Corsair RM1000e - Help identify 5VSB Zener diode

[c1q3]

I'm glad that you fixed it. It was pleasure to trying to solve this puzzle even if I lack of experience but there are lots of experts that approved my thought.

[CapLeaker]

Great to hear you got your PSU fixed. Also congratulate yourself for sticking with it. I am sure this thread taught you a few things from different folks on how it works, what to do and learned a few things along the way. Remember the PFC in a PSU needs to work 100% first .

[hobostove]

It's alive under load! I couldn't have done it without all of you, I learned a lot from this little detour. I feel a lot more confident approaching power supplies now. Big thanks to прямо, Per Hansson, CapLeaker, and special thanks to c1q3 for getting the ball rolling in the beginning. Sorry trash can, but you're going hungry today! 😉

Just a quick recap of everything it took:
TNY284 chip for 5VSB
Fusible resistor
15V Zener diode
2 transistors
CM6500UN PFC chip

all because someone dropped a screw in the case.....

[hobostove]

It was my crappy tester again, loose connection. I think it's time to retire it. 12V is present after all! Next step now is to load it and see what happens 🤞

[Per Hansson]

Anyone have some guidance on where to start tracking down why 12V is missing? I have 5V and 3.3V

https://hwbusters.com/psus/corsair-r...-psu-review/3/

The PCB is small and densely populated. To save space, HEC used two vertical boards, one hosting the DC-DC converters that generate the minor rails and one with the FETs that regulate the 12V rail. The heatsinks are large enough to meet the unit's thermal needs without using excessive active cooling, hence keeping noise output low.

The 12V board is right next to the main transformer to minimize energy losses. The platform's design is the typical one: a half-bridge topology on the primary side and an LLC resonant converter. The secondary uses a synchronous rectification scheme for the 12V rail, which feeds a pair of VRMs for the generation of the minor rails

^^That would be a good start

[hobostove]

Anyone have some guidance on where to start tracking down why 12V is missing? I have 5V and 3.3V

[hobostove]

Alright, new PFC chip arrived. Put it in, and now seeing 375 on the main cap. Tester stays on steady now, but no 12V yet. More to do!

[CapLeaker]

O.k.! Time will tell!

[hobostove]

Looks like that resistor was in series with VCC going to the PFC IC. PFC IC is shorted. VCC pin is 3ohms to ground with the chip off the board. 5VSB is back with the chip off. Going to order one. I'll be back in a week

[CapLeaker]

Hmm… how can a resistor change kill the 5VSB?

[hobostove]

Found an open resistor near the PFC IC, has a hole in it. Replaced it and now 5VSB is shorted again. Getting there!

[CapLeaker]

Yeah… no. Your PFC isn't working. You need to fix that first. When the MOSFET shorted all 3 pins, it dumped full power to the gate drive circuit all the way back to the PFC IC. You have to inspect ever single part. Obviously your PFC IC doesn't do anything… depending where you got your parts from could be fake or fluke DOA. Look at the data sheet of the PFC control IC and compare your measurements on all pins. Could be the PFC IC is in under voltage lock out or VCC is missing, a component near by open, a busted trace or something. But if it’s the original PFC IC replace it.

[hobostove]

PFC OUT signal looks like this on the scope, pretty much nothing

[hobostove]

The transistor that was shorted was Q3 on this typical application schematic for the PFC IC (CM6500UN). I replaced it last week and the short is gone. Maybe the PFC chip is dead?

Worth noting the schematic here shows one mosfet, this psu has two. Also, I'm missing the 10ohm resistor and diode between the transistors and the mosfet gate. I do have the 10ohm leading back to PFC OUT though.

https://www.kediman.com/attaches/2017/04/906-vempt0.pdf

[hobostove]

Both led pins of that optocoupler are indeed high. I think I follow now. If the supervisor IC is happy, it'll open a ground path for that led. If it's unhappy, it'll disconnect itself and the gnd side of the LED is normally pulled up somewhere.

I get 167V on the main cap, so next step is try to work out what's wrong with the PFC I suppose.

Going back a bit, before I got 5VSB to come up, I had to solve a short. Looking at it now, it was a transistor headed into the little PFC daughterboard. Probably more than coincidence. I'm looking at that area now.

[CapLeaker]

From what I see, I would expect the supervisor to shut the primary down.
Follow the trace from the FPOB pin. You’ll end up on an optoisolator. Measure each of the 2 pins on the optoisolator on the secondary side against secondary GND. If both pins are at 5V the little led built inside the opto cannot light up, shutting the primary side down.
You can however disable that supervisor IC and force the PSU to stay on by grounding out the FPOB pin.
What’s the VDC on the main filter capacitor when you plug the PSU in and turn it on? If you get only 167VDC your Power Factor Correction circuit isn’t working in the primary. You should have something around to 380VDC. If you don’t get that voltage on the main filter capacitor, no wonder the supervisor IC is shutting things down. No PFC means there will be no high power on the secondary.

[hobostove]

Does your PFC work? At 167VDC at the main filter cap doesn’t seem to be the case.
If you want to know if the supervisor IC WT7527 is shutting things down, measure the FPOB pin. If it latches high, the protection is on.

FPOB is high @ 5V. Datasheet says it's an open drain. Shouldn't it go low if the protection is tripped?

[hobostove]

10.2V then it shuts down

12V


5V


3.3V

[CapLeaker]

Does your PFC work? At 167VDC at the main filter cap doesn’t seem to be the case.
If you want to know if the supervisor IC WT7527 is shutting things down, measure the FPOB pin. If it latches high, the protection is on.

[hobostove]

It might not work without a load: connect something you don't care about, some old hard drives for example or a couple 12v car light bulbs to 12v and 5v outputs.

I attached a load (3 old 3.5" drives), and now it's shutting down immediately and staying dead until it's left unplugged for a few minutes.

That's the protection mode kicking in, because 10.8V for 12V rails is an under voltage condition.

So definitely seems like protection mode kicking in. Maybe without a load 10.8V was just near the threshold of an undervolt condition, and with the load it droops into a definite protect.

Datasheet seems to agree.

Would be the slowest acting “protection mode” in the world. I haven't seen any protection mode that is that slow. I wonder what kind of voltages the op gets on the main filter cap?
I think the supervisor is a WT7527rt. It shuts the PSU down less than a half of a second.

I'm seeing 167V on the main cap. 120V mains here.

So 12V is low and it's shutting down. Where to go from here?