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Old 01-13-2021, 04:20 AM   #1
Dannyx
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Unhappy Mini Lenovo PC Dead Power supply (ACbell PCH018)

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 :|
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Old 01-13-2021, 04:59 AM   #2
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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 .
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Old 01-13-2021, 05:23 AM   #3
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Thumbs up Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Quote:
Originally Posted by zen View Post
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...
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Old 01-13-2021, 01:06 PM   #4
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Quote:
Originally Posted by Dannyx View Post
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
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These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

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Old 01-13-2021, 01:22 PM   #5
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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

Last edited by Dannyx; 01-13-2021 at 01:23 PM..
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Old 01-13-2021, 02:53 PM   #6
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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
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Old 01-13-2021, 02:58 PM   #7
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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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...
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Old 01-13-2021, 03:43 PM   #8
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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

Last edited by sam_sam_sam; 01-13-2021 at 03:46 PM..
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Old 01-17-2021, 12:30 PM   #9
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Thumbs up Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

I think I'll need something like this to toggle the fan on and off with the PC (with or without temperature control). The 3.3v is the MB's PS_ON pin of the 6P connector which runs to the PSU. Must admit I haven't done any calculations to work out the value of R1 and R2, assuming the two trannies are 2n2222 which I have on hand currently....and what the current draw of the fan is - they may not be able to handle that much current, even though it's a relatively small fan...
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Old 01-19-2021, 08:48 AM   #10
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Ok, I tried the two-transistor setup in the schematic just for a proof of concept test and it worked......not well enough though: it worked when I tested the setup on an ordinary ATX supply and powered Q1 from the 3.3v rail and Q2 and the fan from the 12v rail, but once I tried the same setup, but wit the 3.3v signal provided by the PS_ON pin of the Lenovo, it no longer worked. The fan turned off alright, as it was supposed to, but also the voltage on the pin itself dropped to nearly 0 and the PC tried firing up as well, which makes sense, since the same thing happens if you ground that pin on a regular ATX....

I think the problem is the pin can't source any current, so any slight load is too much. With this in mind, I tried a FET in place of Q1 and I used whatever I had on hand, which was a FQP6N60C. Same exact setup, except this time I also added a 10k resistor between G and S. It still didn't work: the fan didn't turn off at all this time when I applied 3.3v to the gate of Q1, hinting the D-S junction wasn't closing enough to pull the base of Q2 to GND. It was getting rather late and I was running out of ideas at this stage, so I didn't investigate further. Could be a bad choice of FET or it might be dead and won't open, since I just grabbed it off my desk. It's actually one of the two I used as replacements when trying to fix the PSU in the first place - the one with the "normal" D-S drop when turned on, as opposed to its buddy which has a 1v drop. I don't know a lot about FETs as switches, but isn't an N-channel supposed to open when the voltage at the Gate is greater than the source and draw very little current on the G pin ? Assuming my S was GND and I had 3.3v on G....
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Old 01-19-2021, 03:42 PM   #11
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Why not use a optic sensor like a 4N25 or something similar to this type of device

Last edited by sam_sam_sam; 01-19-2021 at 03:45 PM..
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Old 01-19-2021, 04:20 PM   #12
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Quote:
Originally Posted by Dannyx View Post
it worked when I tested the setup on an ordinary ATX supply and powered Q1 from the 3.3v rail and Q2 and the fan from the 12v rail, but once I tried the same setup, but wit the 3.3v signal provided by the PS_ON pin of the Lenovo, it no longer worked.
u cant use the ps_on pin of a computer psu as a power source or current source. it wasnt designed for that purpose and it wont work. u have to find somewhere else to source your 3.3v supply. i also tried the same thing before as u and i also couldnt get it to work. the ps_on pin just isnt designed for that.
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Old 01-19-2021, 11:50 PM   #13
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Thumbs up Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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Originally Posted by sam_sam_sam View Post
Why not use a optic sensor like a 4N25 or something similar to this type of device
I imagine the PS_ON pin can't source the current required to turn on the LED enough to actually close the transistor...

Quote:
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u cant use the ps_on pin of a computer psu as a power source or current source. it wasnt designed for that purpose and it wont work. u have to find somewhere else to source your 3.3v supply. i also tried the same thing before as u and i also couldnt get it to work. the ps_on pin just isnt designed for that.
Well I imagine the pin CAN do some sort of low-current switching action, which allows the PSU to turn on/off - that's how it works after all - though I think it mostly SINKS current, not SOURCE current...it's probably got a high-ish value pull-up resistor to 3.3v on the motherboard, so it's unable to source more than a few mA, if that, that's why I wanted to try a FET, since the gate current should be very small...
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Old 01-20-2021, 11:23 PM   #14
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

Instead of 10 KOhms for R1, try 100-330 KOhms. Since Q1 only needs to pull about 1.2 mA of current through R2 and knowing that the current gain on these 2n2222 transistors is at least about 100 usually, then the Base current at Q1 could be approximately 100 times smaller - i.e. 10 uA or more should work. Actually, I imagine even less would work, but it would be nice to have a bit of "headroom". If the PS-ON signal still can't source that much current, you might need to go with an op-amp or comparator circuit.

Quote:
Originally Posted by Dannyx
I don't know a lot about FETs as switches, but isn't an N-channel supposed to open when the voltage at the Gate is greater than the source and draw very little current on the G pin ? Assuming my S was GND and I had 3.3v on G....
For N-channel MOSFETs:
When voltage between Gate and Source exceeds the specified Vgs threshold voltage in the datasheet, the MOSFET will conduct between Drain and Source. For good conduction, Vgs > Vd. Otherwise, MOSFET may run in linear/Triode region. Same applies to P-ch MOSFETs, except all voltages should be the negatives of the values specified for N-ch..

Last edited by momaka; 01-20-2021 at 11:24 PM..
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Old 01-20-2021, 11:48 PM   #15
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Thumbs up Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

That schematic was done mostly to show the layout of the components - as mentioned there, the values were not known at that time. I DID go with lower values for R1 and did the math at the time, but it didn't work - pin just can't source the current apparently. It drops to the point where the board actually tries to come on.

Time scarce and the budget must be kept as low as possible (as always), so there's no reason to push forward - I scrapped the idea and just ran two wires to the SATA power connector for the hard drive, since it comes on and off with the system. It's on a separate lead which plugs into the motherboard, so it's switched. The PSU itself has no SATA or Molex connectors at all for that matter - just a standard 4p for the CPU and a 6p, which in reality only uses 5 pins, including that green PS_ON wire which I was going to try and tap into...
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Old 01-21-2021, 12:02 AM   #16
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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That schematic was done mostly to show the layout of the components - as mentioned there, the values were not known at that time. I DID go with lower values for R1 and did the math at the time, but it didn't work
Well, you want HIGHER values for R1 - that is, higher resistance. Lower resistance will only make it worse.

Quote:
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Time scarce and the budget must be kept as low as possible (as always), so there's no reason to push forward - I scrapped the idea and just ran two wires to the SATA power connector for the hard drive, since it comes on and off with the system.
The simplest solutions are always the best, aren't they.

While at it, you should just have wired the PSU fan to the 12V rail on the SATA connector. That way, when system comes on and power goes to SATA, it also goes to fan. No transistor circuits needed anymore!

Last edited by momaka; 01-21-2021 at 12:04 AM..
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Old 01-21-2021, 01:02 AM   #17
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Talking Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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While at it, you should just have wired the PSU fan to the 12V rail on the SATA connector. That way, when system comes on and power goes to SATA, it also goes to fan. No transistor circuits needed anymore!
I think I just said this
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Old 01-21-2021, 01:46 AM   #18
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Default Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

^ Oh.... right you did.
For some reason, I read it that you just took 3.3V from the SATA power connector to drive that transistor circuit.
Yeah, NVM then.
Simplicity Level 300 achieved!
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Old 01-21-2021, 04:43 AM   #19
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Talking Re: Mini Lenovo PC Dead Power supply (ACbell PCH018)

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For some reason, I read it that you just took 3.3V from the SATA power connector to drive that transistor circuit.
I did that just to test that circuit I concocted, which I then abandoned....since, you know, it's not like I have a bench power supply here, so I have to constantly struggle with all sorts of BS methods to do my job, like using an ATX supply as a multi-rail supply......which IS fairly common, especially in the enthusiast community, but this is supposed to be a top-tier company, so it's only reasonable I expect at least a dumb single-channel 3A supply on my desk....
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