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Old 25th November 2011, 03:19 AM   #1
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Default Kicker ZX750.1 Makes Squealing sound when powered up

Ok I finally have a DC clamp meter and it pulls 8 to 10 amps at idle with no input signal or speaker connected , removed all the output mosfets and the squealing stopped, then checked them all twice with diode check and ohm check, found three oddball ohms readings on the IRF9640 mosfets under 1 megaohm so i replaced those , and put all the rest back in and the squealing is back anyone have any ideas?
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Old 25th November 2011, 03:22 AM   #2
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also the 3 yellow 2200uf capacitors by the power and ground connectors are getting hot
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Old 25th November 2011, 07:41 PM   #3
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does anyone know why this would be doing this and pulling excessive current at idle?
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Old 25th November 2011, 07:49 PM   #4
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Does it pull excessive current if you pull the rectifiers?

Do you have a scope?
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Old 25th November 2011, 09:55 PM   #5
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I do have a scope, and ill pull them and check
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Old 26th November 2011, 12:04 AM   #6
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it pulls 1.06 amps at idle with rectifiers removed which is normal
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Old 26th November 2011, 03:48 AM   #7
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Remove the output transistors, reinstall the rectifiers, solder a jumper between legs 1 and 2 of U11. Do you see a clean square wave on the gate pads of all of the output transistors.
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Old 26th November 2011, 04:31 PM   #8
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Click the image to open in full size.

this is the result on the gate pads
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Old 26th November 2011, 09:42 PM   #9
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Adjust the trigger level to see if you can get the scope to lock on the waveform. If it won't do it with DC coupling, switch to AC coupling and set the vertical amp to 2v/div.

That's the high-side FETs. Also check the low side FETs.
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Old 26th November 2011, 11:03 PM   #10
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Click the image to open in full size.

here you go
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