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Computer speakers power issue

Discussion in 'Power Electronics' started by THX1138, Jan 4, 2021.

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  1. THX1138

    THX1138

    8
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    Dec 29, 2020
    [​IMG]Hello. I have these old computer speakers. The sound of the left speaker comes and goes depending on how you wiggle the cord. By opening the main speaker (right) I found that the underside of the left power output seems scorched (?). These are harmon/Kardon speakers. According to the power adapter the model number seems to be A481511OT.[​IMG][​IMG] [​IMG] [​IMG][​IMG]
    Code:
    https://bbcode0.com/full/2021/1/4/5180e7aae28640d1ba9b3ace56741313-full.jpg.html
     
    Last edited: Jan 4, 2021
  2. THX1138

    THX1138

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    Dec 29, 2020
    Sorry. I am having trouble uploading images. I think the code I inserted should have the images.
     
  3. davenn

    davenn Moderator

    13,722
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    Sep 5, 2009
    yeah, they didnt show, you may have tried some other format ?

    Use .jpg, around 100kb max, ~ 900 x 600 max

    try again :)
     
  4. THX1138

    THX1138

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    Dec 29, 2020
    B_640x360_320x180.jpg C-1_480x543_240x271.jpg A_640x360_320x180.jpg D_240x426.jpg 20210103_150428_800x450_640x360_320x180.jpg
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    10,833
    2,442
    Nov 17, 2011
    The pcb looks badly corroded. Try cleaning the pcb (use pure alcohol and light pressure, if need be use a light abrasive household cleaner). After cleaning, remove any residues of the cleaning agent with a liberal dose of distilled or purified water and a soft brush.
    Re-solder the affected joints, replace the electrolytic capacitors. After all, the speaker seems to work basically but has obviously a loose contact or cold solder joint(s).
     
  6. dave9

    dave9

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    259
    Mar 5, 2017
    It looks like it had water soluble flux residue remaining on the PCB and then got wet, causing metal salt conductive bridges.

    You may need something more aggressive to clean that off. I usually use (because I happen to have some) brasso metal polish and a toothbrush. It's the mild abrasive particles in it that help more than the oxalic acid. After scrubbing with the polish, then I'd scrub with hot detergent solution and a final water rinse. If it had fine pitch SMD chips I might do a final rinse with alcohol but for that, I wouldn't bother.

    If after scrubbing all that corrosion off, there is bare copper left behind, you might want to paint it to seal off from oxygen, whether it be with a lacquer, conformal coating, nail polish, or anything really is better than nothing, except some coatings could interfere with any later repair efforts and anything opaque, also interfere with ease in tracing the circuit tracks.

    However, I wonder if this is coincidental, that the real issue is one speaker connects to the other with a 3.5mm or similar jack and the spring tension contacts in the socket have gotten loose or tarnished a bit so the manipulation of the cord, even if the power cord instead of the link to the other speaker, is moving the plug in the socket just enough to restore the connection.

    If that's what's happening, you could of course source a replacement socket with same form factor, or do without the connector and solder the wires directly on, or since there is so much empty available space on a speaker housing, just put a hole in the housing for a panel mount jack, air-wired to the PCB contacts.

    Otherwise I don't see how wiggling the cord would be doing anything about the corrosion on the PCB. If the power input socket were intermittent that should affect both channels.
     
  7. WHONOES

    WHONOES

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    May 20, 2017
    A common failure mode with these sort of things is that one of the conductors in the lead fractures close to the connector. This often happens after many years of handling. Try replacing the either just the cable or cable and connectors.
     
  8. THX1138

    THX1138

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    Dec 29, 2020
    I think I might try to replace the cable first before anything else. I have done some soldering in the past but not a lot. Where would I get these cables/connectors? How etc? Also I never remember getting the speakers wet.
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    10,833
    2,442
    Nov 17, 2011
    You don't have to replace the full cable. Usually these break wehre they are constantly moved and bent, typically at the entry to the case, If you can spare a few centimeters, cut the existing cables at a distance of ~ 1 cm from the case, then strip the insulation (use the remaining cable ends as an example). Then solder the nnew cable ends in the same spot where the former cable ends were.
     
  10. dave9

    dave9

    985
    259
    Mar 5, 2017
    Where would you get cables? The internet! Kidding aside, depends on where you're located. A fully made cable might be cheapest on ebay or Amazon while individual connectors, I'd check Digikey, Mouser, etc, electronics suppliers.
     
  11. WHONOES

    WHONOES

    1,034
    282
    May 20, 2017
    I'd go for Harald's suggestion.
     
  12. Martaine2005

    Martaine2005

    3,104
    851
    May 12, 2015
    Me too!

    Martin
     
  13. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    I have taken three pictures from the openings post and rescaled them.
    THX1138_A.jpeg This looks like a deposit of the corrosion of the PCB.

    THX1138_B.jpeg
    Not much to see on this picture.

    THX1138_X.jpeg
    Massive corrosion around the diodes.

    Bertus
     
  14. THX1138

    THX1138

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    Dec 29, 2020
    In the original post by Harald; is pure alcohol the same as isopropyl alcohol?
     
  15. Martaine2005

    Martaine2005

    3,104
    851
    May 12, 2015
    Yes, they are the same. Normally about 99% alcohol. IPA for short.

    Martin
     
  16. bertus

    bertus Moderator

    1,336
    525
    Nov 8, 2019
    Hello,

    There are sevaral types of alcohol.
    IPA is also known as rubbing alcohol:
    Alcohol list.png
    https://en.wikipedia.org/wiki/Alcohol

    I most times use Ethanol when I need to clean something.

    Bertus
     
  17. WHONOES

    WHONOES

    1,034
    282
    May 20, 2017
    The crud in your pictures looks a bit like battery leakage. Have there ever been batteries in your speakers? Or perhaps a capacitor has leaked.
     
  18. WHONOES

    WHONOES

    1,034
    282
    May 20, 2017
    As for the alcohol. Try some undiluted screen wash additive for the car. It is usually Ethanol or IPA or sometimes a combination of the two. It's cheap and it works. Another source in an aerosol is de-icer which is very similar to screen wash.
     
  19. THX1138

    THX1138

    8
    0
    Dec 29, 2020
    Just from a quick look the capacitors haven't leaked and don't look bulged. I added some pictures with a better view of the board. Could the moderator please rescale these?
    20210105_195925_480x853_240x426.jpg 20210105_195810_640x360_320x180.jpg 20210105_200205-1_240x292.jpg
     
  20. WHONOES

    WHONOES

    1,034
    282
    May 20, 2017
    What has been in the corner of the enclosure where all the crud is? Has the box been standing in something?
     
    Martaine2005 likes this.
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