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Old 2nd October 2012, 05:21 PM   #1
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Default JL 500/1 distorted output

Anyone have a schematic for this thing? I have one that is driving me nuts. it had blown outputs, blown power supply transistors, etc..

replaced all that, replaced the driver transistors in the output stage, and replaced the power supply mosfets along with its driver transistors.

amp powers up now, but the audio is distorted. Checked the gate drives on the outputs and they look ok. i see PWM on all 4 gates.

But the output is really distorted, its not low. it can get loud but its distorted. I checked the speaker output with the scope, and it appears to have PWM on it too.

Someone also used IRF540A as outputs too.

any ideas?

Last edited by mbates14; 2nd October 2012 at 05:27 PM.
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Old 2nd October 2012, 06:14 PM   #2
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the square wave i see on the speaker output is 56.8Khz according to the scope, I pulled the filter output caps and tested those, they are ok. the 10w 10ohm resistor looks ok.

I am at a loss, someone come to the rescue. hehe,.
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Old 2nd October 2012, 07:08 PM   #3
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Q504 and Q507 appear to have no oscillation, there is no signal on the tabs, just an out-of-range positive voltage.

the inner-two have oscillation. appears to be a large square on the tabs.

the speaker terminals to ground is 15v. Rail voltage is about 71v.
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Old 2nd October 2012, 07:35 PM   #4
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nevermind, i fixed it. it was a dumbass moment of the day. I installed Q501 backwards and opened up R502 without any physical defects.

Replaced the R502 and swapped around Q501 and the amplifier now works fine. UGH..... Tired i guess.
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