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Harman Kardon SUBTS15 subwoofer very faint sound

I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing it myself. I have basic troubleshooting experience (including solde ring 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 secon ds turns blue (and stays blue). At that moment you can hear a loud thump (c ouple of thumps actually). While on, there is no sound coming from the spea ker. 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 p owered down, another thump. What I checked: the relay works both when turning on and off (both times co incide with the thumps). The +/- 15 V are both OK. At the visual inspection , there is some discoloration (darkened color) of resistor R146 and 149 (es pecially 146 that looks a bit burned) but both test correctly 330 ohms. The PCB around them also looks a bit darkened. Any idea where to look for? I doubt that the issue comes from the ?darken ed? area. The troubleshooting flow chart does not help, as the led does n ot turn red or green (only blue, and stays blue).

Reply to
170watt
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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.

Reply to
William Sommerwerck

Check for DC on the ouput. Anything above 50mVdc indicates issues with the power amplifier stage.

Reply to
dave

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up"

the

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. T he "normal" sound, played during music reproduction cannot be heard.

Reply to
170watt

ry fixing it myself. I have basic troubleshooting experience (including sol dering skills), but I don?t know what I should next (besides tossing it).

onds 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 sp eaker. If you feed a signal (at the line level, with test tone from receive r), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.

coincide with the thumps). The +/- 15 V are both OK. At the visual inspecti on, there is some discoloration (darkened color) of resistor R146 and 149 ( especially 146 that looks a bit burned) but both test correctly 330 ohms. T he PCB around them also looks a bit darkened.

ened? area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).

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

Reply to
170watt

If you have a diagram and a scope you know what to do.

Reply to
dave

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