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Old 09-27-2020, 10:38 PM   #11
khajr
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Join Date: Sep 2020
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Default Re: troubleshooting definitive technology prosub 60

Quote:
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
Yes. It’s Q7. Don’t know why I had Q4 in my head. All three pins on Q1 are shorted together. I will check speaker line voltage and the bridge rectifier. But I am going to guess the speaker line voltage is not going to be zero as it makes a hum.

My original replacement were the two mosfets, R19, the bridge rectifier, C2 C4. and the op amp. Would we still be concerned about the zener diodes at all?

Last edited by khajr; 09-27-2020 at 10:46 PM..
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