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Blown JBL PX300.4 Amplifier?


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y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 17, 2009 at 9:36 PM / IP Logged  

When they arent touching it reads:

------------
| 1         |
------------

When the leads are touching it reads:

-----------
|     001|
-----------

Note the difference in alignment (left vs right).  When I get a reading it is alligned to the right, similar to when the leads are touching.

i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 17, 2009 at 10:00 PM / IP Logged  

The outputs appear to be fine.  See the 4 devices with no exposed metal on the back?  These are the rectifier diodes, One lead on middle leg, other lead to left then right leg.  Notice reading on both. 

y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 17, 2009 at 10:14 PM / IP Logged  
just to clarify - the 1 and the "*" on my last diagram were 1s and not 001s, as in similar to no connection, not leads touching.  I cant check the other ones right now, because I am not a home now.  But I will get to it asap and get back to you.  I appreciate all the help!
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 18, 2009 at 12:43 AM / IP Logged  

Here are the results from the next part - seems pretty consistent to me.

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 18, 2009 at 1:15 PM / IP Logged  
Those appear to be ok too.  When you took the amp apart, did you remove any rubber pads that went between the transistors and the heat sink? 
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 18, 2009 at 1:46 PM / IP Logged  

Between the transistors/circuit board and the casing it was bolted to, there is this long sort of film like material that has a rubbery feel to it: here are some pictures.

Here is just a quick "blow-up" view of the entire amp:

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

Here is the rubber I hope you were referring to:

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

Actually, I just noticed all that "burnt" looking stuff on the last picture right..........................here ^^^^^ looking at the picture now.  Relevant?

It is possible that when I put everything back together to test it that maybe one of the transistors didnt have the rubber thing between it, because when I pulled it out it was folded on itself near the end.

i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 18, 2009 at 2:44 PM / IP Logged  
If it was folded and one or more of the transistors were touching the heat sink, that is definitely your problem.  The hot spots on the bottom of the board are nothing to worry about.  But since you have the board out of the heat sink, it might be a good idea to add a little solder to the joints.  Chances are on the other side of the board, there are 2 high power resistors.  These are to drop the voltage for the preamp power supply.  It is normal for them to run a little hot. 
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 18, 2009 at 2:58 PM / IP Logged  
Ya you're right - there are resistors on the other end.  So you're saying - I should try putting everything back together again, paying close attention to the rubber strip and try again?  Looks like Im heading to good old canadian tire for some more fuses.  I only have mini ones left, this take ATO ones.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 18, 2009 at 3:53 PM / IP Logged  

Just to be safe, purchase a few 5 amp fuses too.  If you put the 5s in it and it still has a problem, the power supply should be very well protected.  If it powers up with the 5s, and does not blow them, all is fine and you can place the larger fuses in the amp.  Do not play it with the 5s, unless you have no other use for them.  It will not play loud with 5 amp fuses.  They are just to make sure there are no problems at power up.

y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 18, 2009 at 6:39 PM / IP Logged  

Ok, so I bolted it all back together - left the fuses out and hooked up the 12+ and ground, no RCAs, no speaker, no Remote signal from the HU.

The second I put in the fuse (I used 10a - didnt have any 5a lying around) I got a spark a bad smell and some smoke.  I immediately took it out disconnected the power and took it all back apart.  Here is whats up:

1) A Capacitor blew up again - another 16v 10uf one - I have the end that blew off, but I cant find where it came from on the circuit board

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

2) Out of the 3 separate devices in the back (the output transitors, the rectifier diodes, and the ones we didnt test - they look like rectifier dioder but have a metal backing.  Well the one we didnt test one fried big time.

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

3) The protection LED is broken ( I noticed this before applying the power)  I must have done it when manipulating it.  Any ideas what spec I would need on another LED to replace it?

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

So, I figured you would want me to redo pretty much everything that has been done so here it is:

Blown JBL PX300.4 Amplifier? - Page 3 -- posted image.

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