JL Audio 500/1 high dc voltage between sink and rca jack. - diyAudio
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Old 4th December 2012, 11:21 PM   #1
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Question JL Audio 500/1 high dc voltage between sink and rca jack.

I bought this amp on ebay as non working. Got it with only 6 screws holding the thing together. So i went to my local hardware shop and picked up a new set. I went ahead and cleaned the thermal compound and reapplied new between the black fins and the chassis.

I notice the amp has been repaired before because all the transistors have new solder. There are signs of blown fets in the power supply. Also only 2 gate resistors where replaced (smd ), don't know why they didn't replace all if them.



Well after powering the amplifier i got output. And after a few minutes of sine waves and a few bass tester tunes the amplifier was cold to the touch even after 30m of play. Then when i slightly wiggle the rca's to see if it was loose or had problems with i got i tiny shock. So i used my dmm and measure the voltage between the chassis and the rca's and i had 84.4vdc and -84.4vdc when i switch the test leads.


Any help appreciated.

Last edited by jeanious2011; 5th December 2012 at 12:37 AM. Reason: Swype text sucks.
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Old 5th December 2012, 12:40 AM   #2
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The only components that got warm where the rail caps and the transformers. But the heat sink was cold. My only guess would be a damaged mica insulator between a transistor and the sink, that's causing the voltage between the rca jack and the chassis.


The out put rcas don't have this problem, only the input.

Last edited by jeanious2011; 5th December 2012 at 12:44 AM.
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Old 5th December 2012, 12:40 AM   #3
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It sounds like you have either the rectifier or an output transistor shorted to the heatsink. With no power applied, see if you read 0 ohms between any of those components and the heatsink.
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Old 5th December 2012, 01:20 AM   #4
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I read 0 ohms between the ground, output rca's jack and chassis. Between the chassis and the input rca jacks i read 2m ohms.

I'll check the rectifiers and the output for any shorts.
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Old 6th December 2012, 01:12 AM   #5
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Sweet, Perry you are the man. Found out after removing the hold down clips that the who ever repaired it left the output transistors mounted to high so their toxin the clips themselves. Will lower them and retest.


Any idea where i can find those clips?? Seems like whoever did the repairs couldn't keep up with small amount if screed and parts, go figure. They made a ghetto clip, lol.


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Old 6th December 2012, 01:16 AM   #6
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THESE work well enough. I don't have a source for the originals. You don't re-use them. When you have to remove them, simply tear them off with a pair of pliers.

Someone on the forum stated that they were available from audioQ (if I'm not mistaken).
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Old 6th December 2012, 03:56 AM   #7
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Woah that link has a minimum order of 100,000pcs, their cheap but that's because you would have to buy a boat load.

So you're saying that the original clips can't be re used? I would assume they loose spring/tension.

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Old 6th December 2012, 04:43 AM   #8
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The original clips can be re-used if properly removed. This was for missing or broken clips.

The last time I purchased them, I ordered and received 100pcs.
Octopart
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Old 6th December 2012, 04:54 AM   #9
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Sweet, i forgot about Octoparts search engine. I know i have to use that before asking you, sorry...totally forgot about it.
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Old 15th December 2012, 09:00 PM   #10
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working like new again. I removed the old insulators and used kapton with new compound. Tested and no problems, got 45.5v prior to clipping. Sweet can't wait to try it out in my vehicle.

Thanks Perry.
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