+/- 12V 4 pin connector query?

J

Juke

Geek Trainee
Does anyone know whether the +/- 12V 4 pin plug to the MB should have power on it when the computer is shut down?

The story is this - friends computer stopped running, not so much as a fan starting nor a beep from it. I suggested the PSU so he got a new replacement one. Still nothing.

I then thought he may have a MB problem, so we changed that. It combined with the new PSU or the old PSU still does nothing. Tried using a direct short on the start-up pins but still nothing. Tested the new PSU on my PC but my PC doesn't have the +/- 12V plug and it started fine. It says in the MB manual that if 12V is not present that the MB will not initiate a start. My only conclusion is that there should always be +/- 12v on regardless of the computers state (which on the new PSU and the old PSU there is not). Can anyone give me an alternative reason or confirm my conclusion?

Thank you
 
Juke said:
Does anyone know whether the +/- 12V 4 pin plug to the MB should have power on it when the computer is shut down?
Click to expand...
presumably you mean the 4 pin connector from the PSU to the mobo, correct ?

if yes, the new standard is ATX 2.2 (20 pin and 4 pin connectors) whereas older mobo's that conformed to ATX2.0 (a single 24 pin connecter) however some PSU manufacturers actually made a 24 pin connector where 4 pins are easily removable[ot]to make the PSU compatable with both ATX 2.0 & 2.2[/OT]

Juke said:
should there always be 12v on regardless of the computers state
Click to expand...
no, i don't know
 
If the system is on, then you should be able to get a reading on the voltage coming from the PSU. If not, then there's a problem.
 
The PSU has a power supply to it and as stated will run my PC which doesn't require the four pin connector. Nothing is happening on the problem system when the start button is pressed not even a bios check. To word my question differently, should there be 12V present on the 4 pin connector from the PSU to the MB with power being supplied to the PSU but the computer in a shut down state. (There is no choice in this state as the computer will not start under any conditions, even with just basics on the MB)
 
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