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Need suggestions repairing PSU

Discussion in 'General Hardware' started by grandpatzer, Nov 27, 2013.

  1. grandpatzer New Member

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    Recently I replaced fan in the PSU, The fan molex pressed the green pcb card and made it move.
    My suspicion is either soldering got loose on powerplug or a component on that green PCB got damaged.

    I have a soldering Iron + multimeter, I'm going to disassemble the PSU.

    Now I need suggestions what to look for, can I make some multimeter measurements to figure out if a soldering is broken or some component on that PCB card?
    From wall using the Black/Green power on Trick I get following:
    Power OFF: 0.0watt, Power ON: around 0.6 - 0.7 watt, I live in Sweden and we have 230volt system here.

    If a component is damaged my guess would be it's one of the ones on top right corner on this picture, this image is from jonnyguru review of this PSU:
    [​IMG]

    These 2 images are on my PSU and show the molex fan.
    [​IMG]

    [​IMG]
     
  2. SaiZo

    SaiZo

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    You mean that the fan header (white one, picture two), was pushing down the PCB with force?
    I guess you could add new solder to the parts that are "loose", but make sure that the PCB itself isn't damaged.
    Had similar issue with the transformer on an HP screen a week ago, the power in socket was loose, but the PCB was too damaged to be repaired.

    Try not to get a shock or start a fire, I know that the insurance companies here in Sweden are a pain in the @$$..
     
  3. SKBARON

    SKBARON

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    Even if the pcb is damaged, if it isn't multi-layered, it could be fairly easy to trace contacts and do some ghetto repairs :).
     
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  4. grandpatzer New Member

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    I think need to use screwdriver and screw off the PSU internals to get good look at that tiny PCB, I think the powerplug is attached to the case, obiously the powerplug is to close for me to know if PCB is damaged as there is only a small gap between them.

    If I succeed reapiring the PSU, what's the best way to test it before installing it in my PC?
     
  5. SKBARON

    SKBARON

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    You could use a paperclip or something like that to turn the psu on. A little info on that can be found here:

    http://www.techpowerup.com/articles/other/22

    You can use a multimeter to check voltages and stuff to see if the psu is functional.
     
  6. grandpatzer New Member

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    It was workin fine, after I replaced the fan it did not work, after I put in a new fan I did try with paperclip the PSU and neither the internal or external fans started up.

    I believe the problem is that tiny daughter board that the fan plug made move about 1cm, I think it could be damage to soldering.

    Can I do some multimeter measuring or should I just take a magnifying glass and look for damage to soldering.

    I guess the damage could be one of these 4 places: daughter board front, daughter board back, main PCB up, main PCB down.

    Here is 3 pictures showing the daughter board fron/back, main PCB bottom, it's not my unit but same model I found on internet:

    [​IMG]

    [​IMG]
    [​IMG]
     
  7. SKBARON

    SKBARON

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    Could you try posting bigger pictures? From what I'm seeing on the last pictures are some contacts that are lifted/ripped of the pcb, but I can't be sure since I can't zoom in on in. Try posting these pictures in spoilers.
     
  8. grandpatzer New Member

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    Those pictures are not mine but from a review (on this same PSU model).
    According the review the soldering was good and some of it was hand made soldering.

    I can disassemble the PSU and take pictures ofcourse, btw is it possible to measure with multimeter any of those legs on the daughter board?

    not sure what to look for when measuring them.
     
  9. SKBARON

    SKBARON

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    It would be helpful to see pictures of your psu. You should measure voltage I guess, or current, to see if it goes from one point to another, I mean to see if the current is "travelling" from point a to point b and everything is intact. But since you said the psu isn't powering on, something, somewhere must have broken.
     
  10. crmaris

    crmaris Reviewer

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    avoid messing with the PSU especially if this is connected to the mains and given that you aren't a pro. The current can kill you!!

    Also even if you remove power the APFC caps hold enough charge to make quite a bang and of course electroshoot you so beware.
    You have to discharge the APFC caps before you put your fingers on the PCB in any case.

    The daughter-board feels loose to you? If you can try soldering again all of its joints even if they look good.

    And for the last time be careful! Don't touch it without discharging the caps I mentioned. I use a pretty long and thick wire with a resistor (10 Ohm, 25 Watt) to discharge them. But usually I run it full load and cut suddenly power via the mains switch so the caps are already discharged (something you cannot do since the PSU isn't working as you say).
     
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  11. grandpatzer New Member

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    So I finally inspected the PSU closer and found the problem mostlikely, this tiny black square "memory module" labeled LG had been ripped of the top solder point, it seemed to still be held together by the 2 bottom solder joints (so 2 bottom 1up in total) however when I tried using a tiny screwdriver to move it back up it came completely loose.

    [​IMG]

    Here you can see it's not connected to the solder joint:
    [​IMG]


    Question what is that thing and I guess I need to replace it?
    I tried some soldering and now the LG label is no longer visible, if these things are heat sensitive (soldering station 380celsius), I might have to buy a new one somewhere (ebay?).

    Finally after trying pretenning the chip I decided to use some tiny wire to the daughter board itself, now I need to careafully make solder connections. BTW I think my soldering station is 1.0mm or 0.5mm, and this thing is tiny chip / soldering joints!!!!!!

    [​IMG]
     
    Last edited: Dec 1, 2013
  12. SKBARON

    SKBARON

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    You should see if the contacts on that thing are still intact, chances are they were ripped out of it and remained with the solder on the board. I have no idea to be honest what it was, but you could try asking around on the forum or on some specialized forums what it is. Don't use wires because they can mess with things.
     
  13. McSteel

    McSteel

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    That's most probably an SMD BJT. It's purpose and function was probably as a part of a discrete signal amplifier, used in the feedback loop to the 14-pin SMD controller IC situated on the vertical daughterboard. I presume that it's the secondary protections/supervisor IC, from it's location within the PSU. I think I see a 8-pin DIP IC that I suppose is an integrated OP-Amp, but I can't be sure. Your photos are super-useless, being both tiny and taken from typical facebook/myspace angles.

    The broken-off SMD BJT looks to be damaged beyond repair, but those are about $5 for 100 pieces, so that's not really an issue. The real problem is figuring out it's characteristics, or even if it's NPN or PNP type. Since it's probably used for signal amplification, it's probably the latter. The fact that it's missing most probably means the protections IC is preventing the PSU from fully powering up. You should check to see if you have 5VSB operational. Use a multimeter to measure between the purple wire pin and one of the black wire pins on the 24-pin ATX connector, you should get between 4.75 and 5.25V there. It would signify that your primary is alive and kicking, and so is your stand-by, leaving you with non-functional secondary, due to a disruption in secondary IC functions.

    Adequately replacing the damaged SMD BJT would solve such an issue.
     
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  14. grandpatzer New Member

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    Thanks, I'll take better pictures and pos in thread, as for that SMD BJT or whatever it is, is there some "trick" I can do to get this PSU going without the black square thing?
    Is it critical to have that square thing inside the PSU?.

    I guess I have to plug to wall the PSU and measure to see if I'm getting 4.75 and 5.25v from the black and purple wire.
     
  15. McSteel

    McSteel

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    Well, since it's a transistor - and nothing mimics a transistor better than a transistor - I think you should replace it accordingly. If you were to simply short some contacts instead, you'd get a non-functional, or potentially hazardous power supply. The vertical daughterboard holds a logic circuit that determines whether the power supply outputs correct voltages or not, and shuts it down if and when it doesn't. It also usually acts to protect both the power supply and the components from accidental short circuits or overloads. Impeding it's functions is a very bad idea however you look at it.

    If you're not familiar with what a transistor is and how it works, I suggest you read up on it before taking any further action here.
     
  16. grandpatzer New Member

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    so how do I figure out the exact model of that transistor so I can order a new one to solder in, this one must have had it's legs broken I guess, there where no legs to solder.
     
  17. McSteel

    McSteel

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    There's no real easy way to do it. You could use the diode test/continuity test function on your multimeter, and do some probing/measurements between each leg stump in both directions, this could give some clue as to which leg is which (base, collector emitter), and we could possibly infer if it's a PNP or an NPN transistor.
     
  18. grandpatzer New Member

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    so what happens if I bridge the 3 solder points with a wire?
    I loose overprotection for PSU?

    BTW can I try the PSU without that transistor?
     
  19. McSteel

    McSteel

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    I don't know what exactly happens. You could simply lose one of the protections. Or your PSU could output wrong voltages and potentially damage your other hardware. You can't know without trying. You could even fry some other components of your PSU, further damaging it and reducing chances of successful repair.

    You can try the PSU without the broken transistor, and it should actually output 5VSB (5 volt standby), even if the secondary doesn't work properly. Just don't try it on your hardware without checking if standby works (purple-black) and trying to jump-start it by shorting the green wire to one of the black ones, then measuring between yellow and a black (12V), red and black (5V) and orange and black (3,3V). If everything looks fine, you're one step from having a fully functioning PSU.
     
  20. SaiZo

    SaiZo

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    Elfa Radio - https://www.elfa.se/elfa3~se_sv/elfa/init.do?init=1&shop=ELFA_SE-SV
    Take the component with you, they will know which one you will need, or try a search there.
     
  21. grandpatzer New Member

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    So if I do those measurements without the transistor installed and all shows correctly I have a working PSU(?).
    Is there anything else I need to consider regarding that transistor.

    Thanks I know of ELFA, it's a bit long distance from me.

    So, I spent alot of time trying to solder it in there, it has no legs so I think the transistor is broken?

    I tried using tiny wires but I doubt that helps, this is impossible to solder, maybe I would have more luck if I got a identical transistor, it's labeled LG, on this picture you can see one like the one I need on the bottom, also you can see the three wires I soldered to keep the transistor connected (failed)

    please click on picture for larger, as I said the transistor I need is like to one under it labeled "LG"

    [​IMG]
     
  22. SaiZo

    SaiZo

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  23. grandpatzer New Member

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    That alibaba link could very well be it, I'll read that link you posted and try to measure with multimeter the "healthy" transistor that is on the PCB bottom in soldered, I think the loose transistor will be difficult to measure with my multimeter.
    I have a cheap multimeter.

    I don't live in Sockholm SaiZo, is he someone who has this kinds of components or do you mean help me figure out the transistor I need?

    If he has these kind of stuff I'm happy to buy a transistor/s once I figure out what I need.

    Another "problem" I have is that it's going to be difficult to solder in red and black wire to PSU casing unless I rip off the glue, I would rather not remove the glue because I don't have strong enought glue to keep it held together to PSU case after re assembly, I'm mostlikely going to solder Red/Black wire to the back of the PCB, I think this should be safe?

    [​IMG]

    [​IMG]
     
  24. SaiZo

    SaiZo

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    No, what I meant was I could dig around and see if there is anyone nearby your city/town who can take a look at it. We used to have a guy who could repair delicate stuff like that, but also find out the correct component.
    Are there no numbers or anything else than LG on it? I found nothing on "LG", but "LGE" had some components..

    If you have any electronic "junk" at home, that could have the same component, perhaps try that - without having it connected to the computer if possible (just like McSteel suggested), since damaging your hardware would not be a good option.

    Get a gluegun (limpistol), for the PCB holding the AC in (the one with the green/yellow ground wire).
    Since I do not know what stores you have where you live, try like Kjell & Company, Clas Ohlson, Biltema, Jula etc. Biltema have the lowest price, sometimes ICA Kvantum stores even sell glueguns.

    As for soldering the black/red wires back on, I would do it the hard way and solder them the way they were. But if you are limited to if you can buy a gluegun, I (guess) you could solder them from the other side.
    However since I do not know how it looks on the other side, it's difficult to tell if it's the correct approach.
     
  25. grandpatzer New Member

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    sadly the transistor says nothing else besides LG, I think it's possible it's that LGE company that makes them, unless it's the actual big LG (smartphones, tv's etc).

    I actually own two glue guns, one specified 170celsius and one mini low heat glue gun specified 95celsius.
    I only have glue stick for the mini, so I would have to buy some glue stick for the 170celsius gun, I guess the 170c heat glue gun is OK for the PSU.
    Even though it's rather old it should still work, it's propably bought at Claes ohlson or Kjell & company.

    But I think I'll just solder in the red + black wire from backside of the PCB on the AC, because for removing the Red and Black wire I heated the 2 big solder blobs on the PCB to remove them.
     

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