Analizing and reparing Laptop's chargers

Discussion in 'General Electronics Chat' started by ElectroBoy7, May 3, 2016.

  1. ElectroBoy7

    Thread Starter Member

    Dec 22, 2015
    33
    0
    Hello everyone! It has been a long time since my last post and I was wondering about what to ask next so here I am.

    As I explain in the video, my laptop's carger has broken and is not working at all anymore, where I should be getting at least 19 Volts, I'm getting a big 0!
    So I did the non-invasive tests such as checking both cables, the 220V AC cable and the 19V DC cable, both work fine so it is clearly the problem is inside the charger So I opened:



    I hope you can help me out!

    Bridge Rectifier datasheet: http://pdf1.alldatasheet.com/datasheet-pdf/view/253062/VISHAY/GBU8J.html

    Metalized polypropylene film capacitor: http://pdf1.alldatasheet.com/datasheet-pdf/view/586592/OKAYA/LE334M.html

    I took the schematics from here: https://www.power.com/sites/default/files/PDFFiles/der243.pdf
     
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    How about the Fuse on the incoming line?
    I'd replace the TDP switch......
     
  3. ElectroBoy7

    Thread Starter Member

    Dec 22, 2015
    33
    0
  4. NoelSof

    New Member

    Sep 22, 2015
    10
    0
    Hi,
    you can check the fuse first and see if it's blown or not.
    Visually check that there's no bad/crack solder join, check the output capacitors, do a continuity test on the cables, also make sure there's no short circuit. Anything above that you can just buy a new one :p
     
  5. ElectroBoy7

    Thread Starter Member

    Dec 22, 2015
    33
    0
    Thanks for the comment!
    Well indeed, I could just buy a new one but I'm doing it because I want to learn more about each component.
    How can I check that the fuse is broken ?
     
  6. NoelSof

    New Member

    Sep 22, 2015
    10
    0
    It's hard for me to see things in this video (why not use a photo?), but I think the black box near the mains input is the fuse box. Open it and remove the glass fuse, test it with a multimeter. Google out images of 'blown glass fuse'.
     
  7. ElectroBoy7

    Thread Starter Member

    Dec 22, 2015
    33
    0
    In the video I also said that that little box is the FUSE box.

    This one can't be opened but this video:



    says that a FUSE is basically a resistance so when I make a continuity test, it should sound but it doesn't so that might be the problem. I'll check into this a bit further and let you know. Thanks !
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Circuit diagram wont open, its a switchmode psu, the mains will be rectified to 380v dc across the large capacitor, find which chip it uses, from past experience its more hassle to fix these than buy a new one.
     
  9. ElectroBoy7

    Thread Starter Member

    Dec 22, 2015
    33
    0
    Thanks for you help. As I said before I'm just doing it because I want to learn more about electronics by trying to fix something because that way I have to investigate about every little component.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    Since you obviously lack experience, be aware that at least one capacitor in the circuit, when charged, holds enough charge at high voltage to KILL you. Never poke around inside until at least five minutes after you have disconnected the mains power lead.
     
  11. NPN-1

    New Member

    Mar 11, 2016
    6
    0
    what is the best way to discharge such charged capacitors?
     
  12. wayneh

    Expert

    Sep 9, 2010
    12,120
    3,046
    Ever been to an electronics recycling center? There are piles of dozens of these things. Most are still working. Just go rescue one from recycling. Stop risking your life to repair something of zero value.
     
  13. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    Is that the exact schematic for your power supply? It looks like the schematic is for a reference design, and the actual board you have is some other commercial product. There are more parts on your board, for one thing.

    I have never seen a bridge rectifier go bad, at least not a silicon one on a heat sink like you have. Most likely it is ok. It is normal to read some resistance across the AC (middle) pins of the bridge, while in-circuit, at least temporarily. There is a large capacitor across the + and - of the bridge, and while your multimeter charges that, it will read something. If you want to learn about the components, unsolder the bridge rectifier first, then test it. But if you want less trouble, just measure between the brown and blue wires (or the pins of the AC power plug). If there is infinite resistance there (your multimeter shows a '1', even when set to the 200k ohm range), then most likely, a fuse is blown.

    And if a fuse is blown, don't just replace the fuse. Something was drawing too much current. The main switch (MOSFET transistor) is often the thing that goes bad. In your case, it's that TOPswitch part. Measure between D and S with your multimeter, and if you see a low resistance both ways, the transistor is no good. When they fail, they usually fuse into one resistive lump between all pins.

    At that point, I would typically abandon repair efforts as a practical matter. If you want to learn how switching supplies work, it's better to study a good one, than try to learn from a bad one. If you still want to try to fix it, without understanding the theory of how it works, blindly start testing every component in the area. Especially look at any semiconductors, and make sure resistances are of the value printed on the resistor. You may need to unsolder components before testing them. In my experience, inductors and transformers never go marginally bad. They can fail catastrophically, but in that case, you will see either burns on the wire, or read an open circuit ('1' on your multimeter).
     
    NoelSof likes this.
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    In a properly designed supply there will be a high value resistor connected across the cap to bleed charge away when the mains power goes off. The safest way is to have patience and just let it do its thing.
     
    NPN-1 likes this.
  15. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    Imo I just throw the laptop chargers in the trash and just grab a used one off ebay.. Also remenber that with a repair there might be another issues and possibly fry the device.. The only way I save them is if the plug goes bad and it can be replaced..
     
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