Laptop PSU gone funny

Discussion in 'General Electronics Chat' started by DigitalReaper, Sep 25, 2010.

  1. DigitalReaper

    Thread Starter Member

    Aug 7, 2010
    70
    2
    I've got a laptop charger here that's making strange noises. It sounds a bit like the squeal some graphics cards make, but the pitch and intensity varies with load.

    This has just started happening, right after I replaced a damaged power connector (laptop end). The new connector is on correctly with no apparent shorts, the laptop does charge from it.

    Is this thing safe to continue to use or is it ready for the bin? Or is it worth trying to open it up to fix it?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    I would check the electrolytic caps. They can make a sequel, ala camera flash charging.
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    My charger doesn't do this, but my laptop does. Only during a certain part of the charging cycle (about 60%-80%) the laptop emits a high pitched whining sound. It's not very audible (you can hear it if the room is quiet), and I've had this laptop for almost 2 years now with no notable problems. Like your charger, it varies with load: the pitch changes if you change the screen brightness, or start a program which uses the CPU lots. The charger has been replaced 3 times though - they fail like nothing else - but in all three cases it was the wire in the connector to the laptop breaking, not the charger itself. It's a Dell Studio 1537.

    It's probably next to impossible to repair them. I remembered trying to open them. They are completely sealed shut. A hammer seems to open them, but causes significant damage to the internals. :(
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Only change was the connector, it's probably been bad for some time, battery probably got real low, it's just charging.

    It may stop on its own after several battery charge/discharge cycles or the battery may be getting to the end of its life.
     
  5. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    marshal he said the power supply is make the noise not the laptop, it shouldn't have anything to do with the battery, although if you want to be sure you could check the laptop supply using a dummy resistor as a load, I can see that some kind of feedback from the laptop could be causing it but that seems unlikely to me.

    It could be the SMPS transformer has developed a crack or has a loose winding, it explains the varied pitch and volume you're hearing with load. Could mean nothing could mean it's ready to blow up at any moment, could be a capacitor too but the plastic cases on those things are usually welded shut so it's not easy to pop it open and take a look around.

    reteched, if I'm not mistaken the noise a camera flash makes is from the transformer windings not the capacitor, try attaching a suitable load resistor in place of a camera flash cap and see, I'm curious.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,753
    760
    You are having capacitors that are drying.
    The Adapter has to be cut open.

    I always use my dremel with a saw blade. All it needs is a few mm deep cut around and viola!! it's open. U can re glue it like new & no one would be wiser
     
  7. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    ha yeah right, it's not that easy Rifa, I know I've taken bricks like that apart before, once you get it apart you'll never it safely back together again it a trustworthy usable state. It'd be good to take apart for bits but once it's apart I'd never use it again not for a laptop at least, if you don't trust it buy a new one.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,753
    760
    I don't know about u but I do this all the time :cool:
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    If the battery had gone down farther than it ever has the charger was getting called upon to produce more current than usual.

    When something quits right after working on it its best to eliminate the most obvious why would its.
     
  10. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Lithium ion batteries are charged with a constant current to a fixed voltage and then the voltage is maintained until the charging current drops to about 10% of it's constant current charge rate. 1% or 75% they'll charge at the same current so that doesn't make any sense. Again though as I said above if you suspect something weird with the laptops charging circuit might be causing it all you need is a power resistor to check the adapter as a dummy load.


    Rifa I'd love to see some pictures of those glued back together supplies...
     
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    We don't know what kind of battery is in it.
     
  12. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Wouldn't matter, NiMh's are charged constant current as well until the voltage dip of the cells peaking is detected. So would Nicad's be for that matter. Come to think of it even a lead acid battery would be constant current charged as well.
     
    Last edited: Sep 26, 2010
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,753
    760
    Ok then. Next one that comes in for repair will be documented especially for u.
    But there is one more thing I had to buy, this post reminded me.
    It's abt time I get some new mini saw blades. The ones I have a like a coin now :D

    and by the way. Laptops use li-on's
     
  14. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Older laptops used NiMH's, you can still buy replacement batteries for them. NiCad and Leadacid I'm not so sure about but I'll guarantee someone could probably hunt one down that did =)

    Rifa, before I make an ass out of myself, post a link to the blades you're talking about.
     
  15. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    New ones do, but I've still got one I use for a piece of diagnostic equipment that has a NiMH battery in it - it originallly came with a NiCd.

    Why you might ask? This diagnositic equipment requires an RS-232 serial input which they seem to have stopped including on newer laptops and most of the RS-232 to USB converters aren't cheap.

    The last few PCs I built didn't even have connectors on the motherboards for floppy drives and, needing one on occasion, I had to rig in a couple of those USB ones designed for laptops.
     
  16. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Where do you shop?! I think mine cost 15 dollars.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,753
    760
    Let me see. give me a few hrs to track down that seller
     
  18. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    The (Apple) Macintosh "Portable" used a lead acid battery. I use portable in quotes because it weighed about 7.2 kg and was about as portable as a desktop computer, but had a built in LCD, keyboard and mouse. A significant part of its weight came from the lead acid battery.
     
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,753
    760
  20. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    I've since found them for $6 but back when I first started looking years ago (it was my only laptop) the thngs were over $100

    I still use the old one though because it's a lot simpler and the tester fit into the carrying bag so that's all the service it sees anymore.
     
Loading...