Maxpower PL-400EIDGH Active PFC killing primary caps

[goodpsusearch]

Some years ago, I was a newbie here, trying to learn how power supplies work, how to repair them and how to make sure they don't fail again.

It was back then that I got that Maxpower 400W active pfc psu and after finding out it had many bulging caps, including the 2 big 820uF 200V primaries I decided to return it.

3 weeks ago I got an identical Maxpower PL-400EIDGH power supply with the same symptoms.

The fuse was ok, so I checked mosfet, diodes and transistors and found nothing shorted.

Then there was brown glue that I had to scrape from many places, next I reflowed some solder joints that looked bad and then I replaced the bad primary caps with some test capacitors and everything was ready for the AC test.

The psu worked without any problem, the output voltages were quite out of specs but that was expected, as I hadn't replaced the bad output caps yet.

Then I had to test the rectified DC voltage across the primary caps in order to select the appropriate voltage of new capacitors, 220V or 250V.

http://youtu.be/XVFFBqGuUAo

Is this normal for APFC psus or the caps are getting cooked?

Please help me

[stj]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

that's your meter.
it cant track fast changes.

[goodpsusearch]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

The video is taken with psu ON. When running only 5vsb I am able to measure the voltage across primary caps. It's 330V DC.

You say that the meter can't track fast changes. But those changes are normal active pfc operation? They are not going to kill any caps that I put there?

[stj]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

i didnt say that.
the pfc circuit is a pulse generator afaik that tracks the frequency of the mains.
i have no idea what effect it has on the caps.

[japlytic]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

This is a variant of an "old-school" power supply (two high voltage power switchers, TL494/KA7500/IR3M02, two 200/250V primary electrolytics forming an artifical centre-tap which goes to the transformer via a large polyester capacitor), but with active PFC.

[tom66]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

i didnt say that.
the pfc circuit is a pulse generator afaik that tracks the frequency of the mains.
i have no idea what effect it has on the caps.

PFC output voltage is just DC plus an AC component (less than 35% of output voltage) at twice mains frequency, that meter should work fine. I have used ones like that before and had no problem.

I am guessing the PFC circuit has lost its feedback or output voltage sense.

[momaka]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

Picture 12.jpg also shows that the NTC thermistor on the input has a piece blown away from its left side. Might need to replace that too.

As for the APFC - could as well be what tom66 describes. As usual, I suggest gutting the APFC. No need for complexity on an old PSU design like this.

[goodpsusearch]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

It's not possible to remove the APFC in this psu, at least not without reworking the PCB

[lti]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

If you want to repair it, the L4981 datasheet and application notes are here:
http://www.st.com/web/en/catalog/sen.../SC680/PF63215
Click on Design Resources to see the list of application notes. There might be some information there that could help you find the reason why the output voltage is so high. The only places I see where it senses the output voltage are on pins 3 and 14. Pin 3 is used for OVP.

[momaka]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

It's not possible to remove the APFC in this psu, at least not without reworking the PCB

I highly doubt you need to rework the PCB. Should be nothing more than removing a bunch of components and/or jumping through them.

I'm looking at the PCB right now, though it is a bit hard to see traces on the bottom side with all of the glue and burn marks. Looks like there has been a lot of arcing going on. Neet to clean everything well first. Also, once APFC is disabled, remove that resistor on the bottom. Placing power components like that on the bottom side of the PCB without any insulation is a big no-no.

My guess is you will need to do the following to disable the APFC:
- remove the APFC MOSFET (IRFP460)
- remove APFC coil and APFC diode(s) (most likely, these are the 02N60 and D3 - MURxxx).
- remove whole APFC daughter-board.
- Connect positive leg of bridge rectifier to positive side of main cap C5.

Could probably remove a bunch of other stuff too that are related to the PFC, but the above should do it to get the PSU running.

As usual, test with the light bulb trick.

[Behemot]

Re: Maxpower PL-400EIDGH Active PFC killing primary caps

Maxpower having active PFC? Run, run for your life!