How to Repair your Polk PSW505 Subwoofer
JohnsAudio
Posts: 1
I hate to throw things away and I have been repairing amplifiers for almost 20 years so I thought I would find the problems with this sub and why most of them fail.
First thing the class D amplifier design is very simple and should work fine for this application and power level, so I dug into the circuit and tested every component. But every time the components were fine when removed from the board. But in the circuit they were still shorted. To keep this short the glue that was used becomes conductive after it gets hot shorting components. (this is very common on a lot of plate amplifiers made in china) It also appears to be corrosive and while looking at the board through a microscope I noticed that all the SMD components solder joints were corroded. So I scraped all the glue off the board (very carefully) using a dental pick and isopropyl alcohol.
Then covered the board in flux and tinned all the connections on the amplifiers SMD components. When I was done I cleaned the board with alcohol and tested the shorts. They were gone! I repeated this process on 3 different amplifiers and it fixed all of them. You will also need to replace all the small 22uf etc capacitors on the amplifier board at minimum. In my experience the large 3300uf caps don't fail very often. Obviously the best option is to replace all the caps.
I know these subs are hated do to all the failures, but if you want to put in some elbow grease they are savable.
I should probably add that if the board shorted it's possible other components can fail but most of the time the
First thing the class D amplifier design is very simple and should work fine for this application and power level, so I dug into the circuit and tested every component. But every time the components were fine when removed from the board. But in the circuit they were still shorted. To keep this short the glue that was used becomes conductive after it gets hot shorting components. (this is very common on a lot of plate amplifiers made in china) It also appears to be corrosive and while looking at the board through a microscope I noticed that all the SMD components solder joints were corroded. So I scraped all the glue off the board (very carefully) using a dental pick and isopropyl alcohol.
Then covered the board in flux and tinned all the connections on the amplifiers SMD components. When I was done I cleaned the board with alcohol and tested the shorts. They were gone! I repeated this process on 3 different amplifiers and it fixed all of them. You will also need to replace all the small 22uf etc capacitors on the amplifier board at minimum. In my experience the large 3300uf caps don't fail very often. Obviously the best option is to replace all the caps.
I know these subs are hated do to all the failures, but if you want to put in some elbow grease they are savable.
I should probably add that if the board shorted it's possible other components can fail but most of the time the
Comments
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I wish I had your skills!
Great diagnosis on a ton of amp failures!
Thanks for solving the issue of many of these failures that shouldn’t have happened in the first place!Most people just listen to music and watch movies. I EXPERIENCE them.
