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Old 04-06-2021, 07:51 AM   #1
Gold007
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Default Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Hello guys,

I have a problem with this PSU and need your help and knowledge. The unit will not turn on most of the time, but sometimes it does, and then it works fine. +5Vsb is always present, but grounding PS_ON nothing happens. Cycling the power switch (sometimes I can hear a spark pop from the switch) and it will start up after 3-10 cycles randomly, and then all voltages are fine. Remove PS_ON jumper and it won't turn on again until some power cycles. Sometimes it would just turn on for a sec, and then turn off immediately (relay clicks). It is the same as this video shows:
Youtube link

Opened up the unit and I can't see any obvious problems: no bulged caps, no burn or heatmarks, no visible cold joints, nothing. When it turns on nothing seems to be overheating, no smell or smoke. Only the biggest transformer is getting a bit warm, but not hot.

I am quite surprised I can't find any information on this problem, because looking at the market reviews, this whole MWE series has many issues (this one and coil whine) with almost all models. Maybe some of you have encountered this problem, or know what might cause it?

Thanks,
David
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Old 04-06-2021, 08:32 AM   #2
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

it could be a startup cap - good luck finding it.
so if i see this type of intermittent stuff i just replace any cap that is 100uf or less
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Old 04-06-2021, 11:12 AM   #3
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Quote:
Originally Posted by stj View Post
it could be a startup cap - good luck finding it.
so if i see this type of intermittent stuff i just replace any cap that is 100uf or less
Thanks for the tip!
I've tried to replace them (1pc 47uf and 3pcs 100uf electrolytics) but with no luck :/

However I have observed an interesting "habit": When plugged in for the first time after a considerable amount of time (5-10 minutes at least) spent unplugged, it would work perfectly almost every time (turn on and off as supposed to, as many times as I try). But once I unplug it again, the same erratic behaviour again (no turn on at all, or turns on once but no more). Also, I observed that 2 or 3 times when i unplugged (or switched off at the back of unit) it turned on for a moment!
Maybe for someone who is expert in PSUs this is an obvious fault, but for me it just makes less sense...
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Old 04-06-2021, 08:59 PM   #4
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

this is getting to be quite a common fault in pc atx psus nowadays. fyi, the seasonic x-series from many years back started exhibiting this type of issue also. i posted about this before in this forum about the seasonic x-series, so this psu from cooler master certainly isnt the first.

anyway, this type of fault relates to the apfc section. there is some kind of an intermittent fault in the apfc section of the psu. this prevents it from starting correctly and some funky kung fu with the power switch on the back of the psu is needed to get the unit to power on and stay on. what is the voltage printed on the primary cap? 400v?

Last edited by ChaosLegionnaire; 04-06-2021 at 09:01 PM.. Reason: added link.
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Old 04-06-2021, 09:25 PM   #5
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Cooler Master MWE, is on my PSU ban list for potential bad caps and it earned a "meh" rating at Overclockers. com, IIRC.
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Old 04-07-2021, 01:40 AM   #6
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Hmm, so I guess it is not something we can fix easily...

Main cap is 390uF 400V Elite GM series (85C 2000hrs general purpose). When turned on, voltage is around 340V on it.
All other caps are Elite brand too, mostly EY series (105C 4-10000hrs "Low impedance, High ripple current"). From what I have read on forums, Elite is not very high quality, but not total garbage either. I have measured a few of them (with my cheap chinese LCR meter) and all of them seemed quite good, nothing suspicious.
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Old 04-07-2021, 03:44 AM   #7
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

i bet that 400v cap is trashed.
i say that simply because 85' temp rating means it's not a low-esr type.
so the pfc circuit will beat the hell out of it!

a dirty test for marginal caps - heat it up with a hair dryer and see if the unit works when it's hot.

Last edited by stj; 04-07-2021 at 03:45 AM..
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Old 04-08-2021, 01:03 AM   #8
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Quote:
Originally Posted by stj View Post
i bet that 400v cap is trashed.
i say that simply because 85' temp rating means it's not a low-esr type.
so the pfc circuit will beat the hell out of it!

a dirty test for marginal caps - heat it up with a hair dryer and see if the unit works when it's hot.
Okay it is just getting more confusing. I did what you suggested: heated up the main cap to about 70C (guesstimate, I could touch it but it was hot). After that, the PSU works just fine. No matter how many times I switch it off or on at the back, it just works as it should.
I say, okay let it cool down and check again to see if it really is the cap. But no. Since that, the unit works just fine. It's the next day, I have switched it on-off about a hundred times and not once it produced the fault.
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Old 04-08-2021, 04:51 AM   #9
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

the heat spread the liquid that had not dried or crystalized so the cap was more "even"
it still has to go.
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Old 04-09-2021, 04:57 AM   #10
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Quote:
Originally Posted by stj View Post
it still has to go.
It will, don't worry
I just don't know which to choose. I cannot find an exact replacement, these are my options: 330uF 450V 105C Rubycon MXR or Nippon Chemi-Con KMH which are high quality and 450V rated, but slightly lower capacitance than the current 390uF(which is still not much in my opinion). Or I can go with 470uF, but from brands like Jamicon, Samwha or Elite. Jamicon is a no go, Elite is not total garbage afaik (but I am just replacing one, that didn't take the abuse), but I don't know about Samwha. Doesn't sound promising...

Will that 60uF make much difference in load capability? I would rather go with a reputable brand if I am spending money on it.
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Old 04-09-2021, 06:38 AM   #11
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

go for the highest ripple current rating.
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Old 04-10-2021, 11:24 PM   #12
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

Quote:
Originally Posted by Gold007 View Post
Will that 60uF make much difference in load capability? I would rather go with a reputable brand if I am spending money on it.
Not a whole lot, if at all. But probably the hold-up time will suffer even more.
390 uF is already quite a bit too small for a 650 Watt PSU. So going down a bit further just doesn't matter much at this point.

Quality PSUs will typically have around 0.75-1:1 ratio for capacitance:PSU Watts. It's not a scientific formula or anything, but rather my own personal observation. For example, a 650 Watt Dell Lite-On server PSU I opened a long time ago had 2x 330 uF 420V UCC KMM caps inside (so total 660 uF capacitance.) I've also seen some really expensive old SilverStone units with 10 year warranty that had a similar arrangement for the primary caps.

Quote:
Originally Posted by Gold007 View Post
I just don't know which to choose. I cannot find an exact replacement, these are my options: 330uF 450V 105C Rubycon MXR or Nippon Chemi-Con KMH which are high quality and 450V rated, but slightly lower capacitance than the current 390uF(which is still not much in my opinion).
Both of these will probably work fine. Like stj suggested, go for the cap with higher ripple current at 10 KHz (or whatever other high frequency is listed.) If these caps show RC for only 120 Hz, it would be hard to say which has better RC at high frequency, because some GP caps have really good RC for 120 Hz but not so much at higher frequency.

That said, perhaps drop the voltage rating slightly to 420V (yes, 420V caps do exist ) and see if you can find slightly larger capacity then. That may ultimately be the best compromise between capacitance and voltage when there are space limitations. I personally don't recommend going down with 400V caps on an APFC circuit. Seems like even the good Japanese brands will blow/go bad then.

And yeah, don't bother buying any of the non-Japanese brands like Jamicon, Elite, SamWha, and etc. Even though these are actually far from bad brands, they aren't that good either.

Last edited by momaka; 04-10-2021 at 11:28 PM..
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Old 04-12-2021, 03:49 PM   #13
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Default Re: Cooler Master MWE Gold 650W (MPY-6501-AFAAG) randomly won't turn on

In addition to the "usual suspects" - the 'cons plus Panasonic - also consider Hitachi, which has a substantial presence in the 400V and higher marketplace.
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