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Old 16th May 2012, 05:01 PM   #1
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Join Date: May 2012
Location: Baltimore
Default 300/4 parts?

Very new but I'm liking this forum. I've been DIY for 20 years with car audio and always been lucky that my dad is an old school audio repair man, until we ran into JL Audio's amp.

Is there anywhere someone can buy parts or does he have to go to the transistor level to fix my amp?

My dad described what he thinks is either a pre-stage for one channel or possibly a protection circuit that has two bad tansistors on it.

His thought was maybe the board is replaceable (and my preference as I don't want substitute parts if possible) - if not he can do the transistors if necessary but they are tiny surface mounts that are burnt.

When I call around locally I'm told all JL's have to go back to them for repair?

The board part number is EFB-076-81 - any help is appreciated. If it has to be the transistors - then we'll look them up, we do have three more boards just like it in the amp - but wanted to try it without having to unsolder those tiny little parts. Thanks gents.

BTW the good folks over at diycaraudio recommended here as they said "Perry" was out of this world with help. Also bear with me, I only listen and install them, my dad (who is 72yrs old BTW) is the repairman so if I said it wrong please don't kill the messenger - I also know how to post on forums and he doesn't.

Last edited by kspraker; 16th May 2012 at 05:18 PM. Reason: Additional info
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Old 16th May 2012, 06:21 PM   #2
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JL will offer absolutely no help as far as I have heard. Someone please correct me if this is not correct.

You will have to replace the transistors. Are they the two transistors near the top left corner?

Last edited by Perry Babin; 16th May 2012 at 06:27 PM.
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Old 18th May 2012, 11:45 AM   #3
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If I remember correctly they were near the top of the board (opposite side of where the board connects to the main board) and about 1/3 of the way across the board, but honestly once my dad had it apart I'm not sure of the orientation. I'll tell him to just replace them and test and see where end up, thanks for the assistance! I'll report back the results.
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Old 18th May 2012, 02:50 PM   #4
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I just spoke to my dad and says he thinks they are "NPN" but he's not sure exactly what type and he said it is important the put the same type back in functionality. If this isn't helpful - please ignore. I've asked him send me some pics of the board and failed parts.
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Old 18th May 2012, 05:20 PM   #5
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http://www.bcae1.com/temp/jlaudioboardx.jpg

The two in the image above marked A and B are BC850Cs, if I'm not mistaken. You should use the same part and you need to replace both of them.
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Old 22nd May 2012, 06:03 PM   #6
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Thanks again, sorry for the slow replies - dealing with two retired folks who don't even like checking email so I have to verify the picture was even seen before I reply. Thanks though - I'll keep you in the loop.
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Old 23rd May 2012, 06:10 PM   #7
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Okay from this picture just below Q3 and even with (to the left of) Q5 is a transistor marked "F3" - however on my board it is marked "F3O" - that is what is bad. As well is the resistor to the left of it marked with 2000 or 200O (which my dad believes to be a 200ohm resistor as measured from the other boards). So the transistor is the part he needs, he's reasonably sure he has the resistor already. Any input is appreciated!!
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Old 24th May 2012, 11:25 AM   #8
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Google smd code book, should have a translation for that part number.
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Old 24th May 2012, 12:49 PM   #9
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F3 is a diode, not a transistor. It's likely a 1SS193. You can look up the datasheet for it.
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Old 29th May 2012, 06:40 PM   #10
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Thanks so much for the help but my dad is now worried as he's found other bad parts on the board too and doesn't want to just start replacing parts and blow them up again if he hasn't found them all. He wants me to find a working board and just replace the whole board - so on to hunt down a broken down 300/4 for cheap for parts.
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