Blown JBL PX300.4 Amplifier?

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y2j514

Copper - Posts: 94

Joined: April 26, 2007

Location: Quebec, Canada

Posted: April 10, 2009 at 2:17 PM / IP Logged

Ok, so I have a JBL px300.4 amplifier (125 wattrs x4 rms), and I went to get a car wash the other day and my trunk must have leaked, and my amplifier stopped working, as soon as I realized it I immediately turned everything off. I took my amplifier apart and here is what I found to be the problem:

Blown JBL PX300.4 Amplifier? -- posted image.

So I was wondering - rather than buying a new amplifier, couldnt I just simply solder on replacement parts? I'm not sure what those are, but I think they're tiny capacitors...am I right? Where could I find replacment parts?

In case its not clear on the picture, the blue (capacitor?) that is blown up and hanging on by a thread says "(M)P", "85 DEGREESCELIUS", "U5E" (maybe micro 5E), and "16V"

Any help would be appreciated.

Thank you

i am an idiot

Platinum - Posts: 13,667

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: April 10, 2009 at 5:16 PM / IP Logged

What are the numbers on the other side of the cap. See the caps behind that one that say 16V 22micro F those are the numbers we need. When replacing them, it is very important that you notice the polarity of the cap. The board appears to have a + on the positive location. The cap will have the negative marked.

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: April 10, 2009 at 5:31 PM / IP Logged

Do not set the amp on carpet. There are MOSFET transistors in the amp. They are static sensitive, I have only heard of static taking one out. But they say it is possible.

y2j514

Copper - Posts: 94

Joined: April 26, 2007

Location: Quebec, Canada

Posted: April 10, 2009 at 5:35 PM / IP Logged

Its hard to tell because the plastic surrounding the cap melted, I believe it says 16V 10uf, but it might be 18uf. Im leaning more towards 10, because I grabbed a magnifying glass and took a look and I dont seem to see any sign of a horizontal line in the middle of the 0 to indicate an 8.

bwhvac065@aol.c

Copper - Posts: 67

Joined: April 05, 2009

Location: Indiana, United States

Posted: April 11, 2009 at 12:17 AM / IP Logged

hey i am an idiot yo said mosfet what is that and what does it mean? and what about sub box carpet? or does it have to be pos charged?

Blazerspl

6 rockford 12s

5500 watt pa amp

12.0 cubic enclosure

BIG 3

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haemphyst

Platinum - Posts: 5,054

This member has been recognized as an authority in Electrical Theory. Click here for more info.

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: April 11, 2009 at 1:12 AM / IP Logged

MOSFET - Metal Oxide Semiconductor Field Effect Transistor.

They are static sensitive when not referenced to a ground, such as the chassis or heat sink of the amplifier. While mounted in the chassis, they are (relatively) immune to static, but while out of the chassis, as this board is, a TINY static pop - one so small you can't even feel it - can damage them beyond use.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

bwhvac065@aol.c

Copper - Posts: 67

Joined: April 05, 2009

Location: Indiana, United States

Posted: April 11, 2009 at 1:17 AM / IP Logged

wow its amazing i wonder how often that sorta thing happens?

Blazerspl

6 rockford 12s

5500 watt pa amp

12.0 cubic enclosure

BIG 3

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: April 11, 2009 at 5:07 AM / IP Logged

When Rockford built the Power 650 in the mid 1980s, it was then interpreted by a bunch of fella's from Lake Charles, La. to stand for Made Of Something (Don't Remember what word goes here) Extra Terrestrial. But Haem's translation was right on the money.

I have tried to take one out with no luck. However I do know of one that was taken out by static. It must happen occasionally, the manufacturers take all kinds of precautions when shipping them.

y2j514

Copper - Posts: 94

Joined: April 26, 2007

Location: Quebec, Canada

Posted: April 17, 2009 at 12:56 PM / IP Logged

Ok, so I went to the local shop to buy some capacitors. It couldn't find the exact same capacitors, so I bought some that were rated at 16v, and 10 uf, but rather than 85 degrees C they're 105 degree celcius - i didn't think that would make a huge difference. I soldered them in and bolted everything back up. I now have a new problem!

The protecion light doesnt come on anymore, but as soon as I turn on the radio and the amplifier powers up I hear a humming noise coming from the amplifier. I looked at it, and the protection light is off, the power light is on, and the I-E/OPT light is flashing. After about 5-7 seconds the fuses blow (2x30amp) and the humming stops.

I turned everything off, replaced the fuses, turned the car on, without the HU in, and then rechecked the fuses - they were fine. So they blow pretty much when the amp powers up.

Any thoughts?

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: April 17, 2009 at 3:50 PM / IP Logged

Chances are it has shorted output transistors. If you have a meter and are willing to do a little footwork, I can help you get it repaired.

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