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Old 31st July 2012, 11:31 PM   #1
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Default ADS P840

I just got one of theese amps in for repair today..

The power supply fets are shorted along with a few outputs...

The amp has NDP7060's for the power supply fets ..

The gate resistors are 10 ohms The drivers are MPSA56 and 06

Wondering would the IRFZ48V's work in this amp If so do i need to switch the gate resistors or will the 10 ohm resistors work?

Last edited by S Merlington; 31st July 2012 at 11:37 PM.
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Old 31st July 2012, 11:52 PM   #2
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FDP70N06 or HUF75339P3 might be a better choice. I prefer to cross reference parts from the same manufacturer, that's me though. I wouldn't worry about the gate resistors.

I would note on the PCB or heatsink with a permanent marker what the originals were.
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Old 1st August 2012, 12:42 AM   #3
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IRF1010E
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Old 1st August 2012, 01:14 AM   #4
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I will have to order the 1010E's ..

For testing only can i stick the IRFZ48V's in this amp to see if there are any other faults?

If so would the 100 ohm gate resistors still be fine ?
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Old 1st August 2012, 02:25 AM   #5
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The 48V should be fine for testing, that's a 10ohm not 100 correct?

Gate resistors will be fine if they are 10 ohms.
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Old 1st August 2012, 07:52 PM   #6
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I thought i had some IRFZ48V's on hand but guess not.

I had some IRFZ44V's on hand just for testing i stuck them in..

With just power and ground hooked up no remote i put a 1 ohm 25 watt current limiter in series with the B+ and the amp draws excessive current..

I pulled the rectifiers in the amp and again only hooked power and ground to the amp Same thing it draws excessive current ..

All drivers are brand new and the gate signal looks perfect..

Any suggestions on where to check next?
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Old 2nd August 2012, 12:31 AM   #7
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Twist the transformer to see if the current draw changes.
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Old 2nd August 2012, 01:40 AM   #8
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Twisting the transformer makes no difference in current draw..

Someone has replaced the drivers at some point in this amp..

Just to make sure they are in the correct locations The collector of the MPSA56 would be connected to ground ??
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Old 2nd August 2012, 05:17 AM   #9
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The collector of the PNP transistor would connect to ground if this amp uses the most common type of drive circuit.
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Old 2nd August 2012, 07:52 PM   #10
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Anything else you can think of why it would draw excessive current with just power and ground hooked up if the drive circuit looks fine on the scope..

And if the transformer isnt bad
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