Power Man ip-p300bn7-2 blown

[CapLeaker]

Today the victim is a Power Man ip-p300bn7-2. It's a small size PSU. Problem was it's totally dead, no 5VSB or PSon. Open it up and the TNY277 played a game of jack in a box. Besides the blown TNY277, I cannot find any short or opens on hot or cold side. No problem of changing the TNY277 and voila, 5VSB is solid and PSon returned.

Now the fun begins:
Pull PSon to GND and the power supply starts for a split second and turns back off. The supervisor IC is a WT7525-140 and the PFC IC is a FAN48001N in this darned thing. I measured all the power rails on start up, which come up for a split second. Had the diodes out and checked properly for shorts / opens and nothing. I get proper power to the supervisor IC. Measured pin 3 FPOB and it stays at 4.7V?

Checked the PFC circuit and measured the main filter cap going from ~ 170V to about 310V before it shut off, measured with Min/Max on my DMM. So I thought the FAN48001N and the Mosfet are working. Had the PFC fet out and nothing. I did notice that there was a black carbon trace from the TNY277 over to the board with the FAN48001N, but I cleaned that all up.

It's Sunday morning and I am tired. But WTF am I missing? Does anyone have a schematic for this thing? With the PFC starting to boost and the supervisor detecting a fault with FPOB latched high, what's going on here if all my power rails are starting to come up? Is my supervisor IC bad?

Almost thinking I am loosing my magic? Damn!

Edit: the 12V rail measures 12.9V on the min/max on my DMM... over volt protection kicking in?

[sam_sam_sam]

Originally Posted by CapLeaker

Today the victim is a Power Man ip-p300bn7-2. It's a small size PSU. Problem was it's totally dead, no 5VSB or PSon. Open it up and the TNY277 played a game of jack in a box. Besides the blown TNY277, I cannot find any short or opens on hot or cold side. No problem of changing the TNY277 and voila, 5VSB is solid and PSon returned.

Now the fun begins:
Pull PSon to GND and the power supply starts for a split second and turns back off. The supervisor IC is a WT7525-140 and the PFC IC is a FAN48001N in this darned thing. I measured all the power rails on start up, which come up for a split second. Had the diodes out and checked properly for shorts / opens and nothing. I get proper power to the supervisor IC. Measured pin 3 FPOB and it stays at 4.7V?

Checked the PFC circuit and measured the main filter cap going from ~ 170V to about 310V before it shut off, measured with Min/Max on my DMM. So I thought the FAN48001N and the Mosfet are working. Had the PFC fet out and nothing. I did notice that there was a black carbon trace from the TNY277 over to the board with the FAN48001N, but I cleaned that all up.

It's Sunday morning and I am tired. But WTF am I missing? Does anyone have a schematic for this thing? With the PFC starting to boost and the supervisor detecting a fault with FPOB latched high, what's going on here if all my power rails are starting to come up? Is my supervisor IC bad?

Almost thinking I am loosing my magic? Damn!

Edit: the 12V rail measures 12.9V on the min/max on my DMM... over volt protection kicking in?

Hang in there ⬆️

I hope that you figure out what going on with this switching power supply I am going to follow this post to see if you found out what the issue is

[CapLeaker]

Well... I am hanging all right I guess. So I fiddled around a bit more.
Turns out the opto in question is the middle one. Both pins go back to the WT7525. Pin 2 of the opto goes to the FPOB pin 3 on the supervisor. Pin 1 of the opto goes through a 1k resistor, through a small diode to pin 13 VCC on the WT.
Problem is there is not enough voltage difference for the opto to turn on.

O.k., so PSon, PSU starts, the supervisor isn't turning the opto on, so the PFC shuts down. Baaaaaaaaaaaaah. On the opto between GND and pin 1 = 5V. Between GND and Pin 2 I get 4.4V... sooo at 0.7V difference on the opto pin 1 and 2 isn't enough to turn the forker on.

Problem is, I don't have a supervisor IC that I could try. And I don't have another working one of these to see what voltages are normal around the WT7525. Aarrgh!

[sam_sam_sam]

It looks like you can find them on EBay and it looks like it is a Chinese made part “ WT7525 ”

Here is the data sheet for this part number

https://www.radioradar.net/en/files.html?fid=687937

[CapLeaker]

Thanks sam! I did already look at the data sheets. I also looked at some other power man ip PSU schematics. Some only use 5VSB, others 12v and 5VSB using some Weltrend supervisor for FPOB and the optocouplers. If the 12v rail is supposed to kick in that optocoupler via a diode, it doesn’t. If it’s only the 5VSB on the optocoupler well, the FPOB pin doesn’t pull low. So what gives?

[sam_sam_sam]

I am confused about what the recommended voltage for the input voltage that are suppose to be monitoring because it does not tell you what the recommend voltage because there is NO information on the data sheet what is this crap ( it only gives you the maximum values ) I have looked at other data sheet for this type of other supervisor ic chip that gives you this information

[CapLeaker]

Meanwhile I did more tracing and my PSU uses only the 5VSB going to the optocoupler back to the supervisor IC pin 3. Found a cracked solder joint on the daughter board, resoldered it, but still same problem.
So if the FPOB latches “high” the supervisor IC has either sensed a fault or is faulty. With 5VSB on one side of the optocoupler and FPOB pin on the supervisor latched high, there is only a 0.6V or so difference. That’s not enough for the optocoupler to turn on the PFC.
I know it’s not a missing voltage on any of the rails. The only thing I didn’t do is taking the TL431a’s out and check them…
Right about now I’d be very thankful for some similar PSU schematics using a WT7525 and a FAN48001N.

[CapLeaker]

Went for another goose chase this evening. Took the TL431a (sine I saw a little heat on it) and a SB560 out to see if there is something not quite right… no go. Same story.
Not so sure how well the WT7525 is constructed, but maybe it got a bit too much power, when the TNY277 blew. I am going to rule out the PWM for the PFC, since it is trying to boost voltage. If there would be a anything wrong with that PFC, it wouldn’t boost Voltage at all.

[CapLeaker]

Looking at the WT7525 datasheet, I got the idea and jumped pin 2 GND to pin 3 FPOB, trying to force it on and hopefully firing that PSU up. Plugged it in aaand? No
The PSU fired right up! Well, that's a step in the right direction! Anyway... All voltage rails came up, but none of them are stable swinging back and forth about ~ 0.5V. The voltage on the main filter cap also isn't quite stable and is going between 370V ~ 375V.
5VSB is rock solid. While most voltage rails are a bit under voltage what they supposed to have, the 12V rail is swinging to 13.1V at times.

Question now is: Why is this POS not regulating properly?

[CapLeaker]

Aaand? It's fixed!

Getting old is for the shits. When I forced the PSU on I had nice piece of quietness in my house and heard the PFC ringing in my current limiting light bulb trick. The light bulb made a funny continuous sound as soon when the PSU was running. Now why would it do that?

Answer: The Teapo LH series 400V 180uF main filter capacitor had a value of 5.466 nF with an ESR of 9.2 kOhms! I never checked it with my ESR meter, just measured volts from it. Physically the cap looks like brand new. You can't tell the difference! Replaced the main filter capacitor and all problems went away.

Anyway, the PSU is working A1... another one saved. As soon as I heard that PFC in the light bulb, I knew I was barking at the wrong tree.

[PeteS in CA]

Putting together anecdotal comments I’ve seen around here, I wonder if a lot of the snap-in type caps, which were originally designed for 50/60 Hz usage, are not suitable for the high frequency filtering for active PFC.

[CapLeaker]

Originally Posted by PeteS in CA

Putting together anecdotal comments I’ve seen around here, I wonder if a lot of the snap-in type caps, which were originally designed for 50/60 Hz usage, are not suitable for the high frequency filtering for active PFC.

Funny you mentioned it and you may be on to something... I just went on Mouser to see about a replacement cap data sheet on a Rubycon VXH series 450V 220uF (22mm X 40mm). It's rated for 120Hz.

Maybe if I find some time someday, I go and check others too if they are all rated for 120Hz only.

The original main filter cap from this PSU is a Teapo 400V 180uF 85C, LH series, 2000hr rating.

First I never thought on the main filter capacitance, because usually if there is something wrong it will blow at least the fuse. Since I had checked every single component, couldn't find nothing wrong and hearing the PFC in the light bulb in series trick, it dawned on me better to check the main filter cap properly. I guess the supervisor was faster just to turn the PSU off, before real damage occurs. Pretty clever those ATX PSU's. I usually don't get any ATX PSU's in for repair, but this one was / is for an important computer at work. Also one would think that a bad cap would get hot. This one didn't.

[sam_sam_sam]

Great repair good work one more that did not end up in the landfill