how do i fix my subwoofer

wanky · 3rd January 2008, 02:34 PM

i bought a home speaker system second hand and it has really bad distortion throught the subwoofer channel, all the other speakers work fine. I opened it up and found 2 bulging and dried up capacitors with my ESR meter so I replaced them but the problem still remains. I dont know much about amps what else should i look for with this distortion .f rom what I see its using LM1875T amps for the speakers and using IRFP150 & IRFP9150 for the subwoofer, could these be stuffed? how do i test them?
thanks for help

DSP_Geek · 3rd January 2008, 07:59 PM

Recheck the other electrolytics, especially the large one beside "BAD CAP HERE". If two already went west, likely some others are on their last legs. You might also want to verify the solder joints under the IRF devices, as they looked a bit dodgy to me.

wanky · 5th January 2008, 04:06 PM

i replaced the cap but no difference. i measures voltages of the mosfets while playing audio and they dont change at all

IRFP150 Vgs 3.2v Vds is 49.4v
IRFP9150 Vgs -2.9v Vds -48.9v

should the voltages be the same? also shouldnt gate voltage go higher than that? plz help im trying to learn

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3rd January 2008, 07:59 PM	#2
DSP_Geek diyAudio Member Join Date: Aug 2003 Location: Santa Cruz, California	Recheck the other electrolytics, especially the large one beside "BAD CAP HERE". If two already went west, likely some others are on their last legs. You might also want to verify the solder joints under the IRF devices, as they looked a bit dodgy to me.

5th January 2008, 04:06 PM	#3
wanky diyAudio Member Join Date: Jan 2008	i replaced the cap but no difference. i measures voltages of the mosfets while playing audio and they dont change at all IRFP150 Vgs 3.2v Vds is 49.4v IRFP9150 Vgs -2.9v Vds -48.9v should the voltages be the same? also shouldnt gate voltage go higher than that? plz help im trying to learn