What happens after plugging in 6+2 pin power cable into 2x4pin for CPU into motherboard?

Question

I plugged in 6+2 pin power wire coming from PSU that is meant for Graphics Card into 8-pin socket (atx 12v 2x4) on the motherboard that powers CPU. The pins fitted normally and I didn't suspect anything. The PSU has short circuit protection (and OVP and UVP) and the computer didn't start, however there probably was a short circuit that lasted a small amount of time.

Can this break the PSU and/or motherbooard? Because I'm having errors that cause windows to restart with the error message: windows must restart because the power service terminated

Solution

You can't easily put a 8 pin PCIe power cable into a 8 pin EPS 12V MB connector, they are keyed differently.

Both of the cables contain only +12V and Ground lines, due to some really unfortunate decision making by the PCI-SIG, the pin assignments are opposite each other which means that you were driving +12V into the motherboards ground; see the image below.

An ATX power supply is required to provide short circuit protection:

An output short circuit is defined as any output impedance of less than 0.1 ohms. The power supply shall shut down and latch off for shorting the +3.3 VDC, +5 VDC, or +12 VDC rails to return or any other rail

The voltage regulator circuit (aka voltage regulator module) on your motherboard took the 'brunt' of the reversed polarity on the ground plane. How much protection that circuit has from an event like this varies from model to model - there is no standard. The good news is that components in this circuit are easy to troubleshoot with home electrical equipment (multimeter), and can be repaired. The bad news is that if you can't do the repair yourself (need solid soldering skills), the cost to get it repaired will be around the same price as a new motherboard.

See this link for additional info on a motherboards voltage regulator circuit

Comments

[iSR5]

if your PSU has OVP/UVP protection, then it will shut down that rail before the voltages go more or less than the socket needed (which I think it did with yours since everything is working). IF NOT, You wouldn't probably have a working computer to post a question in the first place ! .. I highly recommend that you re-check your wiring, and use BIOS diagnostic tools to scan your hardware functionality.

[Baltar]

There are only 24-pin wire into the mainboard and 2x4pin into the mainboard for CPU. Nothing else is connected in terms of power to mainboard. SATA cables are impossible to connect wrong, I'm pretty sure everything is alright in terms of wiring. If I didn't break the mainboard, then I wonder what caused the forced restart that Windows had to do?

[Baltar]

The answer tells what I asked. What happens after plugging in 6+2 pin power cable into 2x4pin for CPU into motherboard. The answer is short circuit and voltage regulator circuit taking the brunt. I don't understand why this question is considered too broad, since it has exact answer. Maybe I didn't tell exact model of PSU and motherboard, but it's a short circuit no matter what motherboard you have if you put these cables like I did.

[Dan Is Fiddling By Firelight]

FWIW I made a similar mistake once (6 pin into 4 pin). The PSU refused to power on even momentarily for a few minutes afterward; but afterward and with the connection corrected the system ran for several more years. This was with a high end mobo and PSU, I wouldn't be surprised if cheaper or less lucky hardware sustained fatal damage before the short circuit detection components could shut everything down.

[Baltar]

Thank you for detailed answer, that's exactly what I wanted to know. So it's The voltage regulator circuit on motherboard took the 'brunt'. Do you think nothing bad happened to PSU, since it has protections?

[Baltar]

You answer tells what I asked. What happens after plugging in 6+2 pin power cable into 2x4pin for CPU into motherboard. The answer is short circuit and voltage regulator circuit taking the brunt. I don't understand why this question is considered too broad, since it has exact answer. Maybe I didn't tell exact model of PSU and motherboard, but it's a short circuit no matter what motherboard you have if you put these cables like I did.

[Argonauts]

I agree; there is a question from a few years ago where someone plugged the eps into their graphics card and it wasn't characterized as too broad. In any event hopefully the info helps.

[rayzinnz]

"You can't easily put a 8 pin PCIe power cable into a 8 pin EPS 12V MB connector, they are keyed differently." - your first sentence is 100% wrong - look at the diagram again, the beveled edge keys fit easily into the square keys.