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Old 1st February 2014, 03:42 PM   #1
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Default old massive amp

I got this amp for repair, and it was drawing too much current. There are 4 driver modules and each driver module drives 6 fets, 4 x IRF9640 and two defaced fets.
Does anyone knows what fets are those?

Its a D 400X model.
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Last edited by ultra; 1st February 2014 at 06:38 PM.
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Old 1st February 2014, 03:45 PM   #2
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Make and model could be useful.
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Old 1st February 2014, 07:46 PM   #3
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They appear to be in circuit with the 9640's so I would assume they are 9640's or subs that their part # got scratched off. It was repaired, as you can see they used a RED dot on those two fets. They should of replaced all the fets instead of just two.
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Old 1st February 2014, 11:53 PM   #4
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The red dot was done by me in order to track their position. The remaining good defaced fets test as N ch in my component tester.
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Old 2nd February 2014, 07:45 PM   #5
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Seems it shouldn't have 4 p channel and 2 n channel. Should be 3 and 3. Someone scratching out part numbers is a sign of some seriously shady work. Generally the use of irfp9640 would be paired with irfp640. But then again from the looks of the pc board all the drains appear to be connected together, indicating they are all the same. Either way it looks like its not gonna be fun, good luck.

Last edited by jerluwoo; 2nd February 2014 at 07:50 PM.
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Old 4th February 2014, 04:42 PM   #6
tiomilo is offline tiomilo  Costa Rica
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i have seen some class D amps with 3 P channel mosfets and 2 N channel looks like yours have 4 P and maybe 2 N channel, but only need to measure Voltage @ source pin #3 if it is a classic class D build Korean design should be Vcc+- at IRF9640 and Vcc- at mystery ones presuming those are IRF640 N channel mosfets. source pin #2 should be output rail with their appropriate resistors.
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Old 4th February 2014, 06:48 PM   #7
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I confirm the amp works fine, even without one bank of fets.
I also confirm there are hi and low side pulses on each bank.
All i need to do now is to find the part number of the N fets, or else i have to replace them in all 4 banks (say with IRF640), that is 8 fets in total.
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