Rockford fosgate punch 125.2 repair help - diyAudio
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Old 24th February 2012, 09:27 PM   #1
chipper is offline chipper  United States
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Default Rockford fosgate punch 125.2 repair help

I got here a punch 125.2 that had a blown power supply. I put in a pair of irf3205s. Amp now turns on but one channel was shorted I replaced with new irf540's & new irf9540's. After putting those in I power on the amp all it just does is put out DC and the other channel pushes the speaker in and out with loud high pitched sound. I measured the fets in both channels and they measure fine. I don't get what's going on. When I removed the bad fets in on the bad channel the good channel played music now it won't.

What's going on?

Board number is PC - 1884-B
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Old 24th February 2012, 09:58 PM   #2
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Desolder the new FETs in the blown channel. Does that allow the other channel to work as it did?
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Old 24th February 2012, 10:02 PM   #3
chipper is offline chipper  United States
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Never mind I think it's something with the RCA connections like if you move it around or when I put the cover on and put the alen screw underneath the RCA connection the channels will throw out dc and make high pitched noises. What's causing this? Lose connection or open trace?

Note: both channels actually play fine but if you touch the RCAs it will freak out and act weird.
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Old 24th February 2012, 10:13 PM   #4
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The RCA jacks with 4 or 6 jacks are known for broken shield ground connections. The break between the board and the jack.

Open traces are not likely because most traces are burned open and that causes a gap that cannot be reconnected by moving the jacks.

As a side note, I've never seen the RCA jacks cause the amp to produce DC. The output stage is AC coupled so it's isolated from any DC produced in the preamp section.
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Old 24th February 2012, 10:22 PM   #5
chipper is offline chipper  United States
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This one has one pair of RCA jacks for left & right. But if I move it around or anything it will make the speakers push in & out and make loud high pitched noises.

I thought something blew but it's something in the RCAs. Could it be a broken connnection between the board?
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Old 24th February 2012, 10:50 PM   #6
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http://www.bcae1.com/temp/rcajacks.swf
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Old 25th February 2012, 09:02 AM   #7
chipper is offline chipper  United States
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Is it normal for the transformer to run a little above warm?
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Old 25th February 2012, 11:47 AM   #8
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At idle, they generally operate near room temperature.
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Old 25th February 2012, 02:06 PM   #9
chipper is offline chipper  United States
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How about while playing music? But at 20% of volume with bass & treble controls all the up amp is on my bench connected to 8 ohm speakers one per channel.

For the RCA jacks I added a little solder to the solder joints I'm still not sure if it fixed it. I put the cover on with the hex screw and I guess it seems 'normal' to me had it playing for 45 minutes.

Oh my power supply is a small pyramid switching power supply of 10 amps constant out put at 13.8v
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Old 25th February 2012, 04:31 PM   #10
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You should have desoldered the jacks and removed them to check them. If this fault is causing DC to be applied to the speakers and you're confident that the RCA jacks are part of the problem, you need to make absolutely sure that they're not broken. If it happens in the vehicle, it could burn the voice coils on the speakers.
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