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Old 28th August 2007, 05:27 AM   #11
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
I'm not sure who made these amps but it was not Rockford. They don't even support the amps and could provide no information when I asked them for a schematic.

The semiconductors with metal tabs must be insulated from the aluminum heatsink. Generally, they use silicone insulators. You will need to replace the cardboard with a suitable insulator.

Which transstors were burned? You already showed photos of the power supply transistors. Were some of the output transistors damaged also? When the legs of the outputs break, they rarely burn. It's usually a clean break. When the power supply transistor fail, they often burn the third leg off.

When the first leg of the FETs breaks, it will allow the gate to charge (either internally or externally by the intermittently connected leg). When there is no way for the gate of the FET to be discharged, it can't be turnd off before the other FETs are turned on. This will cause the amp to fail. Sometimes it causes other transistors to fail and other times it causes the amp to go into protect.
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Old 31st August 2007, 10:11 AM   #12
diyAudio Member
Join Date: Nov 2005
Location: Ohio
Seriously Perry how did you focus that image that much?
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Old 31st August 2007, 03:31 PM   #13
diyAudio Member
Join Date: Aug 2007
its not the same pic, i took pics of the fets on the other side
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Old 31st August 2007, 07:51 PM   #14
diyAudio Member
Join Date: Aug 2007
i wanted to know how i can test my mosfets with a multimeter? im new at this and have no clue, also i pulled them out, i can test them without them being soldered to the board? what do i look for if there ok? only 4 burned and i need 8 to replace all them, but the shop only had 5 so i replaced the burned ones, put power to the amp and one of the FETs i replaced didnt smoke but it popped.
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Old 31st August 2007, 09:05 PM   #15
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
It was a joke. Even if I could have cleared it up, I could not have removed the clamps from the transistors.

You can't replace only 4 of the 8. When the power supply fails, it's VERY rare that any of the FETs will survive. Just because there is no physical damage, that doesn't mean they're undamaged.

Go to the section labeled "Checking Field Effect Transistors" on page 97 of my car audio site. It will tell you how to check the FETs.

When you power up the amp, you need to insert a 10 amp fuse in the B+ line. This will help save the new parts if there are other problems. You also need to have the power semiconductors (FETs, rectifiers, regulators...) clamped to the heatsink before applying power.

You may also have defective driver transistors and defective gate resistors. Those should be checked. I'm not sure but the transistors Q405, Q406, Q407 and Q408 may be the drivers. If so, there will be continuity between the first leg and the gate resistors. One pair of drivers will go to 4 gate resistors and then to the gates of 4 FETs. The other pair will go to the other 4 FETs (via another 4 gate resistors). The 'A' (KTA1023?) driver transistors are most likely to fail.
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