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Blown JBL PX300.4 Amplifier?


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i am an idiot 
Platinum - Posts: 13,679
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 19, 2009 at 2:16 PM / IP Logged  
I looked at your picture, they appear to be 47 ohm resistors.   The Z44s should work just fine in those locations.
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 19, 2009 at 6:14 PM / IP Logged  

Ok, so I have all the holes cleaned up - took some time.  Anyways - one of the pads on the bottom of the board lifted.  It was the middle pad, of where the fried transistor used to be.  I don't think its a huge deal because the pad on the top side is still sitting where it needs to be.  And I checked on an intact slot, and the bottom and top pads of left, middle, and right are continous with each other.  I still have the pads though - when we got to the point of putting in the Z44s, should i stick the pad back in there and solder over it?

Ok, so I'm going to go check the resistors in 5 minutes - I have 1 quick question.  You mentioned I need to connect the remote wire - does that mean when I test you want me to have the HU on, playing something?  Also - 5amp fuse ok, or should I put 30amp fuses in now?

i am an idiot 
Platinum - Posts: 13,679
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 19, 2009 at 6:28 PM / IP Logged  

Throw the pad away.  The connection is actually on the top of the board.  You want to solder that one from the top of board anyway. 

Radio needs to be on for remote power only.  No need to turn the volume up.  5 amp fuse is fine.

y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 19, 2009 at 7:05 PM / IP Logged  
Well good news is..nothing blew up. Bad news is...I can't get a reading.  I replaced the protection LED - so I cans see when it is in protection.  So when I turn the HU on, the amp goes into protection and the LED comes on - 3 seconds later that LED goes off, and the "power" led comes on...thats when I can get my readings at the resistors - except 2 seconds later the power LED turns off and the protection one comes on - a nice little cycle like that. So I tried to get readings at the resistors between cycles, but as the power comes on the voltage starts at 0 and climbs - its at 2.3~2.4 when the amp goes back into protection.  Im not sure if this is what you expected to happen - and those are the reading you want, or if we are getting cut off early.
i am an idiot 
Platinum - Posts: 13,679
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 19, 2009 at 7:23 PM / IP Logged  

The amp can not come on.  It has no power supply.  Are the 2 resistors near the exploded transistor acting exactly as the other 6 resistors?    The LEDs in that amp may work off of remote power.

It is not going to be a real big deal if you can not get the readings.  Do you have an old sealed beam headlight laying around?  We can use it for a current limiting resistor when attempting to power the amp up.  If there is a problem, we can find out without burning anything up.

y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 19, 2009 at 10:38 PM / IP Logged  

Ok, well I just looked at them - and I noticed that all of them osscilated between 0 and roughly 2.5 V.  However, one of them remained at a constant 12.2 V - exactly what my distribution leading the the amp read - so theres obviously no power regulating going on there.  The one right next to it osccilated between 0 and roughly 3.5-4 V.  So I figured aha! there it is...but when I brought it back inside I realized this is not the resistors next to the blown transistor - it is the ones on the opposite side - the side which initially had the folded Sil-pad.  So it didn't add up - so I figured maybe I screwed up it was dark outside - I'll retest again tomorrow morning.

As far as an old sealed beam headlight goes I do not have one - but I have my laptop power supply which is 19V at 3.2 amps - could we just use this as a power supply instead?  I know the voltage is a little high - but the amperage is almost zilch.

i am an idiot 
Platinum - Posts: 13,679
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 20, 2009 at 9:10 AM / IP Logged  
No do not use your laptop supply.
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 20, 2009 at 11:04 AM / IP Logged  

Do not worry - I wont do anything without you first saying that is what must be done.

Ok so I re-tested everything this morning in the light and it appears I did not screw up - here are the results of the DCV test:

Blown JBL PX300.4 Amplifier? - Page 6 -- posted image.

-A few notes to keep in mind.  The blown transistor was the one on the bottom right.

-I measured the voltage at both ends of the resistors because I got diffrent results depending on the end I used - so I figured that could be useful.
-Another perhaps useful tidbit of information is that in each row of 4 transistors/resitors, there are 2 resistors not associated with any of the transistors.  I decided to measure them for the hell of it...the 2 on the bottom measured normally (ie. fluctuated from 0-1.8 or so).  The 2 on the top read 0.0V at all times.....

i am an idiot 
Platinum - Posts: 13,679
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 20, 2009 at 8:59 PM / IP Logged  
I need to know if the resistor that was connected to the exploded transistor is connected to the top left power supply transistor.  Not the ends connected to the transistor, but the ends of the resistors nearest the center of the board.  I think you have a defective driver transistor.  If those resistors read near 0 Ohms when checking as described above, follow the trace on the bottom of the board, it goes through a feed through and ends up on top of the board.  It should go directly to a small transistor.  It may go to a second transistor also.  I need the number of both.  2SC and a 2SA numbers possibly.  DO NOT remove them I just need the number.
y2j514 
Copper - Posts: 94
Copper spacespace
Joined: April 26, 2007
Location: Quebec, Canada
Posted: April 20, 2009 at 10:07 PM / IP Logged  

Will check when I get home - but like I said the 2 resistors that read 0 are not ones directly connected to transistors...they are the ones u see inbetween the transistors.  Also - the exploded transistor is on the bottom of the board in that picture, and the zero reading resistors are on top. Anyways - I will check and get back to you.

Thanks for all the help btw - it is much appreciated.

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