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Old 12th October 2007, 06:57 AM   #1
lalo01 is offline lalo01  United States
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Default kenwood kac8401 no power

Hello every body, am new in this forum, and this is the second time I tray to fix a car amplifier and no luck, right now am tray to fix my Kenwood kac-8401. I was working fine but two weeks ago stop working so I take it out of the car and I use a pc power supply just to test it and the red led turns on, so I did i research on the internet and I read that went that happens is because the amp is protect mode, so I open it and I did no fund any transistor mosfet burn, so I measured whit digital multimiter and I think I found two fets bad so I replace it and I test it again on pc power supply and no luck the blue led turns on but turns of right away, so I thut maybe there is more transistors bud and I replace four more on the same line and now no power the led tray to turn on but turns of rig away. I donít really know how to measure or test the transistors mosfet but I just notice that there is some deferent then the others, am getting crazy I really want to learn to fix my amp this is the second time that happens and I donít want to throw this amp again so if somebody know and want help me to fix this problem i will really appreciated
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Old 12th October 2007, 07:21 AM   #2
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Location: Dona paula, Goa
Connect a voltmeter(Multimeter) to the speaker terminals and then power the amp without the speakers.
Repeat it for each channel starting from 'Connect.... speakers.'
If one of the channel is faulty, u will read increasing dc voltage at the speaker terminals.
Then u will have to rectify that channel.

Other reason could be the faulty internal PSU.

Gajanan Phadte
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Old 12th October 2007, 03:22 PM   #3
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There should be two different size transistors. The larger ones will be the output transistors. Measure the resistance between the second and third legs of each individual transistor. If you find any that read near 0 ohms, they need to be removed and checked. If they still read near 0 ohms, they are defective.
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Old 12th October 2007, 06:26 PM   #4
shagone is offline shagone  United States
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lalo01 i just sent you an email. i hope i can help you out.
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Old 16th October 2007, 04:52 AM   #5
lalo01 is offline lalo01  United States
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am wander if any body know what it`s the order to place the transistors npn and pnp back in to the pcb like i tell you guys im in the lerning process and went i teke it out of the boar i did not put atencion and now i just dont know, same problem whit the diodes y have two i dont know what goes first . please help me
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Old 16th October 2007, 04:52 AM   #6
lalo01 is offline lalo01  United States
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Am tarrying to post pictures of the amp, but the web donít let me
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Old 16th October 2007, 05:04 AM   #7
shagone is offline shagone  United States
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sounds like you need a schematic. does anyone out there have a schematic for a kenwood kac8401 ? i may have a simmilar around to look at but pictures of yours would help.
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Old 17th October 2007, 04:01 AM   #8
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Location: Dona paula, Goa
If somebody tells a noob to remove this and that and test it, it is a totally wrong approach. I am sure the copper has already come off the laminate.

We seem to forget our first attempt at electronics and the mess and mistakes we made, and take things for granted after being experienced. This is where we miss things and the moderators are very good in explaining such details. I envy that.

It is not a big secret that u will explain on a pm but doing it on the open lets detailed- minded to give u a flawless advice and precautions.

Just a suggestion that is good for all.

Gajanan Phadte
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Old 17th October 2007, 05:57 AM   #9
shagone is offline shagone  United States
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i have offered the original poster to come by my place so that i can help him troubleshoot but i have not told him to remove anything yet. he did that on his own. any advice you can give him would still be of great help.
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Old 18th October 2007, 03:56 AM   #10
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Location: Dona paula, Goa
lalo01
Do u have a multimeter, what type -digital or analog.

What are the numbers of the transiators(3 lead devices) out of the circuit.

A picture or a sketch of the pcb.

Gajanan Phadte
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