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Old 09-26-2020, 02:11 PM   #1
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Join Date: Sep 2020
City & State: Lexington, KY
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Default troubleshooting definitive technology prosub 60


My prosub 60 is blowing fuses. I bought replacement 1.25 amp 125v/250v slo blo fuses. When I replace the fuse it blows immediately along with a loud buzzing/hum from the sub. Attached are the schematics from definitive technology. There was one bad resistor, R19, and I have replaced this with the correct 1/2watt 1ohm resistor. When I plugged the unit it that resistor pops and the fuse blows. I have also replaced the following: caps C2 and C4, the bridge rectifier D1, op amp U1D, and the power mosfets Q1 and Q7. I have also checked R18, R20, and R21 and they checkout fine (removed from board to check). I have also checked power thermistor R7 and it came back 17 ohms. I removed Z1 and Z4 and checked them and they read a 0.7 drop. I have also verified the subwoofer is viable per def tech by checking the resistance across + and - and it reads 59 ohms. It is supposed to be +/- 15% from 64 ohms. I have also gently applied even pressure on the sub and it moves without any noises. I am at a loss now. Anyone have any thoughts?

I should mention that this happens w/o the amp being connected to the receiver.

Thanks in advance.
Attached Files
File Type: pdf hightlevelamp.pdf (48.0 KB, 16 views)
File Type: pdf lowlevelamp.pdf (59.0 KB, 11 views)

Last edited by khajr; 09-26-2020 at 03:40 PM..
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