On 07/18/2013 01:00 PM, 170watt wrote:
I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing 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. The PCB 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).


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