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Old 26th May 2012, 02:58 AM   #1
chipper is offline chipper  United States
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Default rockford fosgate punch 800a2 non working

Hello everyone! I got my self a nice project! A Rockford Fosgate punch 800a2 a amp I've dreamed of having of my own but it's not working.... When i apply power to B+ & GND just power no REM it puts my 10 amp power supply into protect so that indicates the power supply is shorted. I checked all 8 MTP75N05HD's and they measure a dead short on the sources. And on the sources i get a resistance of .715 on all 8 of the fets on the gates but the from drain to source they measure .000 and beeeeeeeep on my meter. I also checked the outputs IRF640s measure out fine in both channels and IRF9640s.

What could have cause the power supply to short?
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Old 26th May 2012, 06:31 AM   #2
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What is the resistance between legs 1 and 2 for all of the power supply FETs?
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Old 26th May 2012, 07:27 AM   #3
chipper is offline chipper  United States
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Actually it's something with the transformer there's a smd resistor near by some of the legs of transformer where if I touch it will arch or move it around arch. I believe that's made the fets seem as if they were shorted but the amp still powers on. I removed it from the heat sink and it powered right on! Put it back in the sink it still powers on but of I touch or move the transformer it arch. I'll get a picture of where it sparks at.

Is problem common on these amps?
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Old 27th May 2012, 08:16 AM   #4
chipper is offline chipper  United States
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There seems to be some arching under the transformer amp actually works fine both channels but when you pull, twist the transformer it makes like a small spark by two of the legs of the transformer near that smd resistor.
and the amp had a broken gain pot on i believe was the left channel when i tried adjust it it made the speaker act weird and almost blew my kenwood book shelf speaker and then a smd cap blew right by the speaker terminal. I thought i fried the amp by the smell of what burned but was a smd component that burned up. I replaced the gain pot now that channel plays good i can adjust it and everything but im wondering if that part is important or what? please get back to me as what i can do for the transformer thing.. Thanks
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Old 27th May 2012, 08:19 AM   #5
chipper is offline chipper  United States
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and i thought maybe something was so i reflowed some solder on the joints of the transformer where it made a spark but that still did nothing its somewhere on the windings.
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Old 27th May 2012, 08:36 AM   #6
chipper is offline chipper  United States
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see that resistor between the caps and transformer theres two of the legs of the transformer where it arches when you move it or twist it.
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Old 27th May 2012, 09:18 PM   #7
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Maybe you should remove the transformer. Then unwind it a little and put some heat shrink or something around the problem area then rewind and install it.
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Old 27th May 2012, 09:33 PM   #8
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If it's arcing where the terminal windings meet the rest of the windings, coat a piece of cardboard with adhesive and wedge it between the windings. The cardboard will insulate it and the adhesive will keep it in place.
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Old 27th May 2012, 10:13 PM   #9
chipper is offline chipper  United States
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Would it be worth it to remove it and repair as necessary? I mean it doesn't look like a lot to remove but I'm just wondering that's pretty much it needs for it to be completely working.
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