Mini Lenovo PC Dead Power supply (ACbell PCH018)

[Dannyx]

Good day folks. It's been a while since I've fixed a PSU and it shows with this one, as I can't seem to figure out how it works and what's wrong with it.

Fuse was open (though not obliterated) and the two transistors shown were shorted. The originals pictured up-close are AP50WN1K5I and I couldn't find the exact match. They looked pretty standard in terms of specs, so the guy at the store looked over some datasheets and gave me two FQPF6N60C instead. The datasheets are indeed pretty close, except the replacement ones are a bit more resistive. I though it wouldn't be a deal-breaker and would work first-try...unfortunately it didn't...

No catastrophic failure occurred but I got no boosted voltage on the main cap (stuck at 325v) and I got no output at all...after trying it a second time, I think I saw some smoke coming out. I couldn't see where it came from, since I quickly unplugged...I managed to quickly measure the AUX winding to see if the control IC, a TEA19161T gets VCC, but the winding is dead....

I measured the gate drive portion of both trannies and ironically everything checks out fine, so again, it could be that smoke was just my imagination, ALTHOUGH: I removed the trannies again to see if they died and the answer is "sort-of", meaning they're not dead-shorted, but one of them measures weird. Get this: I put them side by side and used my meter in diode-mode:

1. RED probe on D and BLACK probe on S gives me nothing (which is normal)
2. RED probe on S and BLACK probe on D gives me 0.55v which is the body diode (also normal IMO)
3. RED probe on G and BLACK probe on D gives me nothing on both of them, (which is normal). This should also "open" the D-S path...
4. now, RED probe on D and black on S gives me 0.38 on one and 1v on the other one. THIS doesn't seem normal to me. I think the good one is the one with the lower reading.
5. strangely, after "opening" the transistor again, if I go RED on S and BLACK on D, I get 0.1 on the "good one" and 0.2 on the "faulty" one.......what do you guys make of this ?

Should I bother to replace the TEA control IC ???

This is a strange PSU: it's only got a 12v output, yet it still has a green "PS_ON" wire.....how does this work ? The yellow wires are all bunched together, so how can there possibly be a "stand-by" voltage ? Even if 12v WERE the standby voltage and were on all the time, what's the purpose of the green wire then ??? It could be it's just the color that's similar, but in reality it could be a power-good signal...I was hoping I could replace the supply entirely with a 12v one, but it will be missing this signal and refuse to turn on......really sucks this one :|

[zen]

Hello

Due to previous experience , i never replace chopper F E T S , without replacing the control chip also , as well as checking all the surrounding components .

I have repaired many power supplies & found this to be the most reliable way to prevent failure .

I also use a v a r i a c , after repair , to very gradually increase the AC supply , in case there still is an issue with board , as it can prevent additional damage from ocuring .

[Dannyx]

Originally Posted by zen

Hello

Due to previous experience , i never replace chopper F E T S , without replacing the control chip also , as well as checking all the surrounding components .

I have repaired many power supplies & found this to be the most reliable way to prevent failure .

I also use a v a r i a c , after repair , to very gradually increase the AC supply , in case there still is an issue with board , as it can prevent additional damage from ocuring .

Aside from the control IC, I did check just about everything related to the gate of those transistors. True, I also like to use a series lightbulb but I don't have one on me right now so I just YOLO-D it....it might all boil down to the control IC, esp. since I forgot one key detail: the 10ohm resistor (R23) encircled was open-circuit when I first inspected it, so some current may have leaked into the control pin of the IC and damaged it...

UPDATE: PC works with just 12v going into it - I hacked a 6p connector and used a regular ATX supply to power it and the PC booted fine, so the idea of hacking a MeanWell in there is becoming doable...

[sam_sam_sam]

Originally Posted by Dannyx

UPDATE: PC works with just 12v going into it - I hacked a 6p connector and used a regular ATX supply to power it and the PC booted fine, so the idea of hacking a MeanWell in there is becoming doable...

This would probably be the best way to resolve your issues with the switching power supply

I have found that MeanWell switching power supply are very well built and most of the time they use brand name capacitors already and you do not have recap them

[Dannyx]

I found a "bare" supply from MeanWell which fits inside the metal case of this one with room to spare and even seems to match the fan and AC connectors. I was going to mount this on some stand-offs in place of this board so the whole assembly still fits inside the case like before. Everything was going well except these chaps told me it's too expensive, so it looks like I'll try swapping the TEA IC too...maybe they'll give in and eventually go with my idea

The only caveat is the fan would run non-stop which will surely make some folks uneasy I was planning on using a PNP tranny and tap into that green "PS_ON" signal to switch it on and off as the PC pulls that pin HIGH/LOW. Yes, it turns out it's not a PG signal - it's a PS_ON signal, as it reads 3.3v when the PC has 12v going to it but it's in S5 and gets pulled to GND when it's turned on, so my transistor or whatever I use would have to work in reverse: 3v means OFF, 0v means ON

[sam_sam_sam]

Why not use a temperature controller for the fan and put the sensor on the heat sink if it has one and if not then mount the sensor on the device that would have the most heat coming from it

[Dannyx]

Originally Posted by sam_sam_sam

Why not use a temperature controller for the fan and put the sensor on the heat sink if it has one and if not then mount the sensor on the device that would have the most heat coming from it

That would be the "ideal" solution, but where does one obtain a fan controller ? I think I actually ripped some out of ATX supplies - they're small standalone boards with an NTC sticking out of it. I'd still need the PNP to turn it on/off...

[sam_sam_sam]

If you get one out of an ATX switching power supply some of have a small circuit board that controls the fan and all it requires is 12 volts and the use of the fan that it is hooked to

FSP 300 ( ATX ) switching power supply have a small circuit control board and easy to use

You can also find them on eBay as well