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Old 20th December 2009, 08:42 PM   #11
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Are you sure that the 540 isn't defective?

Are you sure there are no solder bridges? Clean the area thoroughly and look at it with a high power lighted magnifying glass.
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Old 6th January 2010, 04:02 AM   #12
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Ok back to this amp it kept blowing the outputs in it everytime i replaced the bad one and the two beside it. I replaced all of the outputs, all the drivers,all the opamps, and a couple resistors and 2 caps.

My next question is should i check anything else in this amp before putting it back in the sink and powering it up?
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Old 6th January 2010, 04:22 AM   #13
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Do you have a 2 ohm current limiting resistor?
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Old 6th January 2010, 04:32 AM   #14
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i stopped over at my friends shop and all he had was a 1.8 ohm but i grabbed it from him
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Old 6th January 2010, 04:43 AM   #15
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With new outputs, drivers and fuses in the defective channel and all transistors clamped down. measure the DC voltage with the black probe on leg 3 of the outputs and the red probe on leg 1 of the same output. Do this for all 6 in the defective channel and post the voltages.

Of course, have the current limiting resistor in the B+ line.
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Old 6th January 2010, 05:08 AM   #16
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i couldnt test them all but the ones i did test read - 3.54 between legs 1 and 3

The reason i didnt test them all is because the 1.8 ohm 5 watt current limiting resistor got so hot it was smoking like crazy

Last edited by mike49504; 6th January 2010 at 05:08 AM. Reason: spelled wrong
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Old 6th January 2010, 05:10 AM   #17
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Test a few at a time. Let the resistor cool in between.

Did you set the bias fully counter-clockwise after replacing the outputs and drivers?
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Old 6th January 2010, 05:18 AM   #18
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irf540 0 volts between legs 1 and 3 . 9540 1.65 between 1 and 3

other channels 540 - 3.54 9540= 2.70

Havent turned any bias pots down which ones are they in this amp?
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Old 6th January 2010, 05:27 AM   #19
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The two circled in the photo and the other two in that area (didn't have a photo showing all 4). Turn the one nearest the channel that's failed.
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File Type: jpg IMG_7916x.jpg (141.7 KB, 81 views)
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Old 6th January 2010, 05:28 AM   #20
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Has the same output in one particular location failed repeatedly?
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