Troubleshooting Sub Woofer Main Power Supply

Thread Starter

bdubyatx

Joined Sep 7, 2022
3
I have a sound bar with a wireless sub woofer. The sub quit working a while back and I finally decided to look in to it. The power LED comes on, but no sound. I figured that the wireless board had gone bad, but when I opened the unit up, If found two badly burned resistors on the main power supply board, and the board itself was burned. I managed to get schematics from the manufacturer (Boston Acoustics) and was able to determine the value of the resistors (they were too burned to read). Page 34 has the schematic for the PS board and shows these two resistors as R08 and R09, both 47ohm/.5W. I cut the resistors out and measured them and they surprisingly still read 47ohm. I understand that resistors rarely go bad on their own, so the problem must be elsewhere.

I also understand that caps (especially electrolytic) go bad over time. I removed C03 and C04 (both 3300uf and 35v) and tested them. I do not have a capacitor tester, but followed some instructions for testing with a volt meter. Check the resistance across the leads several times and if the value never changes, then the cap is supposedly bad. Both caps tested as bad using this method.

My dad, who is more knowledgeable about electronics than I am, but still a novice, thinks the caps are bad, but that there is probably something else wrong that caused too much current. We are approaching this as a fun project to work on together and if we mess something up or cannot fix it, it is not a great loss. It could be a good learning exercise.

If anyone has thoughts on what else we should look at, we would appreciate any tips. I am attaching the full set of schematics which includes not only the sub, but also the sound bar.

Thank you,
budubyatx (Brent)
 

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Thread Starter

bdubyatx

Joined Sep 7, 2022
3
Well, I removed each of those components and tested them. None of them had a short. I replaced the two 47ohm resistors and have ordered two new 3300uf caps. I'll put those in and see what happens.
 
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