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Old 30th December 2012, 02:22 AM   #1
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Default KX1200.1 in repair

iv replaced all eight Power supply fets, checked all resistance before replacing and after.

now for the weird thing.. before i replaced the the fets the board would power up and relay would click(with the only fet that survived out of the eight that were in it when it went up. i tested it and it was very weak.)but i didnt get any sound well needless to say the two drivers were blown well i changed them and well it would still power up with the new ones. i didnt get any ac voltage on the transformer either times ,before or after the new drivers. well i figured it still didnt make enough ac voltage because it was running on one crappy fet, ordered me some 3205's from digikey (10 of them) always get a couple extra and extraordinary packaged chips arrived. now whats weird is after i installed all of the new fets, running on a 10 amp inline fuse. i powered it up and well it flop flops back and fourth power protect power protect about as fast as it took you to read the words. well it makes ac voltage on the transformer but its oscillating voltage and no voltage as fast as its going from power to protect.


im stumped. if anyone can give any ideas to check next.
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Old 30th December 2012, 02:38 AM   #2
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With the black probe on the negative speaker terminal and the red on the output filter inductor, do you read more than a fraction of a volt of DC?
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Old 30th December 2012, 03:00 AM   #3
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i will have to check monday. its at my shop. what if i dont? what if i do? what would that mean.
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Old 31st December 2012, 02:49 PM   #4
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ok. it stopped going back and fourth on protect and power now but it stays in protect. any ideas. and i get no dc voltage between -speaker and output filter inductor.
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Old 31st December 2012, 04:18 PM   #5
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ok. i replaced the drive transisters with new ones again. im getting =20vdc at speaker - and output filter inductor
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Old 31st December 2012, 04:20 PM   #6
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oscillating voltage between -20vdc and -0vdc.
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Old 31st December 2012, 04:24 PM   #7
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and im getting 8vdc on the case. weird
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Old 31st December 2012, 07:00 PM   #8
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Well if your getting any voltage on the case, you might have a transistor or rectifier somewhere that has punctured the insulator tape betwween itself and the case.
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Old 31st December 2012, 07:22 PM   #9
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Does this amp have a green board or a red board?
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Old 31st December 2012, 07:42 PM   #10
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red board. 04KX1200.1 i took all the power fets out and powered up fine. protect lights then it fades to power and relay clicks. but if i put two fets in(one on each side) it goes back and fourth again. with the fets out i get 4.34vdc on the gate pads. but when i put the fets in it slowly fades up to 2.8v then back down to 0v and then back up.

with the two fets in, the fet on the power input side gets hot fast. they are 3205's from digikey. i also replaced the 100Ohm gate resistors with 47Ohm resistors. same problems though..
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