I've had a Polk speaker system with subwoofer in my home for over ten years. Recently the subwoofer blew an internal fuse. A check with an old analog ohmmeter seemed to indicate the TIP31 (Q1) was shorted. I happily replaced it AND the TIP32 (Q5). It still blew fuses.
I then checked the bridge rectifier and it seems OK. I removed the two filter caps, C2 and C6, and checked them. They appeared OK, too.
Not knowing anything about FET transistors, I ordered a new pair for Q2 and Q7. With those two transistors out it didn't blow fuses. Then I checked the other transistors and the diodes with the ohmmeter. All appeared OK.
When the new transistors, Q2 and Q7 arrived, I replaced them and tried the amp again. It still blows fuses.
Then I pulled the bias jumper, 100con2, and tried it. It didn't blow the fuse and drew very little AC current.
Now I'm stumped and need help.
I then checked the bridge rectifier and it seems OK. I removed the two filter caps, C2 and C6, and checked them. They appeared OK, too.
Not knowing anything about FET transistors, I ordered a new pair for Q2 and Q7. With those two transistors out it didn't blow fuses. Then I checked the other transistors and the diodes with the ohmmeter. All appeared OK.
When the new transistors, Q2 and Q7 arrived, I replaced them and tried the amp again. It still blows fuses.
Then I pulled the bias jumper, 100con2, and tried it. It didn't blow the fuse and drew very little AC current.
Now I'm stumped and need help.
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