Corsair CX750M under load !

[guizmo1967]

Hi,

I have this power supply, when I check the voltages at each output pins (paperclip method), everything is ok !

When I only plug this PSU to my motherboard, computer start no problem.

When I connect my Gigabyte RTX 2060, computer won't start ??? It must be load related but what could be the problem ?

I'm not a newbie when it comes to electronics, not so much with PSU !!

Thank you !

[RukyCon]

Are you able to take photos of the power supply board? As that could be helpful, and have you tested your rig with a spare power supply just to rule out any issues there causing the power supply to trip (you say that the power supply comes on fine until you connect the GPU to it, so I just want to make sure that's ruled out to prevent this from becoming a wild goose chase)

My first thought would be to check the secondary caps and make sure they're not leaking/are still in spec, I know some older Corsair units used Teapo caps, and that brand is known to be problematic, particularly because they are known to fail without showing any outward signs of failure (though that might only be true for the older G-Luxon(?) Teapos, and not the modern Jammicon ones like your unit may have).

[guizmo1967]

I tested my rig with a EVGA 850 G2 and it is working fine ! The problem is really the Corsair PSU.

Like I said, the Corsair turns on when only the motherboard is plugged and does not when I add my GPU ?

Maybe there is something wrong with the OCP (Over Current Protection) or the power IC ??

I can't find the schematic for the Corsair CX750M anywhere ....

[CapLeaker]

Well, this is a good piece of info. If you stitch it all together, you know the 12V power rail is the problem and the supervisor IC is shutting down the primary for one reason or another.

You CAN add capacitance on the 12V rail and see what it does. You also can try to replace the main filter capacitor, that will also do weird things (read my IPman PSU thread). And you can disable the supervisor IC temporarily if it needs to be.
https://www.tomshardware.com/reviews...su,4799-3.html

Apparently the PSU has a DC to DC power converter for the lower voltage rails… something else to look at. Verify the Supervisor IC WT7502 turning off the primary.

[guizmo1967]

Thanks for the link.

So my understanding is the transcient spikes are the cause for the PSU to not turn on ??

From your link:

"The bulk cap is sourced from Nichicon and its capacity is low for a 750W PSU. As a result, we don't expect the unit's hold-up time to reach 17ms, per the ATX specification's requirement."

Do you think the problem is more on the primary or the secondary side ??

How do I disable the supervisor IC ??

What would you do as the first step, change the bulk capacitor for a bigger one (more capacitance) ??

[redwire]

Have you replaced any of the electrolytic capacitors in this PSU? They all look original lol.
I would first be testing the ones for the 12V rail, they look undersized maybe a couple 2,200uF parts and so much smoke on everything hard to tell what is cooked.

[guizmo1967]

They are indeed all original !

Ok, I'm gonna replace all the capacitors on the secondary side near the 12V rail, but not today, maybe next week.

thank you for your information and your time, I will update this post when I replaced all the capacitors, to see if the problem is fix !!

[stj]

re-cap or dont re-cap, dont half-ass it.
small caps on the primary side used for feedback & startup dont last forever.

[CapLeaker]

Thanks for the link.

So my understanding is the transcient spikes are the cause for the PSU to not turn on ??

From your link:

"The bulk cap is sourced from Nichicon and its capacity is low for a 750W PSU. As a result, we don't expect the unit's hold-up time to reach 17ms, per the ATX specification's requirement."

Do you think the problem is more on the primary or the secondary side ??

How do I disable the supervisor IC ??

What would you do as the first step, change the bulk capacitor for a bigger one (more capacitance) ??

Find my Powerman IP thread tread from 4 years ago. It will explain a bit.
Either the caps on the secondary side or the main filter cap is suspect.

https://www.badcaps.net/forum/troubl...300bn7-2-blown

While you are purchasing new caps for the secondary, just purchase another better one for the primary filter cap too. It won’t hurt.

[guizmo1967]

OK, understood !!

[guizmo1967]

Well I need your opinion once more .....

Parts on Digikey canada with shipping : $62CAD ($20 just for the main filter)

Average price for a Corsair CX750M on Fleebay canada: $70CAD + shipping

Humm, worth it ?? I can't be sure if the problem will be fix !!

[CapLeaker]

Try a different supplier like Mouser, LCSC or TME. Got no junker PSU where you can take the main filter cap off?

[guizmo1967]

I replaced my old Antec TruePower 550 that I had in my PC for almost 12 years (still working fine) with an EVGA SuperNova 850 G2.

The Corsair was given to me with the issue we discussed here. I just want to repair it and keep it as a back up !

So, regarding your suggestion, I looked inside the Antec and the main filter cap has the same specs as the Corsair, 400V 390uF.

Anyway, I was about to give the Antec to a recycling center so I removed the main cap. I'm gonna save $20 !!!

Now time to place my order at Digikey !!

[guizmo1967]

*** UPDATE ***

I have replaced every electrolytic capacitors with Panasonic FR-A. With the same jumper between PS_ON and Ground, the fan is spinning and all voltages are ok !

I installed the PSU in my computer and flipped the switch, the RGB leds on my motherboard were on. Press the power button, the CPU cooler fan spun just a little and stop, computer not starting ....

Before with the old capacitors, my computer was turning on without my GPU, now it's not even turning on when I don't connect my GPU ???

[CapLeaker]

That is because the supervisor IC shut the primary down for one reason or another.

[guizmo1967]

Well $40 in the trash, I took a chance, can't always win ...

I'm gonna removed the main cap and put it back in the donnor PSU. I spent enough time with this PSU, to the recycling center !!

Thank you for your help !

[stj]

dont recycle it - keep it for parts.