Cooler Master 1200W SPG - No power.

[joystik]

Hi.
Im trying to repair this power supply that went bad over two years ago and was used in a bitcoin mining rig, connected in parallel with a 750w thermaltake psu.(They were running 6 R9-280X AMD Graphics cards)

The board had black marks in the 24 pin connector. However, only the 1200w psu was damaged. It was sent to repair, since i had no experience in psu repair.

Main switchers replaced and it ran for a couple months until it failed again. It now attempts to start but shuts down immediately.

This time, I want to repair it it myself. I have a background in electronics, but I have been working in IT for 10 years now, so my knowledge is a bit rusty and outdated.

I have tested the PFC Mosfets, the main switchers, diodes, secondary rectifier mosfets, capacitors and appear to be fine.

you can see the PSU description in this link

I must be overlooking something. I have desoldered and tested almost every component on the main board.

This unit has a controller daughter board, and i suspect the problem to be there, but I dont know how to test the ICs. Like I said, I have no experience in repairing smps units.

Any input is greatly appreciated, as this effort is more for the learning than anything. I actually will have no use for the psu once its working(if it does).

[stj]

Re: Cooler Master 1200W SPG - No power.

need pictures

[joystik]

Re: Cooler Master 1200W SPG - No power.

I provided a link to a review which has good pictures of the psu.

If you want I could upload pics, just point me to what components u need pictures of. Ill gladly do.

[stj]

Re: Cooler Master 1200W SPG - No power.

no, pictures of the faulty one

[CapLeaker]

Re: Cooler Master 1200W SPG - No power.

Do all secondary voltages come up and then disappear or nothing at all? Does the PFC circuit work (380V DC main filter cap)?

[joystik]

Re: Cooler Master 1200W SPG - No power.

Ok, here are the pictures.

If you need anything specific, just ask.

"Do all secondary voltages come up and then disappear or nothing at all? Does the PFC circuit work (380V DC main filter cap)? "

Only 5v SB. The 12V is missing. Other voltages are derived from the the 12v rail via vrms.

On the primary side, PFC 380V is present. Filter caps charge to 170V.

[stj]

Re: Cooler Master 1200W SPG - No power.

so what caused the bad corrosion, did a large cap leak???

[PeteS in CA]

Re: Cooler Master 1200W SPG - No power.

Is your PFC voltage 340-390V? Or is it 170V? Your +5VSB is a wide range regulator, so it will work at 170V, but 170V would probably cause whatever UV protection the PSU has to keep the output inverter shut down.

If your PFC O/P voltage is 340-390V, some other fault is keeping your output inverter shut down.

If your PFC O/P voltage is 170V, your PFC circuit is not working.

[joystik]

Re: Cooler Master 1200W SPG - No power.

so what caused the bad corrosion, did a large cap leak???

Corrosion do to dusty and humid coastal environment.

[joystik]

Re: Cooler Master 1200W SPG - No power.

Is your PFC voltage 340-390V? Or is it 170V? Your +5VSB is a wide range regulator, so it will work at 170V, but 170V would probably cause whatever UV protection the PSU has to keep the output inverter shut down.

If your PFC O/P voltage is 340-390V, some other fault is keeping your output inverter shut down.

If your PFC O/P voltage is 170V, your PFC circuit is not working.

Ok, this is what I measured.

Input 118V AC

Full bridge rectifier output 165-170V

Rectifier Caps voltage 165-170V

PFC Transistors DS Voltage: 165V (PSU off) 28-30V (PSU On)

Main Switchers. One is on, the other is off. No gate voltage. These drive the main converter.

No secondary output at all, at least cant measure any with my multimeter. Dont have an O-Scope. Only 5V SB, which is present always.

There is a spot between the 2 .39ohm resistors and a big diode, where voltage is 250V. Dont have a schematic of it, Im not sure what connects to it. Ill look into it.

Tested all the transistors and didnt find any faults.

[CapLeaker]

Re: Cooler Master 1200W SPG - No power.

Look at the PFC controller and see if it is actually getting turned on when you force the PSU on. There isn't anything main component shorted at the primary, otherwise the fuse would be blown. That leaves you a few possibilities: One: there is an open, Two the PFC isn't working, third startup cap dried out. Since the Mosfets had been replaced at one point, take a hard look at the PFC itself and the gate drive circuit to these Mosfets.

[joystik]

Re: Cooler Master 1200W SPG - No power.

Look at the PFC controller and see if it is actually getting turned on when you force the PSU on. There isn't anything main component shorted at the primary, otherwise the fuse would be blown. That leaves you a few possibilities: One: there is an open, Two the PFC isn't working, third startup cap dried out. Since the Mosfets had been replaced at one point, take a hard look at the PFC itself and the gate drive circuit to these Mosfets.

Can you spot the third startup cap in the pictures?
Im not sure which one it is.

[joystik]

Re: Cooler Master 1200W SPG - No power.

Managed to replace the PCF chip (CM6802), however not exact match. Got the DIP16 version, not the SOP16, which I am still looking for.

Now the supply tries to start, coils whine for an instant and then shuts down.

Same behaviour every time.