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Rockford Fosgate M400-4D
Rockford Fosgate M400-4D
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Old 5th August 2017, 03:31 PM   #1
josesony68 is offline josesony68  Spain
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Default Rockford Fosgate M400-4D

Hi guys
Today I received this amplifier to repair, in which "someone" has put his hands to try to repair it ...
As you can see in the first photo, five electrolytic capacitors were completely loose from the motherboard (these capacitors had lost their capacity and are swollen)
There are also some components that have been replaced by other dubious features ...

All the base plate is covered with a special varnish, which makes it difficult to read almost all components ...

Does anyone know of a scheme?
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Old 12th August 2017, 03:42 PM   #2
josesony68 is offline josesony68  Spain
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Well,

I have managed to run the power supply, I have replaced the damaged capacitors, and two resistors that were open, the rail voltage is present (49 volts).

When the amplifier is connected and signal is applied to the input, nothing happens, no sound appears.
The voltage at the audio output terminals is 0, 65 v.

I have checked all output FETS without finding anything strange, I have also checked if there is voltage supply in the preamplifier card (12.53 v are present).
Is rare...
I am a little lost, in this type of amplifiers by its condition and typology (new class D)

Does anyone have any ideas?
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Old 12th August 2017, 11:59 PM   #3
ian33 is online now ian33
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What about the - 12 for the pre-amplifier is it present?

If you have a scope check for oscillation on the output FETs
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Old 13th August 2017, 05:33 PM   #4
josesony68 is offline josesony68  Spain
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Thanks for answering, ian
-12v on the preamplifier board are present
In the audio output FETS (IRF842) there is no oscillation
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Old 14th August 2017, 02:25 AM   #5
ian33 is online now ian33
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I have an amp like this on the bench which is repaired already.The output FETs are IRFB4227

If you want to clarify any part number let me know.
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Old 15th August 2017, 12:38 PM   #6
josesony68 is offline josesony68  Spain
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Yes, the output FETs are IRFB4227, I had not looked at him correctly.

If I need to know anything, I'll let you know.

Thanks
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