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Old 16th January 2017, 03:25 PM   #1
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Default jl1000/1

The power supply of this amp is not working properly. the power supply mosfets (IRF3710) are reading as fallow, one transistor reads 47 ohms from gate to ground for one shoulder and the transistor right next to it reads 310k ohms from gate to ground for the other shoulder. is the 47 ohms reading OK,
or the drive circuit may have a short?
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Old 16th January 2017, 08:25 PM   #2
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There are 4 banks of FETs. Measure from gate to source.

1/2 of the FETs are driven with a ground reference so they will read the gate resistor value from gate to ground. All in the bank should read the same.
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Old 16th January 2017, 10:51 PM   #3
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Half of the FETS are reading 47 ohms from gate to ground and the other half is reading 310k ohms from gate to ground. I'm going to work with the drive circuit.
Is the power supply drive circuit the one with the UC3525 chip in it?
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Old 16th January 2017, 10:59 PM   #4
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What you have is what you should read.

Yes. The 3525 drives the main supply.

Is R871 within tolerance?

Are all of the diodes behind it soldered into the board?
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Old 16th January 2017, 11:45 PM   #5
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R871 is OK. I follow the PWM signals from the UC3525 and they go to two yellow transformers then to 8 diodes (d812 through d19), some times there is signal at the output of the yellow transformers, and even at the gates of the power supply, but it goes ON and OFF every 2 seconds. can I pull out the diodes without damaging the power mosfets?
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Old 17th January 2017, 12:00 AM   #6
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You can check the diodes without removing them. I doubt that they're defective.

Do you read significant DC voltage across the speaker terminals as it tries to power up?
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Old 17th January 2017, 12:14 AM   #7
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No DC or AC at the speakers terminals, and all diode tested good.
I also noticed that the problem start right at the output of the UC3525 chip.
I just replaced UC3525, but still have the same problem.
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Old 17th January 2017, 12:35 AM   #8
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It could be that the amp is going into one of the protect modes. Are any of the LEDs other than the green LED lighting up on top of the amp?
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Old 17th January 2017, 02:02 AM   #9
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Yes, the low voltage.
I put up the voltage from 12.5 to 13.5, and now the amp is not going Off and On, unless
I increase the volume.
I'm using a 35amps power supply, I'm going to use a 140 amps power supply and see the outcome.
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Old 17th January 2017, 03:02 AM   #10
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The amp tested ok with 12.5 amps volts at 140 amps, but don't work ok with the 12.5 volts at 35 amps?
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