PSU 8pin -> 4 Pin question

Greboth · 22 Nov 2010 at 19:52

PSU Queries

Hi all

Just want to double check this as never had the problem before. I am installing a new psu into an older machine, the psu 12v CPU power is 8 pin, however the motherboard is 4 pin.

As far as I understand it looking end on the 8 pin is
ground 12v
ground 12v
ground 12v
ground 12v

and 4 pin is
ground 12v
ground 12v

So I cant see any problem with only plugging half of the 8 pins into the motherboard but just want to check first.

Thanks, greboth.

95thrifles · 22 Nov 2010 at 19:54

Normally whilst they are 8 pin, theyre made up of 2 sets of 4 pins and you should be able to separate them?

Boozebeard · 22 Nov 2010 at 19:58

well I had to do the opposite of that once; had to plug a psu with only a 4 pin connector into a mobo with an 8pin socket and it worked so I think it should be fine.

Greboth · 22 Nov 2010 at 20:12

95thrifles, no I had hoped it would be but it isn't.

I realised as well I have a 8 pin extension which does split. Looking at that and thinking about it some more should be fine as the ones that do split you are effectively only plugging in half of the 8 pin.

Greboth · 22 Nov 2010 at 20:58

Ok double post I know, PC powered up fine quick check it was up functioning and now doing some cable tidying and just noticed the 24pin is missing pin 8 (which google tells me is pwr_on) Only thing I can find useful on pwr on is

PWR_OK signal has nothing to do on ther controlling of ATX power supply operation. PWR_OK is an output from the supply. "PWR_OK is a "power good" signal. It should be asserted high by the power supply to indicate that the +12 VDC, +5VDC, and +3.3VDC outputs are above the undervoltage thresholds.

which if I have this right suggests that without the pin 8 there is no way to tell if the 12V, 5V, 3.3V are within the % tolerances but doesn't per se power anything or affect the operation of the psu so I am assuming it is possible to run a rig without it. Assumption correct?

Sorry for the questions, don't build many pc's and this is not something I have come across before.

95thrifles · 22 Nov 2010 at 21:01

What PSU is it and what mobo?

Greboth · 22 Nov 2010 at 21:08

Sorry, Enermax 535W eg565ax-ve and Gigabyte socket 775 GA EP41-UD3L. Regarding the PSU, the stock photos show it is missing so I can only assume it isn't a problem without it but just seems odd to be missing it.