Jl Audio 300/4 Troubleshooting Tip - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th May 2011, 03:30 AM   #1
kds9591 is offline kds9591  United States
diyAudio Member
 
Join Date: Apr 2008
Location: Bensalem, PA
Default Jl Audio 300/4 Troubleshooting Tip



Worked on 2 of these JL Audio 300/4 4 channel amps last week with similar problems on the driver boards. ( On these boards the component #'s are not silk screened on the PCB.)

The first amp had a very low output on one channel. The problem was found to be a very, very fine hairline crack in the solder joint for the upper one of the 2 47K ohm SMD resisters on the board.

The other amp had no output on one channel and the bias current was not adjustable. The problem was found to be the lower 47K ohm SMD resister- the plating had separated from the resister. This was NOT visible even under high magnification.
Attached Images
File Type: jpg IMG_1733.jpg (868.3 KB, 164 views)
  Reply With Quote
Old 26th May 2011, 11:51 AM   #2
ppia600 is offline ppia600  United States
diyAudio Member
 
Join Date: Jun 2007
Location: Louis y ana
Good find
__________________
Don't worry... you can always turn the gain down!
  Reply With Quote
Old 26th May 2011, 01:30 PM   #3
Boofers is offline Boofers  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Ontario
Blog Entries: 1
Interesting, thanks for sharing.
  Reply With Quote
Old 31st May 2011, 01:42 PM   #4
amptech is offline amptech  Scotland
diyAudio Member
 
Join Date: Jan 2009
Location: Glasgow
Send a message via MSN to amptech
Hello there, I've seen many car amps over the years from burnt pcb's etc..the last one came to me rattling and not powering up due to being bolted to the sub box this is a no no. I would agree there circuit board cracks will make the unit cut in and out...

keep amp away from the bass box well not bolted to it any...lol

even easer this chap would to use his amp in the house so I rigged him up a 750w atx power supply unit to run it on..
  Reply With Quote
Old 3rd August 2014, 02:27 AM   #5
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
Quote:
Originally Posted by kds9591 View Post

Worked on 2 of these JL Audio 300/4 4 channel amps last week with similar problems on the driver boards. ( On these boards the component #'s are not silk screened on the PCB.)

The first amp had a very low output on one channel. The problem was found to be a very, very fine hairline crack in the solder joint for the upper one of the 2 47K ohm SMD resisters on the board.

The other amp had no output on one channel and the bias current was not adjustable. The problem was found to be the lower 47K ohm SMD resister- the plating had separated from the resister. This was NOT visible even under high magnification.
When you mention that the bias current was not adjustable was it stuck at 0 volts or around .45 volts? I've got a driver board that is giving me fits. I would like to fix if I could ever track down the problem. I've removed and swapped out the 47k resistors with no luck...
  Reply With Quote
Old 3rd August 2014, 05:48 AM   #6
diyAudio Member
 
lazzer408's Avatar
 
Join Date: Sep 2010
Location: Chicago
SMT+Amplifier=FAIL
  Reply With Quote
Old 3rd August 2014, 11:54 AM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
SMD isn't the issue. These resistors operate at very high temperatures. In time, the solder breaks down. That leads to even more heating and the resistors fail (lead terminal delaminates).
  Reply With Quote
Old 3rd August 2014, 11:55 AM   #8
diyAudio Member
 
Join Date: Feb 2014
Location: ohio
Those boards get fairly warm and often have resistor issues.Most common issue I've seen is transistor failure(differential pair).The two smd transistors in upper left corner beside the two resistors(102).
  Reply With Quote
Old 3rd August 2014, 02:22 PM   #9
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
So a good starting point with this driver board would be replacement of all resistors? I've looked at them all with magnification and probed point to point on virtually every connection on the board and it seems to have no issue until its installed in the amp. Then the issue is intermittent.

I've narrowed it down to the driver board because I swapped a new on into the amp I pulled this one from and the amp works fine now.

Would it be suitable to pull the outputs on the channel, let it be shorted and probe around to find where the voltages go astray in hopes to try and isolate the component/s causing the issue?
  Reply With Quote
Old 3rd August 2014, 02:30 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Have you tried comparing the voltages on each terminal of each component on a good board and a bad board? That may help lead you to the defective component in the circuit.

re post #8:
For those who find a defective differential amp transistor, both differential amp transistors must be replaced with matched transistors (same production batch is close enough). Having a mismatched pair can result in various problems but most commonly excessive DC offset.

to kds9591:
If you feel that some of these posts are too far off topic, have a moderator either delete them or move them to a new thread.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
JL Audio 300/4 Dr Zeus Car Audio 1 11th April 2011 10:43 PM
JL Audio 10w6v2 or Infinity Kappa 100.3se? Audison SRX4 or Jl 300/4? DcMaN Subwoofers 1 17th September 2010 10:28 AM
Help to repair JL audio 300/2 Solosound Car Audio 42 20th March 2009 12:52 AM
JL Audio 300/4 PQatPIT Car Audio 5 4th March 2009 02:06 PM
jl audio 300 2 ppia600 Car Audio 2 6th April 2008 03:54 PM


New To Site? Need Help?

All times are GMT. The time now is 04:42 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2