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Old 15th January 2010, 05:20 PM   #1
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Join Date: Sep 2006
Default rockford fosgate p4004

Im working on this amp and 2 of the outputs are toasted they are FQA28N15
Wondering if i can cross this to a different part no or do i need the orginal?
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Old 15th January 2010, 11:38 PM   #2
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I have no idea if somebody makes anything else compatible. Perry should know, I can tell you that the part is rated at 28 amps and 150 volts. It is an N channel device. The other half of the channel uses 36P15s. 36 amps, positive channel, 150 volts.
If it ain't broke Don't fix it
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Old 16th January 2010, 01:32 AM   #3
Dimon74 is offline Dimon74  United States
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If you can find, use FQA46N15 .They are working perfect in these Punch series
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Old 16th January 2010, 03:52 AM   #4
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Join Date: Jan 2010
Goto and you will find them for $1.95Ea. Also, I would not use any substitutes, especially when the original parts are available and easily obtained. This will insure that all channels are operating identically. I have never had much sucess using any substitutes, NTE, ECG, etc. Therefore I discontinued even attempting to do so many years ago. Also, if I remeber correctly, these transistors are soldered to the intermediate heatsink board. This is tricky to remove and reinstall them, but it can be done. If all else becomes too difficult, note the location numbers of at least one of the transistors and purchase the pair as a whole assembly from Rockfords parts dept. at 800-366-2349. Hope this helps......V
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Old 18th January 2010, 06:27 PM   #5
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Location: Wisconsin
Just a helpful hint when removing these from the mesha strip, watch the surface mount transistor and 3 pin header on the board. It will float off the pads when you are heating up the fet.
I have been using those black binder clips for heat sinks, used to hold papers together. I clip a couple of those on the mesha strip to keep heat away from everything else. Those also work great for the older model mesha as well, clip the other fets next to the one you are heating.

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Old 18th January 2010, 07:46 PM   #6
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Join Date: Jan 2009
Location: Iowa
I have repaired 2 of those, and as Professor V said, just go with the originals. All 4 channels will be identical. I have however used substitute rectifiers on the board. To remove the MEHSA strip on that amp, I found a small hotplate to work great. Much easier on that amp than the amps with ALL of the transistors on the same MEHSA strip.
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Old 18th January 2010, 08:39 PM   #7
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Ive repaired plently of theese amp among others. Ive found that replacing the fets and outputs on theese amps no problem and pretty easy to do. I went with the orginals every time i repaired them. Just thought this time i might be able to sub the part out to something else to get this kid who owns the amp off my back since he calls me 100 times a day and i have to order the parts and have 100 amps in front of his to fix

Last edited by mike49504; 18th January 2010 at 08:40 PM. Reason: mis spelled
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Old 27th January 2010, 04:27 PM   #8
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Join Date: Sep 2006
Ok i put new outputs in the channel that was shorted with the same part numbers. Also replaced the a56 and a06 in that channel. with the new outputs in the amp it draws excessive current. Wondering where i go from here? I also checked the emmitter resistors they test fine also
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Old 27th January 2010, 08:02 PM   #9
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Location: Louisiana
Did you turn the bias pot fully counter-clockwise to eliminate biasing as the problem??
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Old 28th January 2010, 12:45 AM   #10
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Yes turned it fully counter clockwise. As soon as i try to power it up the outputs in that channel get hot almost instantly
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