Dps-240fb

[rtstorm]

Re: Dps-240fb

i check purple(+) and black (-) = 0V,
voltage rating if big capacitor is 450V on label

[ben7]

Re: Dps-240fb

I try it and it is OK, no light turn ON. I try without dim bulb, and it is OK. I try to connect green + black but PS did not turn ON. I check big capacitor and it has 328V DC.

Is there 5 volts on the 5v standby wire?

what is the voltge rating of the big capacitor?

[rtstorm]

Re: Dps-240fb

I try it and it is OK, no light turn ON. I try without dim bulb, and it is OK. I try to connect green + black but PS did not turn ON. I check big capacitor and it has 328V DC.

[rtstorm]

Re: Dps-240fb

Ok, i will try when i get back home from work. I will try with old UCC chip and dim bulb.

[ben7]

Re: Dps-240fb

I found some 2.2nF SMD cap, but it is 50V, can i replace it with one that is crumbling?

Nooo, it needs to be atleast 350v.

I dont think you need to replace it, it is just used for filtering, being connected right under that bridge rectifier. I highly doubt there will be any problems with it removed.

[rtstorm]

Re: Dps-240fb

I found some 2.2nF SMD cap, but it is 50V, can i replace it with one that is crumbling?

[rtstorm]

Re: Dps-240fb

Ok, i will try with that. Measure voltage on big cap and post, tofay i will buy the ucc3818 in case i would need to replace

[ben7]

Re: Dps-240fb

Careful here. When the PFC MOSFET shorts, it will backfeed rectified line voltage to its driver, which happens to be inside the UC3818.

Take a look here:

i try to remove 20N60, and bulb did not light up. Then i found some little piece of soldering on board, i think that make the trouble. i remove it and bulb light just for sec and then go OFF. I put back 20N60, and still bulb did not turn ON. But i see some sparks on this capacitor in the picture. The sparks are very small. I remove him and he was 1.56nF. And below capacitor i found some burned areas.

That leads me to think the shorted smd capacitor caused the fuse to pop.
The MLCC capacitors are easily damaged, which probably happened when the supply was taken apart.

As for the dark spot, it could also be from that array of resistors on the bottom of the board.

Of course, yes, the PFC controller chip could still be damaged, but using the lightbulb test and measuring the voltage on the big capacitor will tell us if it is working or not.

[kaboom]

Re: Dps-240fb

The PFC chip is likely not bad

Careful here. When the PFC MOSFET shorts, it will backfeed rectified line voltage to its driver, which happens to be inside the UC3818.


As to the discolored area near C16 on the riser: this is right behind the PFC inductor on the PS main board. As usual, such inductors are undersized (both copper and core) and run hot. They sometimes develop shorted turns, which destroys the PFC MOSFET.

Or, the PFC output cap (330-820u, 350-450V) gets high ESR or opens. Now, the energy stored in the PFC inductor has no place to go. The boosted B+ voltage rises when the PFC MOSFET shuts off (dI/dT) and keeps rising, until the PFC MOSFET, and sometimes diode, are destroyed. At this point the line fuse is blown, the gate driver has been backfed, and NTC (if present) is cracked. If unit is overfused, the line rectifier can short, too. This can all happen before the SMPS PWM even starts!

I stand firmly by what I said on this forum a few years ago- that these PFC boosters were shoe-horned in, like a lousy afterthought. "Just make 'em with PFC, who cares about the horrible efficiency."

[ben7]

Re: Dps-240fb

By the "rest" you mean the other capacitor? Or i coud leave the other capacitor.

Well, you said it was crumbling, so that could still cause a short if the rest isn't removed.

[rtstorm]

Re: Dps-240fb

By the "rest" you mean the other capacitor? Or i coud leave the other capacitor.

[ben7]

Re: Dps-240fb

ok, i will replace it tomorrow.
please tell me if I can replace the capacitor that i mentioned that sparkles with an ordinary electrolytic or really needs to be that little capacitor. (this one is crumbling)

Actually, just remove the rest of that small capacitor, and do the lamp test.
The little capacitor there is just for filtering, there should not be any noticeable difference with it removed. If the lamp test passes (lamp glows only briefly), then try it without the bulb.

The PFC chip is likely not bad, that capacitor got stressed and shorted out.

[rtstorm]

Re: Dps-240fb

ok, i will replace it tomorrow.
please tell me if I can replace the capacitor that i mentioned that sparkles with an ordinary electrolytic or really needs to be that little capacitor. (this one is crumbling)

[ben7]

Re: Dps-240fb

i think this is the controller,

Yes, replace IC401, and do the lightbulb test again.

[rtstorm]

Re: Dps-240fb

i think this is the controller,

[ben7]

Re: Dps-240fb

Huh? Doesn't look burned at all. They just omitted a capacitor there. The solder shows no sign of anything being there as far as I can tell.

[rtstorm]

Re: Dps-240fb

This is burned area,

[ben7]

Re: Dps-240fb

i try to remove 20N60, and bulb did not light up.is the 20N60 gone bad, or something trigger it to be open all the time?

The controller for it is shorted. The PFC controller is likely on the riser board, like kaboom said. I dont know why I thought the UC3845 was for the PFC

[rtstorm]

Re: Dps-240fb

i try to remove 20N60, and bulb did not light up. Then i found some little piece of soldering on board, i think that make the trouble. i remove it and bulb light just for sec and then go OFF. I put back 20N60, and still bulb did not turn ON. But i see some sparks on this capacitor in the picture. The sparks are very small. I remove him and he was 1.56nF. And below capacitor i found some burned areas.

[kaboom]

Re: Dps-240fb

i replace 0.22 resistor and UC3845. Connect over dimbulb and bulb turn ON.

You've got more parts to replace. The 3845 is for the SMPS, not the PFC-booster. The PFC controller is likely on the riser.

That 20N60 stays on and shorts the DC side of the line rectifier because its gate driver blew when the original 20N60 blew.

Remove the 20N60, and apply power with the dim bulb. The big cap should now charge up. If the bulb still lights up, remove Q1 and try again.

You can leave that heatsink out and apply power. If the bulb lights up now, the line rectifier's shorted.

But i did some idiot thing, i connect the power when 20N60C3 was not solder (just plug into PCB).

Don't be "in a hurry," or any of that stuff. You'll only get mad, and end up fixing nothing!