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New RM850e issue with older motherboard

Go to solution Solved by dmonds,

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Hi there,

After upgradingmy 11 year old PC, I've gifted my son my old ASUS Z87-c Motherboard, i7-4770k, G.Skill 16GB RAM kit to build his first gaming PC.

I've had the hardware since new and it's never skipped a beat since I built it in 2013.

He's bought himself a new case and PSU (RM850e).
However on powerup, the CPU Fault LED on the old motherboard comes hard on.

I have seen this in other known good mobo/CPU PCs when either the 24 pin or "CPU" power connectors are not inserted properly.

If I plug my original HX750 PSU in, the motherboard powers up fine, so it is not the CPU.

If I plug his new PSU into my new motherboard, it also powers up ok.

I've tested both power supplies with a digital multimeter and everything seems fine, except...

The new PSU does not have the single -12V pin populated in its 24 pin motherboard cable.

Could this be causing the issue, or is it some other form of incompatibility?

Thanks in advance for any advice offered.

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the -12V supply hasn't been used since the 90's probably, it was for the serial ports, and is optional now in the ATX spec. Most PSUs don't even have a wire for that one nowadays.

When you tried the RMe on the old PC, did you use the cables that comes with it?

I've seen some inventive people manage to shove a PCIE power cable in CPU EPS12V sockets so maybe make sure that wasn't done by mistake ^^

Otherwise there's been no change at all in pinouts or voltages. the RMe should work fine even on hardware older than that.

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  • Solution

Hi, thanks for your reply.

Yes, I used the correct cables which came with the PSU.

The old motherboard was new in 2013.
The only difference I can work out is that my old HX750 has the -12v and the new RM850e does not.

The motherboard does have a COM port header on the motherboard itself, so that's likely why it's throwing an error.

I guess my son has some choices to make and needs to see if we can find a new PSU which comes with a -12v pin.


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