JL Audio 300/4 Low Audio Output Troubleshooting Tip - diyAudio
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Old 25th December 2012, 05:03 AM   #1
kds9591 is offline kds9591  United States
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Join Date: Apr 2008
Location: Bensalem, PA
Default JL Audio 300/4 Low Audio Output Troubleshooting Tip

Repaired a JL Audio 300/4 Ver1 series with very low audio output on all 4 channels. After some troubleshooting and voltage measurements found pin 3 of U600 on the daughter board had no voltage on it. Pin 3 usually measures approx 4VDC. Problem found to be a open trace connecting R612-R615 caused by a corroded via (plated through hole) had no continuity between top and bottom of brd. See picture.

Hope this info is of help to someone.
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File Type: jpg Open trace 300 4.JPG (196.2 KB, 105 views)
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Old 25th December 2012, 05:52 AM   #2
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Location: Franklin, Tn
Thanks for the info and picture....Good catch!
Tek 2221 scope with 2 10x probes, 2 Fluke 115 true rms meters. 106a, 20a & 5a power supplies. I have read the BCAE scope page.
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Old 25th December 2012, 12:11 PM   #3
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Join Date: Nov 2003
Location: Louisiana
This is a common problem on JL amps. It always seems to happen near the power/ground terminals. Green corrosion in the vias is a sign that there's a problem. There are almost always several that are near opening (either the pad around the via or the via itself). Many times, you need a high-power lighted magnifying glass to see the damaged (but still connected) traces.

THIS is another thread with a few photos showing the type of damage to look for.
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Old 25th December 2012, 01:09 PM   #4
kds9591 is offline kds9591  United States
diyAudio Member
Join Date: Apr 2008
Location: Bensalem, PA
I had 7 other corroded open via's I repaired on the same board including 2 under IC U600. I scraped the coating on the foil both sides to expose the copper, used a dental pick to open up the hole a bit and used 30 gauge buss wire to fill the hole. I used liquid flux to provide better flow through for the solder.

Between the Luxo lamp and a eyeloop I was able to see the corroded via's but some that looked good I found with a meter. I'll have to try that # 80 drill bit method you mentioned in the other JL Audio thread next time.
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