged all of the drives and removed all of the cards
except memory and video so I know it's not overloaded. I tested it with
the old CPU, but the results are the same. The PC only has one 128MB
RAM card and I don't have any spare RAM to test with it. I tested the
RAM a few weeks ago and it checked out OK. The power LED on the case
does light orange if that helps. I suspected that it might be the
mainboard too, but without swapping out the PSU I have no way to tell.

Well, I found the user manual for it and it shows the connectors on the
motherboard but, interestingly enough, it doesn't say to plug the 3 pinner
in when installing a PSU.

You may have to get one from an Acer distributor.

 

[Ed Coolidge]

I can't find any info on the pin out either. Just for kicks I checked it
without the 2 6pin connectors and the PSU fan starts up as soon as I connected
the power cord. The switch didn't make any difference. So if it's the
mainboard that's failed I would have to replace the PSU anyway.

David Maynard wrote:

 

[Ed Coolidge]

Again, just for kicks, I figured that if the PSU is indeed on when connected
with only the standby connector it should be able to power a drive, so I tried
connecting a CD drive. At first it just wouldn't budge, but then I thought that
having ground to the host controller might be the problem, so I tried it again
without the data cable. the drive spun up just fine and the tray worked too. So
what do you think, dead mainboard?

 

[David Maynard]

Again, just for kicks, I figured that if the PSU is indeed on when
connected with only the standby connector it should be able to power a
drive, so I tried connecting a CD drive. At first it just wouldn't
budge, but then I thought that having ground to the host controller
might be the problem, so I tried it again without the data cable. the
drive spun up just fine and the tray worked too. So what do you think,
dead mainboard?

Sounds like either that or the processor.

If it's the main board I'd bet it's either the Vcore regulator or caps.
Check the large caps around the CPU to see if any are bulged or leaking.

Also, try power the mainboard with no CPU, memory, or anything. It won't
run, of course, but the point is to see if the PSU will stay up.

 

[Ed Coolidge]

Well, I've already tried using the old processor, which I know is still good.
I've pulled everything and still no go. There's a row of 4 caps behind the slot
that are bulging on top. I guess it's time to pull the cover over this patient.

BTW, a main board won't start without a CPU. Once I mounted an AMD Tbird
without locking the socket first (and yes, the heatsink was small enough to
clear the level).

 

[spodosaurus]

Well, I've already tried using the old processor, which I know is still
good. I've pulled everything and still no go. There's a row of 4 caps
behind the slot that are bulging on top.

You could always have a go at replacing them. If you're going to junk it
anyway, where's the harm?

I guess it's time to pull the
cover over this patient.

BTW, a main board won't start without a CPU. Once I mounted an AMD
Tbird without locking the socket first (and yes, the heatsink was small
enough to clear the level).

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http://www.abmdr.org.au/
http://www.marrow.org/

 

[Ed Coolidge]

At this point I'm not sure if it's worth trouble. I'm not that good at
soldering anyway.

 

[David Maynard]

Well, I've already tried using the old processor, which I know is still
good. I've pulled everything and still no go. There's a row of 4 caps
behind the slot that are bulging on top. I guess it's time to pull the
cover over this patient.

The bulging caps are certainly bad. Whether they took the regulator too, or
it took them, or they simply went on their own you can't tell just by looking.

I'd replace them but then not everyone is comfortable soldering.

Actually, the first thing I would do is simply pry them off; which isn't as
hard as it might seem as the wires will pull out of the cap case. And then
I'd try powering the board up with no processor, memory, or anything else
in it. If it doesn't crowbar the PSU then there's a decent chance the Vcore
reg is ok and replacing the caps alone might fix it. If it still crowbars
the PSU then the Vcore FET is likely gone and I'd replace that too.

BTW, a main board won't start without a CPU.

That's why I said "It won't run, of course"

 

[Ed Coolidge]

The bulging caps are certainly bad. Whether they took the regulator too,
or it took them, or they simply went on their own you can't tell just by
looking.

I'd replace them but then not everyone is comfortable soldering.

I think I'll just face the fact that it's dead and leave it at that. It's not
that I'm uncomfortable with soldering, but rather not very good at it. I'll
check the local shops for used parts.

That's why I said "It won't run, of course"

I'm mean nothing would start, not even the PSU. There's no point in testing
something when it's not going to do anything.

 

[David Maynard]

I think I'll just face the fact that it's dead and leave it at that.
It's not that I'm uncomfortable with soldering, but rather not very good
at it. I'll check the local shops for used parts.

Entirely your choice.

I'm mean nothing would start, not even the PSU. There's no point in
testing something when it's not going to do anything.

I don't know if there's something 'special' about your motherboard, besides
being broke at the moment, but every one I've got powers up without CPU,
memory, or anything else, installed and I regularly check for shorted
mobos, and Vcore/mem voltages, that way rather than risk CPU and memory on
the first debug power up.

 

[Ed Coolidge]

I don't know if there's something 'special' about your motherboard,
besides being broke at the moment, but every one I've got powers up
without CPU, memory, or anything else, installed and I regularly check
for shorted mobos, and Vcore/mem voltages, that way rather than risk CPU
and memory on the first debug power up.

The busted one is a slot1, which obviously doesn't have a socket.

 

[David Maynard]

The busted one is a slot1, which obviously doesn't have a socket.

Doesn't matter. I do the same with slot-1 boards with the same results.

Actually, you can think of the slot as a kind of 'linear socket'. The
reason for the cartridge was to fit the cache chips on-board and later they
went on-die with the coppermines, so it again fit in a socket form factor,
but the bus interface, I.E. the lines to the socket/slot, are essentially
the same (sans some termination resistors and decoupling caps); which is
why slotkets work.

The thing is, the processor and memory are not involved in the PSU
power-on/off circuit.

 

[Ed Coolidge]

I know what a slot interface is, why they were used and why they are were phased
out. However, you missed the obvious point that I wasn't even talking about the
mainboard that died. The one that died was a Slot 1 and the other that I was
referring to has a socket, Socket A to be exact. And no the PSU would not even
start without the CPU. BTW the Socket A mainboard works just fine has I'm using
it right now.