Laptop adapter whines, emits RFI when hot

Discussion in 'General Electronics Chat' started by tylerdurden, Apr 6, 2010.

  1. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Hi,

    After warming up, my laptop adapter-charger buzzes loudly and interferes with my touchpad operation.

    I have it running open and the caps are quite hot.

    Would replacing the bigger caps be a good first step?

    I can solder and have an old 10mhz scope.

    Regards,

    TD

    (was on: http://forum.allaboutcircuits.com/showthread.php?p=230406#post230406)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    If the caps are getting hot, they are probably on the verge of failing.

    Replacing them with same-voltage same-uF low-ESR caps will likely help things quite a bit.

    If your adapter has been overheated quite a bit, the transformer insulation may be breaking down. In that case, you'll need to replace the adapter.
     
  3. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Thanks for the reply.

    The transformer is quite hot.

    Output voltage is 19.5

    Adapter specs: 19.5V, 6.3A
    Model: PA3201U-1ACA

    Looks like a cheap unit; but I would like to give repair a try before I shell-out $90US.

    TIA.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Toshibas are usually very good laptops.

    Have you Googled for that model number? I seem to be getting hits in the $20-$30 range.
     
  5. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    I have a similar Toshiba P25 that has been a solid workhorse.

    I was going to get an OEM equivalent at a MicroCenter (brick & mortar). My concern is the cheaper units are lacking adequate filtration, even when new.

    I figure the next supply I get needs to be testable and returnable.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    When replacing caps, it is always advisable to replace all the Electrolytic caps.
    You are lucky the PWM chip is still OK. A bit later and POW!!! There goes the primary
     
  7. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    It's kinda surprising how hot the caps are... I'm familiar with FETs being too hot to touch, but not caps.

    Maybe this unit is simply overrated. I can't imagine it lasting long, running this hot.


    Of course hot temps will help electrolytic caps fail, but can failing caps make it run even hotter?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Indefinitely ..............
     
  9. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    I'll replace all the electrolytics, but I will post the image of the board for reference.
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    tiny little fella...
     
  11. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Well, I replaced the low-voltage caps.

    I could not get the caps for the HV section at RS (also could not find them in any spare equipment); I suppose I'll have to order online.

    I tested with C14, C14b, C15, C15b replaced... not much improvement. Still ran very hot and eventually started whining like a Miley Cyrus fan. Touchpad malfunction returned with the whine.

    Regards,
    TD
     
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    Well I also tend to whine then I am hot. But I guess that will be to much off topic to discuss. So let us stay on topic. It seems like your power struggle to deliver the needed energy. As you have access to an oscilloscope, check the output voltage during load. See if you can spot any transients. Also check the output from the rectifier (the IC next to C12). If one diode of the diodes inside is not working, it could cause such troubles that you have now.
     
  13. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Thanks for the reply...

    I checked the rectifier with my dmm: 54V on each output.

    I have not scoped for transients yet.

    I did parallel a 330uF cap (borrowed from an old PC PSU) onto C12 and the whine is reduced somewhat and the touchpad is better behaved. Also, C12 seems to be much cooler to the touch.
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Replace the 400V Filter capacitor on the primary side
     
  15. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Yeah. Now we're getting somewhere...

    I installed the 330uF cap as C12.

    Barely a whisper from the unit for the past three hours. It still runs hot, but it's quiet and the touchpad works well enough.

    I'll let it burn-in overnight, rendering 3D pipes screensaver.

    Thanks for the tips, I'll report on it tomorrow.


    TD
     
  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Told ya...
     
  17. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Huzza.

    The supply is working reasonably well, after an overnight of moderate-to-heavy load.

    That said, the design of this aftermarket supply seems a bit sparse and marginally adequate.

    By contrast, OEM Sony, HP and Toshiba supplies here have been operating 24/7/365 for 5+ years with no issues.

    But this unit will be sufficient for this laptop, which was recently acquired as a backup.

    Thanks for the advice.

    TD
     
  18. retched

    AAC Fanatic!

    Dec 5, 2009
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    If it is still running overly hot, stay cautious of where you leave it sit. Be sure if it does catch fire, there are no drapes or pile of newspaper near-by to spread flame.

    Is it HOT HOT or just overly warm?
     
  19. tylerdurden

    Thread Starter New Member

    Apr 6, 2010
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    Thanks for the replies...

    The supply is back in its plastic housing and seems no hotter than the OEM unit that is running my other laptop.

    That said, once the unit is warm, the whine is back and the touchpad is again disrupted.

    I'll open the unit again and see if it works properly when cooler.
     
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    seems you have a thermal issue..
     
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