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Old 02-17-2021, 06:19 PM   #1
Psychedelic
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Default Corsair AX850 low 12v and 5v voltage with random reboots.

Hi guys,

I am having problems with an Corsair AX850 Gold PSU. I have had the PSU FOR around 8 years but it had not been used much. This PSU was used to power two video card and an i7 CPU originally. I noticed that the 12v power was going as low as 11.4v and the 5v was going lower than 5%. I was getting random reboots. I found that the motherboard socket had bent pins and one actually broke. Therefore, I assumed that was the problem and not the PSU. I rebuilt a whole new system. This time AMD. I decided to use this PSU since I had it.

Now with the new system I am still seeing the low voltages under load with a single low power GPU (GTX 1060) under load. I have been doing some reading and watching videos. The information I have gathered and from some people I have spoken to it sounds like an issue with some caps going bad.

I know how to solder and desolder. I am not an expert at it by any means. I do know and understand the risks of opening a PSU. I own a PC repair shop and build and fix PC's. However, I have never got into electronics work soldering etc. I figured if I can do this than I can start salvages some of the more expensive stuff that goes bad. My question is does this sound like caps going bad? I know certain brand caps are better than others. What are some of the good brands to to with? Is there a certain type?Tomorrow I will take it apart and look for bulging and leaking caps. Then report back with what I find.

Thanks,
Rocky
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Old 02-18-2021, 05:23 AM   #2
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Welcome to the forum

I have one question for you what brand of capacitors are on this board

I would recommend replacing the capacitors around the switching power supply regulator and any capacitor under 100uf
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Old 02-18-2021, 08:30 AM   #3
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by sam_sam_sam View Post
Welcome to the forum

I have one question for you what brand of capacitors are on this board

I would recommend replacing the capacitors around the switching power supply regulator and any capacitor under 100uf
I have not got around to taking it apart yet. However, I will be checking it out later today. Would this project be something I can tackle with any soldering iron with temperature control? I am going to order one from Amazon today since I have prime it will be here tomorrow. Like I said I'm new to all this. I have used a Bernzomatic butane soldering iron up until now. However, there is a problem with the ignitor in both the ones I have ��

I did some research and this is the info I was able to obtain without taking it apart. This is from overclockersclub who did a review on this PSU. "The capacitors are a mixture of conventional electrolytic by Nippon Chemi-Con and some solid state capacitors used mainly on the DC-DC converters." The product description for this unit said it uses high quality Japenese capacitors. However, I found people saying unless you get an AXI model you get crappy caps. So I'm confused.

Last edited by Psychedelic; 02-18-2021 at 08:31 AM..
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Old 02-18-2021, 10:34 AM   #4
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Here is some pictures I was able to take of the PSU. I do not see any bulging caps or any that seam to be leaking. Could you please point out the area in which the caps are that I should replace?
Attached Images
File Type: jpg IMG_20210218_112259810.jpg (577.5 KB, 27 views)
File Type: jpg IMG_20210218_112313281.jpg (613.4 KB, 20 views)
File Type: jpg IMG_20210218_112327825.jpg (546.7 KB, 18 views)
File Type: jpg IMG_20210218_112335593.jpg (474.4 KB, 14 views)
File Type: jpg IMG_20210218_112340419.jpg (465.9 KB, 14 views)
File Type: jpg IMG_20210218_112402323.jpg (582.6 KB, 14 views)
File Type: jpg IMG_20210218_112415213.jpg (820.2 KB, 12 views)
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Old 02-18-2021, 12:16 PM   #5
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

It is highly unlikely to be bad capacitors: this range of power supplies uses good capacitor brands.
Have you used a multimeter to measure the 12v voltage or what is the source you know for it being low?
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Old 02-18-2021, 12:24 PM   #6
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by Per Hansson View Post
It is highly unlikely to be bad capacitors: this range of power supplies uses good capacitor brands.
Have you used a multimeter to measure the 12v voltage or what is the source you know for it being low?
There is different programs I have that monitor voltages. They were showing low voltages under load. Therefore, I used a multimeter after that. If it is not caps what the heck could it be? I really do not want to junk it because I paid a good bit for it when I got it. Up until this started happening it was a solid unit.

Oh I forgot to mention. This unit had a problem with the fan header from the factory. It is a very silent unit so you cannot hear when the fan kicks on. It also only kicks on once it hits a certain temp. One time it got real hot and kicked off. I opened it up to see what was going on and the fan header was melted and the fan had not been kicking on. My guess is maybe this is what caused the unit to start acting up. I'm wanted to say it was around the time I started noticing problems. I replaced the fan header and made sure it was working. My guess is maybe this is caused some of the caps to get too hot and made them go bad?

Last edited by Psychedelic; 02-18-2021 at 12:31 PM..
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Old 02-18-2021, 01:05 PM   #7
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

If the unit got hotter than 110°C for a few hours then it is possible.
Why don't you use the warranty claim, these come with a 10 year warranty.
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Old 02-18-2021, 01:49 PM   #8
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by Per Hansson View Post
If the unit got hotter than 110°C for a few hours then it is possible.
Why don't you use the warranty claim, these come with a 10 year warranty.
I believe there are two different version from what I can tell. One is the older variant which I have that is only gold rated which comes with I believe a 7 year warranty that was up last year. The new AX series had a 10 year warranty and is Titanium rated. This is why I am trying to fix it.
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Old 02-19-2021, 07:33 AM   #9
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by Per Hansson View Post
If the unit got hotter than 110°C for a few hours then it is possible.
Why don't you use the warranty claim, these come with a 10 year warranty.
I found someone selling this PSU and all the cables on ebay for $40. He said the PSU will not power on. I wonder if it could be as simple as a bad fuse or something? If I purchased it between the two do you think I could end up with one functional unit?
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Old 02-19-2021, 08:25 AM   #10
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

probably not.

firstly a blown fuse has a murderer! you would need to find the overload.
second - if it does have a bad fuse then your probably looking at a bad main smoothing cap, a pfc diode and one or more dead fets - it's going to get expensive fast!
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Old 02-19-2021, 08:36 AM   #11
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

FFS, I had a 2008 FSP 500 with Ost and Teapo caps last for several years! IIRC, the voltages were still normal in 2016 and there were no visibly bad caps, when I last had it in 2016, before I gave it away along with my FX rig in 2016 to trade for a decent monitor.
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Old 02-19-2021, 08:42 AM   #12
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by stj View Post
probably not.

firstly a blown fuse has a murderer! you would need to find the overload.
second - if it does have a bad fuse then your probably looking at a bad main smoothing cap, a pfc diode and one or more dead fets - it's going to get expensive fast!
Eeeeek okay that's out then. I guess what I will do then is get a new PSU from EVGA. They have a page where they sell bstock PSUs at a discounted price with warranty.

Can capacitors be bad and not show any physical symptoms? Like can they be bad but not bulge or be leaking? If so I was thinking maybe I will buy a kit of capacitors off Amazon as well as a soldering kit. This will give me something to tinker around with and practice at the very least. If I'm lucky maybe after recapping I will be able to get the PSU to function correctly. If not I'm not out much because I actually need a good soldering iron kit. Plus the capacitors will come on handy for other projects.
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Old 02-19-2021, 10:53 AM   #13
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

well yes, caps can dry up internally with no external signs.
and dont trust components from amazon.
as for soldering, psu's are unforgiving - you need a powerfull temperature controlled iron.

something T12 based like these:https://www.youtube.com/watch?v=w0nZCK7B-0U
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Old 02-19-2021, 12:18 PM   #14
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by stj View Post
well yes, caps can dry up internally with no external signs.
and dont trust components from amazon.
as for soldering, psu's are unforgiving - you need a powerfull temperature controlled iron.

something T12 based like these:https://www.youtube.com/watch?v=w0nZCK7B-0U
Awesome thanks for your help. Do you know a reputable place I can get a variety of good caps?
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Old 02-19-2021, 12:19 PM   #15
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

Quote:
Originally Posted by Psychedelic View Post

Can capacitors be bad and not show any physical symptoms? Like can they be bad but not bulge or be leaking?
Yes! Ironically, high-quality caps are more likely to invisibly fail, but that's usually at nearly 45 years old for alarm systems and at least near 20 years old for PCs and that's usually if not powered up. They are more likely to fail without leaking or bulging, when they are sitting for years!
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Old 02-19-2021, 03:12 PM   #16
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

I have good news! I found a cap that was bad. It was a little guy and was hard to see. I fired up my pain in the butt Bernzomatic butane soldering iron which luckily I was able to get enough butane in to get it to fire up and removed it. I found the same cap on another psu I had laying around that I got with a case I bought years ago. I managed to get it out as well as the bad one on the PSU I am working on. Well, I actually had to end up switching to a another soldering iron I just so happened to have laying around that is an electrical one. It was able to get hot enough to get them out. Once out I carefully soldered it into place. It was hard to get it back in due to its location. However, after taking a little break to calm down I came back and managed to get it in. I plugged in the PSU and ran a stress test on the CPU and GPU to put it under a heavy load. I then whipped out the multimeter and tested the voltages. Everything is good to go now 😉 thanks for all your help fellas!
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Old 02-20-2021, 01:46 AM   #17
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

That's really impressive you found the culprit in such a complex PSU!
Did you take any pictures of the capacitor that was bad and its location?
Maybe it could help someone in the future...
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Old 02-20-2021, 06:11 AM   #18
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

it's even more impressive that you did it with a Harbor Freight / CENTEC meter!!
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Old 02-20-2021, 08:22 AM   #19
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

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That's really impressive you found the culprit in such a complex PSU!
Did you take any pictures of the capacitor that was bad and its location?
Maybe it could help someone in the future...
I didn't take any pics but hopefully I can find the little capacitor because the trash didn't go out yet. I did not think to take pictures because you guys are much more knowledge than me. I thought this was like really basic stuff. However, if I can find the cap I will take pics of it and tear down the PSU and show where it was.
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Old 02-20-2021, 08:27 AM   #20
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Default Re: Corsair AX850 low 12v and 5v voltage with random reboots.

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it's even more impressive that you did it with a Harbor Freight / CENTEC meter!!
I just used it to measure the voltage the PSU was putting out under load. I have a really good one but my son used it and left it on. The battery was dead and I couldn't find a 9 volt. So the harbor freight got the job done. I forgot I even had it. It came for free with a precision tool kit I bought 😂😂😂 Anyways I'm just happy I got this fixed. To replace the unit it would of cost almost $300. Granted the new versions are platinum rated instead of gold though.
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