Corsair cx600 psu & ASRock B450Pro4 mobo wont start

[Ibod]

HI I have a PC using a Corsair cx600 psu & ASRock B450 Pro4 mother board that won't power on after a shutdown (replaced a dead drive in a raid array) Not the boot drive.

With most things unplugged, including the 24 pin ATX connector, but not the ATX12v to cpu, I have +5.01V on the +5vsb pin 9 from the PSU. When I plug the 24 pin back in to the mobo, the +5vsb fluctuates between 1.1v & 1.9v.

Not sure where to go from here ?

Is the PSU at fault or is the mobo causing the problem

Look forward to any help :-)

If I plug the 24 pin ATX connector into the mobo - with the ATX12v to CPU not plugged in - then I still get +5.01v on the +5vsb at the 24 pin connector
PSU will start up while PS_ON is shorted to Gnd

[JNP-3R]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

It's my understanding that the 5V Standby is often a separate supply in most ATX designs, so it, theoretically, shouldn't care what the rest of the PSU is doing or if the 12V EPS connector is connected or not. The motherboard might be trying to fire up the VRMs though, and if there's a short somewhere that gets turned on when that happens then that could explain what you're seeing.

It's hard to say for sure without more testing (you can always try grounding PS_ON from the backside with the board plugged in and see if the voltage sags or overcurrent kicks in), but if I were a betting person I'd wager it's the MB if all the PSU voltages look okay when ran by itself.

[momaka]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

How old is the PSU? The fluctuating 5VSB could be a bad startup cap in the 5VSB or marginal input bulk cap. Hard to say if that's the issue for sure, though. Can you borrow/get another PSU from another PC and try the motherboard with that instead. Process of elimination with a few spare parts should be able to narrow down the issue down quicker.

[Ibod]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

Hi JNP-3R

Thanks for your reply,

I did try grounding PS_ON with the 24 pin and 12v 8pin cpu plugged in and the +5vsb fluctuates between 1.1v & 1.9v.

[Ibod]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

Hi Momaka,

The Corsair CX600 PSU is over 8 years old, spent at least 4 years in a bit coin mining rig (on 24/7) before I bought it second hand. Then I have used it in a media center also on 24/7.

I have opened it up and found a very very slightly domed Samxon 2200uf 10v GF(M) ZDD 105°C8.
I fairly sure this is the smoothing cap on the 5vsb. + pin connects directly to the purple 5vsb wire - pin goes to transformer terminal.

Can't find these anywhere is there a replacement for these GF(M) series caps ?

[momaka]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

I have opened it up and found a very very slightly domed Samxon 2200uf 10v GF(M) ZDD 105°C8.
I fairly sure this is the smoothing cap on the 5vsb. + pin connects directly to the purple 5vsb wire - pin goes to transformer terminal.

Yup, that will do it.

At this point, you might as well replace all Samxon GF caps in the PSU.

Can't find these anywhere is there a replacement for these GF(M) series caps ?

While Samxon GF aren't the too terribly unreliable (hey, the PSU lasted 8 years, that's not too bad ), they are known to fail after a while. Same with Teapo SC and a number of other "higher tier" Taiwanese capacitors.

If you want a more permanent fix, use high quality Japanese capacitors. Below are listed some manufacturers and the series from them that should work as a replacement for Samxon GF:

Manufacturer................................Series
Nichicon ................................ PW, PA, HE, HD, HV, HW
United Chemicon (UCC) ............ KY, KYA, KYB, KZE, KZH, KZM, LXZ, LZA
Panasonic .............................. FC, FK, FR, FM, FS
Rubycon ................................ YXJ, YXH, YXG, ZL, ZLS, ZLH, ZLJ, ZLK

Note that you do no need to stick to the 10V rating. Being that your Samxon GF cap is on the 5VSB, it sees only a maximum of 5V. So you could also use 6.3V and 16V caps. Just mentioning this, in case you run into availability issues. Slightly higher or lower capacitance won't adversely affect things either (down to 1800 uF or up to 2700 uF is more than likely to be fine.)

Also, consider replacing the big 400V cap on the primary side if you have the budget. After a while, those fail too due to stress from the APFC. 8 years in a mining farm could have taken a toll on it already. Or at the very least, if you have one of those transistor testers that can also measure capacitors, pull the big primary cap out (make sure to discharge it safely first) and check/measure it. Sometimes they either loose capacitance or go high ESR, and that can cause lots of damage to the PSU when they finally fail.

[Ibod]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

Hi Momaka,

Thanks for all that info :-)

I'm going to change the PSU's 5vsb cap and the bulk cap then make sure the Mobo is good.
(see post #3)

Will keep you all updated :-)

[Ibod]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

Hi

Just looked up the Bulk Cap, its a ...

Samxon
270uf
400v
85°c
LP(M)
Dia 25mm
Hight 40mm
Lead spacing 10mm

Can you recommend good series for this Capacitor ?

Assuming the same makes as before are all good.

Thanks

PS Is there somewhere that explains what series caps you should chose ?
Also I assume which make is down to knowledge of what makes are good.

[momaka]

Re: Corsair cx600 psu & ASRock B450Pro4 mobo wont start

Hi

Just looked up the Bulk Cap, its a ...

Samxon
270uf
400v
85°c
LP(M)
Dia 25mm
Hight 40mm
Lead spacing 10mm

Can you recommend good series for this Capacitor ?

Before I do, let me ask you this: is the PCB of the PSU silkscreened / marked for a bigger capacitor? If yes, consider a replacement with both higher capacity and higher voltage rating here. 270 uF for what is supposedly a 600 Watt PSU is really on the low side. The manufacturer really should have used at least 330 uF (or preferably 390 uF), but it's not critical that they do, unless the PSU is used at a high load all the time.
As for the voltage rating... higher-end PSUs always use 420V or 450V caps. 400V is cutting it a bit too close to the boosted APFC voltage (typically 370 to 390V) and over time, that too will "exhaust" a cap quicker.

With that said, let me know what is the maximum diameter and cap height you think your PCB/PSU can accommodate.

For 25 mm diameter and 40 / 42 mm height (I don't imagine an extra 2 mm will break the bank here) and 10 mm LS, here are some caps I found on Digikey:

Nichicon LGN, 420V, 270 uF, MFG P/N: LGNW6271MELA40
https://www.digikey.com/en/products/...MELA40/2540562

United Chemicon LHS, 450V, 270 uF, MFG P/N: ELHS451VSN271MQ40S
https://www.digikey.com/en/products/...1MQ40S/8568225

Nichicon LQS, 420V, 270 uF, MFG P/N: LQSW6271MELA40
https://www.digikey.com/en/products/...MELA40/3930099


If you have an extra 10 mm of height to spare (about 52-53 mm height), there's also these:

Rubycon MXG, 450V, 330 uF, MFG P/N: 450MXG330MEFCSN25X50
https://www.digikey.com/en/products/...N25X50/3565424

Nichicon LGN, 420V, 330 uF, MFG P/N: LGNW6331MELA50
https://www.digikey.com/en/products/...MELA50/2540565

Nichicon LGG, 420V, 390 uF, 25x52 mm, MFG P/N: LGGW6391MELA50
https://www.digikey.com/en/products/...MELA50/2540241

Rubycon MXK, 420V, 390 uF, 25x47 mm, MFG P/N: 420MXK390MEFCSN25X45
https://www.digikey.com/en/products/...N25X45/5023813


On the other hand, if you can't go higher than 43-45 mm but have an extra 5 mm for the diameter (i.e. the PCB can take 30 mm diameter capacitor), then these are an option:

United Chemicon KMQ, 450V, 330 uF, MFG P/N: EKMQ451VSN331MR40S
https://www.digikey.com/en/products/...1MR40S/4001130

United Chemicon LXS, 450V, 330 uF, MFG P/N: ELXS451VSN331MR40S
https://www.digikey.com/en/products/...1MR40S/4001699

Rubycon MXG, 450V, 330 uF, MFG P/N: 450MXG330MEFCSN30X40
https://www.digikey.com/en/products/...N30X40/3565638

Rubycon VXH, 450V, 330 uF, MFG P/N: 450VXH330MEFCSN30X40
https://www.digikey.com/en/products/...N30X40/3565655

Rubycon MXH, 450V, 390 uF, MFG P/N: 450MXH390MEFCSN30X40
https://www.digikey.com/en/products/...N30X40/3565641

Nichicon LQS, 420V, 390 uF, MFG P/N: LQSW6391MELB40
https://www.digikey.com/en/products/...MELB40/3930103


And if you can squeeze both bigger diameter (30 mm) and height (52 mm), again with same 10 mm lead spacing, that opens a few more options:

Nichicon LGN, 450V, 390 uF, 30x52 mm, MFG P/N: LGN2W391MELB50
https://www.digikey.com/en/products/...MELB50/2540511

Panasonic TS-HC, 450V, 390 uF, 30x52 mm, MFG P/N: EET-HC2W391KA
https://www.digikey.com/en/products/...W391KA/1755787

Panasonic TS-HC, 450V, 390 uF, 30x47 mm, MFG P/N: EET-HC2W391DF
https://www.digikey.com/en/products/...2W391DF/816280

Panasonic TS-HC, 450V, 390 uF, 30x47 mm, MFG P/N:
EET-HC2W391KF
https://www.digikey.com/en/products/...W391KF/1755786

I also like to add a polypropylene metal film capacitor in parallel with the main cap (0.1 uF to 2.2 uF @ 450-630V rating) and have noticed many server and high-end PSUs do it as well. It helps take on some of the high-frequency ripple from the main cap. The only issue is, you'd have to find a place to fit it in your PSU. Usually that requires some modifications (i.e. drilling holes in the PCB or finding which components you can solder the cap's leads to), so I don't imagine you'd be willing to try it, at least not as a first PSU repair. BUt just mentioning it here in case anyone else ever finds the info on this PSU and is willing to do this too.

PS Is there somewhere that explains what series caps you should chose ?

I can't remember off top of my head.
But in general, when the circuit involves any kind of high frequency switching or SMPS (switch-mode power supplies), it's better to go with the low ESR series listed above in my previous post.

As to which series to choose specifically...
First find a datasheet of the capacitor you are trying to replace (if you can - some obscure cheap brands may not have one that's easy to find or at all.) Then look up the impedance (we often use this synonymously with ESR... those they are not exactly the same... but close @ ~100 KHz) and ripple current rating of the specific capacitor you have (i.e. find the voltage rating and capacitance of the cap that's to be replaced and then find its impedance and RC in the datasheet.) If an impedance rating does not exist, then that means the capacitor is "general purpose" type. In such case, just look up the RC rating and try to get something within the ballpark of that (though it's usually not critical if you don't.) Same usually applies to impedance / ESR as well - replacement cap specs should be in the "ballpark". I'd say up +/-50% won't cause issues almost any time.

Also I assume which make is down to knowledge of what makes are good.

More or less.

Pretty much the "big 5" Japanese cap manufacturers are the only ones that consistently make good caps. These are Panasonic, Rubycon, Nichicon, United Chemicon (or Nippon Chemicon formerly), and Sanyo (now Suncon.)
They did (and still might) have a few series once in a while that is problematic... but overall, they have been the most consistent for quality electrolytic caps.

From the non-Japanese manufacturers, generally OK brands are Cornell Dubilier (CDE), Epcos / TDK, Illinois Capacitor (also now under Cornell Dubilier, I think) and Mallory. But these generally you won't find to offer low-ESR caps like the Japanese brands listed above. They are usually more suited towards general purpose high-voltage applications and typically come as "large can" caps.

Will keep you all updated :-)

Sounds good!