4.5V on 5V rail (Antec TC550) - computer won't boot

After weeks of running without a single crash, the first system listed in my sig crashed and now won't load windows. It goes into a continuous reboot cycle when trying load the windows gui. I've tinkered with it off and on for several days with no real success. Last night I was looking at the voltages in the BIOS and saw the 5V line reading a measely 4.5V. The POT on the True Control panel for the psu was turned all the way to the max, and I turned it up and down to make sure it was still working. I can adjust the 5V line lower, but can't raise it above 4.5V.

So now I'm trying to decide if the problem lies with my psu or my motherboard. I didn't have a multimeter with me last night to check the readings of one of the molex connectors, but I will take one home with me tonight. Unfortunatley from the info I gathered, my Asus A7N8X-Deluxe v2.0 motherboard derives the cpu current from the 5 volt rail as does the 9800 video card.

I've already reset the computer back to stock speed and even replaced the 9800 with an old Geforce3 Ti200 card, but it still won't boot windows and the 5 volt rail won't budge above 4.5V.

Is this most likely a psu problem or is it possible that the motherboard is at fault here? I've got a FSP 350 psu in another computer that I could disassemble and test with, but that's gonna be a lot of work since I just recently spent over an hour routing cables for the FSP 350 and hiding them. So I was thinking about just buying another psu and if that fixes things, sending the Antec TC550 to be serviced or replaced. But before I spend the money on another psu, I wanted some opinions from forum members.

I'll post the multimeter readings this evening.

Can't really say if it's a psu or mobo problem unless you get readings with a DMM.

That's what I'm thinking.

I can say for sure that previously the 5V rail was a solid 5.0x volts in the BIOS.

I will post DMM reading in a few hours.

Okay, got some readings with the DMM. At first boot, the DMM showed 5.03V and then started falling. After about 1 minute on the bios screen, the BIOS showed 4.30V and the DMM read 4.41V. So does pretty much indicate the psu is the culprit?

Ugh, that sucks.

Souds like a faulty PSU to me... Never used the TC, can you use it without the panel and see how it reads?

Yep, that psu is a goner RMA that sucka back to antec and get a Fortron or a sparkle.

canadianpsycho said:

Ugh, that sucks.

Souds like a faulty PSU to me... Never used the TC, can you use it without the panel and see how it reads?

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Naw, without the controller connected, the psu operates each rail (+3.3, +5, +12) at the minimum of the voltage range, which is too low to be stable.

Originally posted by Nebulous

Yep, that psu is a goner RMA that sucka back to antec and get a Fortron or a sparkle.

Click to expand...

I'll be happy if they just replace the TC550. Antec is not gonna send me another brand PSU at my request or give me monetary compensation, and I can't justify spending the money out of pocket on another PSU. I just hope the next one is a little more reliable. This one lasted about 9 months.

Mustanley said:

I'll be happy if they just replace the TC550. Antec is not gonna send me another brand PSU at my request or give me monetary compensation, and I can't justify spending the money out of pocket on another PSU. I just hope the next one is a little more reliable. This one lasted about 9 months.

Click to expand...

At least you have a 3 year warranty. Also, it could have been worse and failed taking something with it.

It sounds like the controller circuit has failed. Defaulting to the low end without the controller is on purpose on their part. They are trying to be cautious with this. You would think they would default to closer to nominal voltages.

I had similar symptoms with an Antec SL400. I never checked the voltages but the system was unstable and would not boot. I turned out it was the new CDRW I just installed. Because of poor design power was shorted if you put screws in the rear upper holes. The SL400 got too hot to touch when the CDRW was shorted. Fortunately moving the screws solved the problem with nothing harmed.