Incorrect Voltage on 4-pin CPU connector?

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Zeon

3916 posts

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#240460 9-Sep-2018 10:44

Hey guys,

So I bought a new PC from PB Tech. I wanted to buy the components and test them out as partly its been a while since I've tinkered with this stuff and I wanted to see I was happy before making a big order for tech refresh all of our computers at the office.

I am having a problem where the computer will instantly turn off if the CPU 12v connector is plugged in. I checked with the multimeter and its only supplying 5v rather than the 12v I would expect on the 4 pin connector. I am using the Silverstone SX500-g modular power supply and there is the additional 4 pin for CPU which comes daisy chained off the motherboard connector (20+4 pin) which I was using.

I have just managed to get it to boot by using the PCI-E connector plugged into the CPU power to work. Is this a faulty power supply or am I doing something wrong? This is the first time I've ever used a modular power supply.

4 pin connector daisy chained from MOBO connector:

PCI-E connector where it now successfully boots:

Speedtest 2019-10-14

cruxis

481 posts

Ultimate Geek

#2086373 9-Sep-2018 11:19

2 way is correct, When connecting a 20+4 pin ATX PSU to a 20 socket Motherboard the extra 4 pins are unused, left hanging. Generally it should not have been able to reach the CPU 4 pin, Also it would not have that little clip thingy.

Info

https://www.smps.us/20-to-24pin-atx.html

Many new ATX12V v2 compliant PC power supplies come with a dual 24/20 (sometimes called 20+4) connector for backward compatibility. It has the last four pins on a detachable section that slips out, so you can plug it into an older motherboard (see the diagram above). Just don't plug the remaining 4-pin piece anywhere- it is not compatible with any other circuits! If your PSU happens to have a solid 24-pin connector, you can still try to insert it into 20-pin slot with the last four pins hanging over the edge of the board's connector

Zeon

3916 posts

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#2086567 9-Sep-2018 19:17

cruxis:

2 way is correct, When connecting a 20+4 pin ATX PSU to a 20 socket Motherboard the extra 4 pins are unused, left hanging. Generally it should not have been able to reach the CPU 4 pin, Also it would not have that little clip thingy.

Info

https://www.smps.us/20-to-24pin-atx.html

Many new ATX12V v2 compliant PC power supplies come with a dual 24/20 (sometimes called 20+4) connector for backward compatibility. It has the last four pins on a detachable section that slips out, so you can plug it into an older motherboard (see the diagram above). Just don't plug the remaining 4-pin piece anywhere- it is not compatible with any other circuits! If your PSU happens to have a solid 24-pin connector, you can still try to insert it into 20-pin slot with the last four pins hanging over the edge of the board's connector

Ah thanks for the explanation!

Speedtest 2019-10-14

Tzoi

424 posts

Ultimate Geek

#2086625 9-Sep-2018 21:26

You shouldn't be plugging in the PCI-E connector into the CPU power socket, there should be a separate CPU power cord (EPS) and connector on the PSU

Batman

Mad Scientist
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#2086656 10-Sep-2018 06:58

A reminder to self of why I shouldn't build my next computer. Won't stop me from from diy upgrade parts though!

SpartanVXL

1309 posts

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#2087649 11-Sep-2018 16:17

You aren't actually using the pci-e power. From what I can see in the diagram on the PSU, you've plugged in the correct EPS(black) 8 pin(4+4). The pci-e power ports the are blue 8 pins (6+2). The other black 6pins are for sata/molex.

It been a while since i've seen a mobo only accept 20 pin for atx. All mobos in last 5 years i've seen have always been 24pin, even though they keep the 20+4pin legacy compatability.

Coil

6614 posts

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#2087690 11-Sep-2018 17:22

Ahh the joys of cheap modular power cables....
Lucky you didn't do any damage as far we know..