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Harman Kardon SUBTS15 subwoofer very faint sound

Discussion in 'Electronic Repair' started by 170watt, Jul 18, 2013.

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  1. 170watt

    170watt Guest

    I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to tryfixing it myself. I have basic troubleshooting experience (including soldering skills), but I don’t know what I should next (besides tossing it).
    Here’s what it does, and what doesn’t.
    When I power it up, the front led lights amber, and after a couple of seconds turns blue (and stays blue). At that moment you can hear a loud thump (couple of thumps actually). While on, there is no sound coming from the speaker. If you feed a signal (at the line level, with test tone from receiver), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.
    What I checked: the relay works both when turning on and off (both times coincide with the thumps). The +/- 15 V are both OK. At the visual inspection, there is some discoloration (darkened color) of resistor R146 and 149 (especially 146 that looks a bit burned) but both test correctly 330 ohms. ThePCB around them also looks a bit darkened.
    Any idea where to look for? I doubt that the issue comes from the “darkened” area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).
  2. According to the owner's manual, what do the various LED colors indicate?

    The thumps suggest that the output stage is receiving power. That you can't
    get anything out of the woofer suggests that the signal is getting "hung up"
    somewhere before the output stage.

    Also make sure that all the settings are correct.

    Note that the test signal has to have significant components in the range the
    woofer is designed to to reproduce.
  3. 170watt

    170watt Guest

    The user manual only indicates the amber and blue (normal) colors, whereas the green and red are mentioned in the service manual, which is confusing. The test signal was generated by the receiver, for the subwoofer channel. The "normal" sound, played during music reproduction cannot be heard.
  4. 170watt

    170watt Guest

    Thanks for your answers. I haven’t used this forum before, I think I inadvertently deleted one post, and also was not sure how to reply specificallyto the author, I might have done this already, sorry for double posting.
    I checked the DC output, it’s below 10mV.
    @ William:
    The color LED mentioned in the user manual are amber and blue (normal functioning). The troubleshooting diagram in The Service Manual also mentions green and red, which is confusing. The test signal was generated by the receiver, with the signal test function activated, via subwoofer pre-out.
    @ Arfa
    I have the manual, from the same source you mentioned.
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