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Power Supply doesnt have -5V, Does motherboard need?

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March 21, 2009 7:56:29 PM

Hi Everyone,

i'm building my own PC for the very first time, however I am an Electrical Engineer so I do have some knowledge about some things. I am using the PPCS500 power supply, and the Gigabyte GA-EP45-DS3L motherboard. I turn the system on and the power supply doesnt seem to boot and nothing else seems to turn on. The switch on the front case is activating when pressed (checked with multimeter) and appears to be going to right place.

I disconnected power to all peripherals except motherboard where its connected to the ATX connector (2x12) and 4 pins on the 8 pins of the power connector (according to the manual from the power supply).

One 'Aha!' that I noticed is that the power supply does NOT have a -5V rail, but it looks like the motherboard expects it. Could that be why my system is not turning on?

I guess i"m a little confused because I chose teh same components as the "Toms Hardware $625 gaming build" from recently and somehow they got it to work. Oversight on their part? Any other ideas?
a c 139 ) Power supply
a b V Motherboard
March 21, 2009 11:40:08 PM

I think the -5v supply became optional when the old ISA slots on the motherboards went away.

Is there a power switch on the back of the PC P&C 500?
March 22, 2009 10:53:44 AM

WR2 said:
I think the -5v supply became optional when the old ISA slots on the motherboards went away.

Is there a power switch on the back of the PC P&C 500?


There is no power switch on the back of the system. There's a label that says "Full Range 100-240 VAC" so it appears that it automatically switches. If you mean the ON/OFF switch on the power supply, then yes, I have it set to "1" to have it on.

Any other suggestions I can try?
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a c 144 ) Power supply
a c 156 V Motherboard
March 22, 2009 11:19:13 AM

MY GA-EP35-DS3P works just fine without the -5 volts from the PSU. I also have an eVGA 680i board that doesn't need -5 volts.

OK. Try this checklist:
http://www.tomshardware.com/forum/261145-31-build-post-...

If that doesn't help:
Pull everything except the CPU and HSF. Boot. You should hear a series of long single beeps indicating memory problems. Silence here indicates, in probable order, a bad PSU, motherboard, or CPU - or a bad installation where something is shorting and shutting down the PSU.

To eliminate the possiblility of a bad installation where something is shorting and shutting down the PSU, you will need to pull the motherboard out of the case and reassemble the components on an insulated surface. This is called "breadboarding" - from the 1920's homebrew radio days. I always breadboard a new or recycled build. It lets me test components before I go through the trouble of installing them in a case.

If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM is shorting out the PSU (very rare). Long single beeps indicates that the BIOS does not recognize the presence of the RAM.

If you get the one long and two or three short beeps, test the rest of the RAM. If good, install the video card and any needed power cables and plug in the monitor. If the video card is good, the system should successfully POST (one short beep, usually) and you will see the boot screen and messages.

Note - an inadequate PSU will cause a failure here or any step later.
Note - you do not need drives or a keyboard to successfully POST (generally a single short beep).

If you successfully POST, start plugging in the rest of the components, one at a time.

For a somewhat extreme example of breadboarding (well, more like building a PC without a case):
http://www.tomshardware.co.uk/forum/page-262730_13_0.ht...

March 22, 2009 11:48:46 AM

jsc said:
MY GA-EP35-DS3P works just fine without the -5 volts from the PSU. I also have an eVGA 680i board that doesn't need -5 volts.

OK. Try this checklist:
http://www.tomshardware.com/forum/261145-31-build-post-...

If that doesn't help:
Pull everything except the CPU and HSF. Boot. You should hear a series of long single beeps indicating memory problems. Silence here indicates, in probable order, a bad PSU, motherboard, or CPU - or a bad installation where something is shorting and shutting down the PSU.

To eliminate the possiblility of a bad installation where something is shorting and shutting down the PSU, you will need to pull the motherboard out of the case and reassemble the components on an insulated surface. This is called "breadboarding" - from the 1920's homebrew radio days. I always breadboard a new or recycled build. It lets me test components before I go through the trouble of installing them in a case.

If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM is shorting out the PSU (very rare). Long single beeps indicates that the BIOS does not recognize the presence of the RAM.

If you get the one long and two or three short beeps, test the rest of the RAM. If good, install the video card and any needed power cables and plug in the monitor. If the video card is good, the system should successfully POST (one short beep, usually) and you will see the boot screen and messages.

Note - an inadequate PSU will cause a failure here or any step later.
Note - you do not need drives or a keyboard to successfully POST (generally a single short beep).

If you successfully POST, start plugging in the rest of the components, one at a time.

For a somewhat extreme example of breadboarding (well, more like building a PC without a case):
http://www.tomshardware.co.uk/forum/page-262730_13_0.ht...



I took out the power supply from my computer case, and connected it to the wall. I shorted the green wire to a black wire with a paperclip and turned the power supply ON. The fan didnt turn on (which I assume should always turn on, and is not controlled by M-board, right?). With my voltmeter I didnt get any 12V signal on the yellow wire (with respect to the black ground wire). It seems that the power supply is gone. Is there anything I did wrong with the power supply test? Should I try anything else?
a c 139 ) Power supply
a b V Motherboard
March 22, 2009 12:05:35 PM

You can jumper the Green wire (PSU-On pin 16) with one of the Black (Ground) wires and the PSU should power on.
ATX V2 pin out spec
a c 139 ) Power supply
a b V Motherboard
March 22, 2009 12:08:10 PM

Whoops. Yeah, not much else you can try. Sounds like a probable shipping casualty.
I've read that up to one item in 10 (10%) of parts in a home build suffers from being DOA or "infant mortality".

edit;
actually I think that 10% was a return rate for ALL reasons, not just being DOA or failed after a short time.
March 22, 2009 12:08:17 PM

I did jumper the Green wire to one of the black wires. The PSU did not turn on as far as I can tell. The PSU fan didnt turn on, and no voltage measured on the Yellow wire. I even took the PSU out of the case for this test. Is it pretty certain that PSU is dead?
!