[SOLVED] Touched 12V off 5V line while installing custom LED power switch

Oct 25, 2021
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Hello there, I made a very costly error and accept I am an idiot for doing so. I should have disconnected the power before trying to do anything with my custom power switch/cables. I'm just trying to gauge the extent of the damage and would appreciate any guidance in diagnosing as much of the damage before replacing parts or bringing it to be repaired.
So I just had POWER + to POWER - through a momentary NO switch.
12V over SATA direct from PSU (Corsair RM850x).
Upon adding another switch for a separate unit to my external panel, the pc power switch was in the way. In undoing the terminals, I presume (didn't see it) I touched the 12V line to the 5V line because the PC booted but then died. I cut the power within 5 seconds as I knew I effed up.

Troubleshooting:
Reconnected the cables to my case's power button as normal.
Upon first retry, the PC didn't boot. No lights on MOBO (gigabyte Z390UD), no beeps but I cut the power quick because I could hear something rising, as in, a seemingly increasing power consumption. Reconfirmed all cables etc were in correctly. Tried again, no luck.
No burning smells.
Inspected motherboard and parts and there doesn't appear to be any discolouring, misalignment or any visual problems.
I visually inspected the PSU from outside the casing and there doesn't appear to be any discoloured components, caps or fuses etc with damage appearance.
Following that, I disconnected all power cables from the PSU, leaving just the 24 pin ATX. I jumped pin 4 & 5 and the PSU fan spins. PSU seems good.
I don't want to reconnect the MOBO for fear of doing more damage. I'm praying I didn't fry multiple components!

If anyone thinks I should just go straight to the repair shop then I'm happy to do that. I have a multimeter so I'm willing to try a bit of further diagnosis but I have no experience in doing so. That being said, I did build the PC myself and I don't feel nervous handling computer parts if that makes any difference.

Thanks for taking the time to read my issue
 

jay32267

Champion
I am not surprised the PSU seemed to have survived. They can be pretty tough.

If you want to see if you have 5V at the power switch....I would have the CPU installed. I'm not sure if it's required....buy why not.

I would suspect.....if anything is damaged.....it would be the motherboard.

...but as I said...I'm not clear what you did...but if the motherboard was connected to the PSU....when you did what you did....I think it's very possible the MB got damaged.
 
Reactions: SirShortFuse
Oct 25, 2021
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hmm power switch is running on 5vsb, if u sent 12v there, probably mainboard 5vsb circuit is dead now
check that with multimeter if 5v is there from mobo (power button front panel pins)
Thanks for the response. I disconnected all but CPU from MOBO, is that sufficient for this test? And I have two multimeters actually so should I also check another point simultaneously?
 

jay32267

Champion
"I jumped pin 4 & 5 and the PSU fan spins. PSU seems good. "
You can use the meter to check the PSU voltages at this point.

I would sniff around the motherboard again for anything burnt.

I would suspect the motherboard at this point.

However....I'm not completely understanding what exactly you shorted.
 
Reactions: SirShortFuse
Oct 25, 2021
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"I jumped pin 4 & 5 and the PSU fan spins. PSU seems good. "
You can use the meter to check the PSU voltages at this point.

I would sniff around the motherboard again for anything burnt.

I would suspect the motherboard at this point.

However....I'm not completely understanding what exactly you shorted.
Hi Jay, thank you for taking the time to assess my problem.
I probed all pins following pinouts here: https://pc-mods.com/blogs/psu-pinout-repository/corsair-psu-type-4-cables-pinout and all are fine. The PSU so far seems to have held up.
Is the next step to test the 5V rail like previously advised by kerberos_20 and is this possible without connecting anything or do I need at least the CPU?
 
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jay32267

Champion
I am not surprised the PSU seemed to have survived. They can be pretty tough.

If you want to see if you have 5V at the power switch....I would have the CPU installed. I'm not sure if it's required....buy why not.

I would suspect.....if anything is damaged.....it would be the motherboard.

...but as I said...I'm not clear what you did...but if the motherboard was connected to the PSU....when you did what you did....I think it's very possible the MB got damaged.
 
Reactions: SirShortFuse
Oct 25, 2021
8
0
10
0
I am not surprised the PSU seemed to have survived. They can be pretty tough.

If you want to see if you have 5V at the power switch....I would have the CPU installed. I'm not sure if it's required....buy why not.

I would suspect.....if anything is damaged.....it would be the motherboard.

...but as I said...I'm not clear what you did...but if the motherboard was connected to the PSU....when you did what you did....I think it's very possible the MB got damaged.
Yes you were right from the start. I'm at least accepting the MOBO is toast after doing the PSU probing. My whole PC was connected as usual when it happened so it could be catastophic damage. On an IC level, I essentially plugged an American appliance into an EU outlet. That being said, it's highly unlikely some protection didn't kick in and I'm presuming the cost of the repair will be far less than the cost of a whole new machine.
I'll get testing shortly after dinner
 

jay32267

Champion
There most likely is no protection to protect the MB in this case......if the MB did fail.

However the cost of a MB is going to be much less than a whole new machine.

I don't think you need to go that far (new machine).
 
Oct 25, 2021
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There most likely is no protection to protect the MB in this case......if the MB did fail.

However the cost of a MB is going to be much less than a whole new machine.

I don't think you need to go that far (new machine).
Oh I meant that it would have given way and in the process protects other parts. Anyways I tested the 5 volt POWER + to - without jumping obviously and I got voltages which peaked at 0.55V and then dropped to 0.43V before going a bit erratic around the latter number. Certainly doesn't seem right. Should I not even try to jump the power cables and toss it?
EDIT: power pins rather than cables
 
Last edited:

jay32267

Champion
"voltages which peaked at 0.55V and then dropped to 0.43V before going a bit erratic around the latter number. "

I would think you should have 5 volts here and if you don't I would suspect the MB.

I'm guessing that if you jump Power+ to Power - nothing will happen.
 
Oct 25, 2021
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"voltages which peaked at 0.55V and then dropped to 0.43V before going a bit erratic around the latter number. "

I would think you should have 5 volts here and if you don't I would suspect the MB.

I'm guessing that if you jump Power+ to Power - nothing will happen.
Ok, I think I'll leave it at that as far as testing goes. What do you recommend: buy another of the same MOBO and if that doesn't work bring to repair shop? My thinking is at the very least I'd have a way of ruling out more problems and wouldn't have the added cost of them telling me what I just found out
 
Oct 25, 2021
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Bought a new motherboard and thankfully it's all back up and running. Voltages and temps are stable on CPU-Z and NZXT CAM.
Costly mistake but I learned a lot in the process. Much appreciated for the help guys, saved me a lot of time and money!
 

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