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Old 09-28-2020, 08:18 AM   #12
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Default Re: troubleshooting definitive technology prosub 60

Originally Posted by R_J View Post
R7 is a ntc thermistor, it gets hot and the resistance goes down, thats how it works. it will not be the problem. The cold temperature is 20Ω It is just for inrush protection. they can fail open but this one is working. The bridge rectifier is also likley ok, check if you have + & - 170 volts, this voltage is likely lower with the lamp in line. but both + & - voltages should be close to equal.
I see Q1 and Q4 (or should that be Q7) and R19 are quite hot, it could be that the mosfets are turned on hard.
What is the voltage on the speaker line? that needs to be near 0 volts
The + and - voltages on the bridge rectifier were off by an order of magnitude and the there was current through the speaker wire.
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