JL Audio 300/4 Low Audio Output Troubleshooting Tip

kds9591 · 25th December 2012, 05:03 AM

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.

jordan_ciaramit · 25th December 2012, 05:52 AM

Thanks for the info and picture....Good catch!

Perry Babin · 25th December 2012, 12:11 PM

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.

kds9591 · 25th December 2012, 01:09 PM

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.

25th December 2012, 05:52 AM	#2
jordan_ciaramit diyAudio Member Join Date: Oct 2006 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.

25th December 2012, 12:11 PM	#3
Perry Babin diyAudio Member 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. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

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25th December 2012, 01:09 PM	#4
kds9591 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.