Question Installed new PSU and pc wont boot now

Sep 10, 2020
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Hey guys I am posting on here for a buddy of mine whos PC has had some of the weirdest issues I have ever encountered in the 30+ systems ive built. Im in a different state so I cant be there in person to help him so we face time and I walk him through step by step what to do. So he started getting a Critical_Process_Died randomly in demanding games and we spent 6+ hours troubleshooting and to no eval the problem got worse to where it would crash if he would watch videos. We narrowed it down to a potential power supply issue and he ordered a Corsair RM750x. A friend of ours went over to install it since he isn't the most tech savvy and when he swapped over the new power supply the PC would boot for half a second, fans would spin and then there would be a click and it would turn off. He then put all the old psu cable and psu back and now the pc does the same exact thing where it would turn on for 1/2 a second with fans spinning and "click" and it will die. I spent 4 hours today walking my friend through troubleshooting.

Tried

1. Old power supply with old cables. didnt boot

2. New power supply with new cables. didnt boot.

3. CMOS battery change. Didnt boot.

4. Bare minimum boot attempt with cpu, cooler and m.2 no gpu. Didnt boot.

5. reseated gpu. didnt boot

6. reseated RAM. didnt boot.

7. 1 stick of ram. didnt boot.

8. 0 ram. didnt boot.

9. re-seated all connections. Didnt boot

10. Power supply tested the new psu and only the +5vsb light came on

11. did the paper clip test on the new psu and it spun up just fine.

12. Tried combinations of new and old cables on both PSU. Didnt boot.

Tomorrow he will be dissembling the entire PC and building it back from scratch to find the issue. If you guys have any ideas it would be greatly appreciated.

Full Build:

CPU: i7-8700k (not overclocked)

MOBO: Asus Prime Z370-A

Ram: G.Skill Ripjaws V series 32GB, 3200. F4-3200C16D-32GVK

GPU: MSI RTX 2070 Super Gaming X

Cooler: cooler master masterliquid lc240e

PSU: (old) Rosewill 750w Quark series 80 plus platinum. (New) Corsair RM750x.

m.2: samsung m.2 dont know what kind

HDD: 2tb WD black
 

mdd1963

Polypheme
I'd try to find out if he first tried using the NEW PSU with old cables by mistake... (as the PSU's insertion side pinouts vary massively from one PSU to the next, if old modular cables used with new PSU, things can get very...BAD...and quickly!)
 
Sep 10, 2020
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I'd try to find out if he first tried using the NEW PSU with old cables by mistake... (as the PSU's insertion side pinouts vary massively from one PSU to the next, if old modular cables used with new PSU, things can get very...BAD...and quickly!)
He couldn't use the old 24pin on the new PSU but we did try using the old GPU and CPU cables since they matched up.
 

DSzymborski

Polypheme
Moderator
He couldn't use the old 24pin on the new PSU but we did try using the old GPU and CPU cables since they matched up.
I'd definitely ask him if he's sure he didn't try this first. Because this is...very bad. Pinouts on modular cables are not universal on the side that connects to the PSU. At no point should mixing cables have been attempted and if it's the first thing he tried, then there's a high chance he simply destroyed a component.
 
Sep 10, 2020
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I'd definitely ask him if he's sure he didn't try this first. Because this is...very bad. Pinouts on modular cables are not universal on the side that connects to the PSU. At no point should mixing cables have been attempted and if it's the first thing he tried, then there's a high chance he simply destroyed a component.
I will ask them exactly what troubleshooting they did before I tried to help in the morning. What would be most likely fried the mobo and the psu?
 

DSzymborski

Polypheme
Moderator
I will ask them exactly what troubleshooting they did before I tried to help in the morning. What would be most likely fried the mobo and the psu?
Depends what the exact pinout differences are in which cable; Corsair ones are out there as there are a lot of aftermarket cables because you see aftermarket versions of these cables, but it's much harder to find a Rosewill one unless you physically have it (I have an old Capstone M around here, but that's not even the same manufacturer making it, unless I'm mistaken).

Theoretically anything connected to a cable that fed the wrong voltage in the wrong place could have been fried, if this is what happened. It's unfortunate that you're not able to be there in person since you'd have likely been able to better report the steps your friend took!
 
Sep 10, 2020
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Depends what the exact pinout differences are in which cable; Corsair ones are out there as there are a lot of aftermarket cables because you see aftermarket versions of these cables, but it's much harder to find a Rosewill one unless you physically have it (I have an old Capstone M around here, but that's not even the same manufacturer making it, unless I'm mistaken).

Theoretically anything connected to a cable that fed the wrong voltage in the wrong place could have been fried, if this is what happened. It's unfortunate that you're not able to be there in person since you'd have likely been able to better report the steps your friend took!
So it turns out the first thing they did is swap the psu unit and used the old cables except for the 24 pin mobo power cable since it was different. So the CPU, GPU, SSD and HDD were all used with old cables. I've advised him to take the drives and gpu to our friends house and see if they work on his system to see if they are fried. He purchased the newegg warranty on his psu so he will trying to get a new unit. He also has a warranty he purchased on the gpu since he had a bad rtx card before.
 

DSzymborski

Polypheme
Moderator
So it turns out the first thing they did is swap the psu unit and used the old cables except for the 24 pin mobo power cable since it was different. So the CPU, GPU, SSD and HDD were all used with old cables. I've advised him to take the drives and gpu to our friends house and see if they work on his system to see if they are fried. He purchased the newegg warranty on his psu so he will trying to get a new unit. He also has a warranty he purchased on the gpu since he had a bad rtx card before.
Oof. Yeah, that was bad. What you suggest is what he needs to do at this point. A giant pain, but now every part essentially needs to be tested in a working machine. That's the first worry for many of us here because too many people try to do that, thinking modular power cables are universal.

Though I honestly would counsel him to be careful and not lie in any of his RMA requests; in the end, it was his action that may have destroyed some parts, not a fault of workmanship from the products, and if he suggests otherwise, I certainly can't endorse an action that consists of criminal fraud.
 

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