Question Computer won't start, PSU tester shows 3.3V and 5V rails fluctuating a lot

Sep 22, 2019
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My computer recently stopped booting - when I turn it on the CPU fan starts and the lights flash, but nothing happens. After 1 minute (almost exactly, every time), it shuts off.

So far I've tried another RAM stick (no luck) and picked up a PSU tester (this one: https://www.amazon.com/Optimal-Shop-Computer-Supply-Connectors/dp/B00Q8SUYHW/ ). The PSU tester shows everything normal except the 5V rail fluctuates between 4.9, 5.1, and HH (the tester's way of saying "too high"), and the 3.3V fluctuates between 3.1, 3.4, and HH.

Is that enough evidence to buy a new power supply?

Here are my specs:
CPU: Intel Core i3 4330 Dual Core 3.5GHZ
CPU Cooler: Noctua NH-L9i Low Profile CPU Cooler
RAM: 8GB Crucial Ballistix Sport
Hard Drive: Plextor 128GB mSATA SSD
Motherboard: ASRock Z87E-ITX Mini ITX
Case: Realan E-I7 + USB 3.0 Upgrade
Power Supply: 12V 180W DC / 12V 7A (120W) AC Adapter Upgrade
 

jonnyguru

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What is the power supply?

You list it as an AC adapter, but an AC adapter is only going to have one voltage. If it's a 12V adapter (as you list) it's not providing +3.3V and +5V, so how are you measuring that? Are you using a PICO PSU attached to the adapter? If so, what is the PICO PSU?
 

jonnyguru

Distinguished
Ok.

Acceptable +3.3V and +5V fluctuations are +/- 10%. You're nowhere near that. So I doubt it's a PSU issue.

Remember your RAM works at 1.35V, which is regulated by the motherboard, so the problem is probably the motherboard.

If you POST without RAM, do you at least get the "no RAM" error code?
 
Sep 22, 2019
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The tester doesn't display the actual voltage when it's out of the normal range, it just displays "LL" for low and "HH" for high. Even though the 3.3 and 5 readings bounce around between acceptable numbers they also display HH every once in a while, so wasn't sure if I should worry about that.

Nothing is appearing on the screen but I'll test removing the RAM and see if it gives any beep codes, thanks.
 

jonnyguru

Distinguished
The tester doesn't display the actual voltage when it's out of the normal range, it just displays "LL" for low and "HH" for high. Even though the 3.3 and 5 readings bounce around between acceptable numbers they also display HH every once in a while, so wasn't sure if I should worry about that.

Nothing is appearing on the screen but I'll test removing the RAM and see if it gives any beep codes, thanks.
Oh.. Ok. A DMM might be more helpful, but if it's THAT far out of range, you might need to replace the PICO PSU. Not that PICO PSUs are that expensive...
 

jonnyguru

Distinguished
The tester doesn't display the actual voltage when it's out of the normal range, it just displays "LL" for low and "HH" for high. Even though the 3.3 and 5 readings bounce around between acceptable numbers they also display HH every once in a while, so wasn't sure if I should worry about that.

Nothing is appearing on the screen but I'll test removing the RAM and see if it gives any beep codes, thanks.
Oh.. Ok. A DMM might be more helpful, but if it's THAT far out of range, you might need to replace the PICO PSU. Not that PICO PSUs are that expensive...
 

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