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Old 23rd October 2013, 05:05 PM   #1
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Default Rockford Fosgate Power T 400-4

Hello, everyone ,
Here again , with a new repair

Well, the first thing I've seen, when you open the lid, (it's all perfect , no one has touched anything ) is , like you have entered some kind of liquid into the amplifier , ( the plastic of the three leds, had oily debris ....) and also , in a corner of the chassis, where it has the screw hole , I also appreciated dried remnants of fluids , and corrosion ,,?

That has been , at first sight, when I connected , blue LED lit , as well , but very weakly , (almost not lit) LED orange protective ...

Connected audio input , a music signal , (MP3 )

When connecting the speaker to the front channels are silent , without the slightest sound of any kind ....

In the rear channels : on the left, with the gain level to near maximum , we must bring the ear to hear very little sound.
In law, great leap of the speaker cone , of course ! , I measured with the multimeter , and there is 24.42 volts ....

In the other channels , no appreciable voltage .

I have checked all the output MOSFET , and have not found any short or open , too, all the drivers that are below the mosfet , and I have not found one in poor condition.

Any clue of where to keep looking ?
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Old 23rd October 2013, 05:51 PM   #2
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Remove the outputs from the channel with 24v. Does that allow the other channels to function properly?
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Old 23rd October 2013, 09:49 PM   #3
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Thank you for answering me, Perry.

I pulled the two MOSFET output for the rear right channel (Q14 and Q15), but I still have 2.9 volts at the output ...
The other channels are dumb ..... (0,010 volts)

......???
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Old 25th October 2013, 08:49 PM   #4
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Connect a jumper across the speaker terminals for the dead channel. If there doesn't seem to be a problem with excessive current draw or overheating components, check the other channels for audio.
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Old 25th October 2013, 09:58 PM   #5
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I connected the bridge, as you have told me, (for ten minutes) but is not seen no change, does not heat anything, nor is there excessive consumption ..

The other channels are still not working, (dumb) despite having an audio signal present at the input, and the level of gain near maximum .....

weird?

Note: I have not installed the output MOSFET.
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Old 26th October 2013, 12:13 AM   #6
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Check the transistor shown in the attached image.
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Old 26th October 2013, 03:55 PM   #7
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I have checked the transistor, but I have not found evidence that has a short or is open ....

He contrasted the values ​​I have taken that transistor, with the values ​​of the same transistor side plate, and there is a minimal difference (more or less than 0.20 ..)

I have checked the values ​​of other transistors, with the plate next, and I found few differences ...

Yes, I found Q204 (labeled 2A) has a short between the base and the collector, and to check on other plates, also in short ... is this normal?
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Old 26th October 2013, 06:11 PM   #8
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I unsoldered the collector of Q204, to check if he was really short, but no, the transistor is well, then, I have contrasted with a new one that I have in my closet, and its measurement is correct ...

I have reinstalled the output MOSFET .... I reconnected, now at least, are no longer present the 24.40 volt output was in the rear right channel audio ... there is only: 2.94 volts .....

I'm lost ....
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Old 26th October 2013, 09:10 PM   #9
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#7:
That's normal for the differential amplifier that's used in most all of the Rockford full range amps.

#8, Have you checked all of the resistors on the driver board to confirm that they're within tolerance?
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Old 26th October 2013, 09:24 PM   #10
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thanks for the clarification,

I will check it as soon as possible, to see if I find some resistance bad ..

Last edited by josesony68; 26th October 2013 at 09:40 PM.
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