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Old 09-30-2020, 11:27 AM   #20
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Join Date: Sep 2020
City & State: Lexington, KY
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Default Re: troubleshooting definitive technology prosub 60

Originally Posted by R_J View Post
If the drive to the mosfets is bad, then the mosfets will be turned on, when they are turned on they will act as a short. If the circuit is working, the mosfets will be turned OFF and only turn on with the audio signal, basically Q1 and Q7 will alternate turning on and off according to the audio signal, and the voltage on the speaker will vary +/- producing the audio.
You need to be very careful working with these double sided boards, If you remove a through hole component and destroy the feed through, you will no longer have the circuit connection between one side and the other.
I tested to voltage at the connections for the mosfets and found the following:

P1 and P2 = +169V
P2 and P3 = -169V
P1 and P3 = -300mV

P1 and P2 = +163V
P2 and P3 = -169V
P1 and P3 = -6V

I will try and figure what they should be.
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