Laptop sound problem

Discussion in 'General Electronics Chat' started by hazim, Jun 18, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Hi all

    I was experimenting a circuit I have built (infrared headphones). I used the headphones jack of my laptop as the source of the audio signal for the transmitter circuit. One of the jack lines is the ground, and is connected to the transmitter ground, the supply voltage of the circuit is a 9V battery. Accidentally, the audio signal line from the headphones jack was connected to the +9V and for several seconds. the wires and the plug became hot, and the laptop sound stopped. I disconnected everything and tried the laptop sound.. even the volume was max. but it wasn't working, no sound. After I restarted the computer, the sound worked! but it wasn't high as usual, the volume was about 1/3 the volume was before. I checked the 'software' issues related to volume and sound device... everything is as normal. When the volume is 100 it's actually low as it's about 30~40.

    At the beginning I thought it would be a burned resistor near the headphone jack, and it stills a possibility. I found a pdf for the laptop circuits you can download it from here: http://www.eserviceinfo.com/download.php?fileid=44467
    In page 26 there are the sound related circuits. Actually I didn't understand them good due to some namings I don't know....

    Any suggestion/idea is appreciated.
    Hazim
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You likely burned out one side of the output amplifier.

    Take a look on page 27, U15. That's what I'm suspecting.
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    I think U15 is completely burned out. That's because the jack is no more working, there is no sound from the headphones. I discovered this now... What I have meant above (the low volume problem-what I said about 30-40%) is about the sound from the laptop speakers. I want to ask if their circuits are built in the motherboard or there is a separated circuit board that can be replaced (sound card?)?
    Thanks
     
    Last edited: Jun 18, 2010
  4. orbiter

    Active Member

    Jun 17, 2010
    58
    3
  5. Razor Concepts

    Active Member

    Oct 7, 2008
    212
    1
  6. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Probably as well or better than the laptop audio card itself did.
     
  7. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Thank you all.
    For now I'll let it as it is.. The volume is acceptable, but for sure I'll try to fix it when I open the laptop later.
    Thanks
     
  8. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Hi.
    Back to this old thread.. I've opened the laptop and made some testing on the motherboard at the audio circuit area. What I discovered is that there was some missing components in the audio circuit. The main missing thing was a surprise for me, it is IC U15. I don't think it had "exploded" and disappeared, but it wasn't used in the model of my laptop.. The Circuit board is clean and there is no appearance for defective components.

    By testing for shorted components I found a short between both terminals of each of two (or 3 I've forgot) SMD capacitors. I didn't tried enough to point the location of the short but I tested the transistors and diodes there and didn't find a short with them.

    I reassembled the laptop without fixing the problem. But the disappointment is what I found after reassembling, the volume became much and much lower and even the sound became not clear enough. The volume is now looks like it is on 10 when it's actually at 100...

    I may get one as that in post#5 but I need to have a good sound from the laptop speakers.

    I know I should try to locate the shorted component and fix it but I'm afraid to get no sound next time I reassemble the laptop :confused:

    Regards,
    Hazim
     
  9. orbiter

    Active Member

    Jun 17, 2010
    58
    3
    As SgtWookie says.. It does 'sound like' (excuse pun) part of the amp circuit is dying.
     
  10. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    orbiter, SgtWookie talked about U15 which is not on the circuit board as I said. There is a place on the circuit board for it, 'U15' is printed there but it isn't soldered there. Some of the components which are connected to it (in the circuit) are not implemented also.
     
  11. orbiter

    Active Member

    Jun 17, 2010
    58
    3
    Sorry hazim, I meant the amp circuit in general, not a specific point of it. I'm no specialist in this area so would not like to point you towards an exact point of failure.

    regards

    orb
     
    hazim likes this.
  12. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Not a problem. Thank you anyway. I'll try to fix it, but if I failed I'm thinking to use an empty place for an additional hard disk I have in the laptop. Yes I have a hiding place inside my laptop :). I could get one external USB sound card as that linked to in post#5 and connect it to one of my laptop's four USB ports, use a small stereo audio amplifier powered from the same USB port or if 5V is low I'll get power from another place, laptop battery for example. If I didn't find a suitable amplifier I may build one using two (stereo..) LM358 for example, TDA2822 is a 8-pin DIP dual audio amplifier that can deliver about 2x0.65W to 4ohm speakers using 5V supply voltage but I don't know if this output power is really enough to get high volume. Any recommendation for another IC is appreciated.

    So I can make these and put all inside that hiding place with connections all inside the laptop, to the speakers and power source and a USB port.

    It's a good idea right? :)

    Regards,
    Hazim
     
  13. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    I built a small audio stereo amplifier circuit supported with TDA2822 datasheet using this later IC. Connecting the USB audio sound card adapter to the amplifier worked fine with two 4 ohm 3W speakers on my mobile with 5V power source. I connected it to my laptop and got high distortion even when the volume level is low, so I added two 47k trimmer pot. at the inputs of the amplifier and adjusted them... Everything is connected internally and it works just perfect.

    Regards,
    Hazim

    [​IMG]
     
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