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Old 19th November 2012, 08:15 AM   #1
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Default Faulty Rockford Fosgate T8002

Slightly old thread but here it goes:
Would it be worth fixing this thing up?
All the output devices are fried, those marked with red. Only the ones on the left vertical side are ok.
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Old 19th November 2012, 02:09 PM   #2
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It's likely that only one the marked transistors is shorted. Measure the resistance from leg 1 to leg 2 for each transistor. If only one has lower resistance than the others. cut at least 2 of its legs free from the board and re-check the rest to see if any appear to be shorted.

If none of the remaining transistors appear to be shorted, install a 15-20 amp fuse in the B+ line to see if it will power up and produce clean audio.

If you have clean audio, it's likely that the drive circuit is OK.

You'll need to carefully check the gate resistor and the 0.1 ohm source resistor for the shorted transistor. Post your findings for this.

All of the marked transistors will have to be replaced.
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Old 20th November 2012, 03:37 PM   #3
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i don't see the red markings on the outputs, but do see the one missing from the circuit, which might be normal for this model. the mehsa board with the red dots is a part of the power supply circuit. also, what is going on with that cap by the fuse?
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Old 26th November 2012, 11:02 AM   #4
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3 pieces at the right hand side even got a hole burned in the casing. I checked them all using a dmm on diode testing as I always do but did not desolder any one of them. The fuse has severe discoloration from heat so I guess previous owner abused this amp over a long period of time.
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Old 26th November 2012, 05:57 PM   #5
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You need to give board locations when saying "pieces" in other words look at the silk screen on the board itself and say for example.....Q25,Q26,Q27 have holes burned in them.
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Old 26th November 2012, 08:59 PM   #6
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Yup but its on my desk at work so I better not start to disassemble it during work hours and posting at diyaudio. Lol
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Old 27th November 2012, 09:44 AM   #7
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Ok I understand, are you going to bring it home and further troubleshoot?
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