Needing help fixing my amp please

jimcarrier · 12th March 2011, 12:19 AM

hi, here is the story, i've got a used jbl 300.4 car audio amplifier, it was broken, so i asked someone to repair it,

but now after 120 $ the amp is still dead.

here his what it do,

when i conect the power all inpuit/ output unpluged, the protec led light on, and 2 sec later the power led light for half a second, and then its restart...

and again and again and again ....

when the speaker are pluged i can hear some noise during the half second power.

can you help me fixing it please,

thank

jim

jimcarrier · 12th March 2011, 02:09 AM

well i found a shorted small transistor, will try changing it !

jimcarrier · 12th March 2011, 03:09 PM

ok now its playing for 2 sec then restarting do the same with and witout speaker,

what should i check ?

Perry Babin · 12th March 2011, 10:12 PM

Which transistors was shorted?

Can you post a photo of the inside of the amp?

sdoom · 12th March 2011, 10:17 PM

sounds like you have broken/shorted output transitors. The protection circuit senses that and turns off the power supply, ater a second the power supply circuit resets itself , the protection circuit senses a short .... Do you have a multi-meter that can measure resistance or has a diode-tester included ?

jimcarrier · 13th March 2011, 12:14 PM

the transistor who was shorted was in the power amplifier section,

ya i've got one multimetter, i have looked for all the transistor and none seem to be bad but i found a burned resistor in the power amplifier, maybe this is the onjly problême,

just for fun how do i test diode %?.

Perry Babin · 14th March 2011, 04:20 AM

What's the exact model number of the amp?

What is the part number on the face of the transistor?

jimcarrier · 15th March 2011, 10:07 AM

jbl px.300.4, and for the transistor i dont remember but i replaced with the same,

12th March 2011, 12:19 AM	#1
jimcarrier diyAudio Member Join Date: Mar 2011	Needing help fixing my amp please hi, here is the story, i've got a used jbl 300.4 car audio amplifier, it was broken, so i asked someone to repair it, but now after 120 $ the amp is still dead. here his what it do, when i conect the power all inpuit/ output unpluged, the protec led light on, and 2 sec later the power led light for half a second, and then its restart... and again and again and again .... when the speaker are pluged i can hear some noise during the half second power. can you help me fixing it please, thank jim

12th March 2011, 10:12 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Which transistors was shorted? Can you post a photo of the inside of the amp? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

14th March 2011, 04:20 AM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	What's the exact model number of the amp? What is the part number on the face of the transistor? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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12th March 2011, 02:09 AM	#2
jimcarrier diyAudio Member Join Date: Mar 2011	well i found a shorted small transistor, will try changing it !

12th March 2011, 03:09 PM	#3
jimcarrier diyAudio Member Join Date: Mar 2011	ok now its playing for 2 sec then restarting do the same with and witout speaker, what should i check ?

12th March 2011, 10:17 PM	#5
sdoom diyAudio Member Join Date: Mar 2004 Location: Heidelberg	sounds like you have broken/shorted output transitors. The protection circuit senses that and turns off the power supply, ater a second the power supply circuit resets itself , the protection circuit senses a short .... Do you have a multi-meter that can measure resistance or has a diode-tester included ?

13th March 2011, 12:14 PM	#6
jimcarrier diyAudio Member Join Date: Mar 2011	the transistor who was shorted was in the power amplifier section, ya i've got one multimetter, i have looked for all the transistor and none seem to be bad but i found a burned resistor in the power amplifier, maybe this is the onjly problême, just for fun how do i test diode %?.

15th March 2011, 10:07 AM	#8
jimcarrier diyAudio Member Join Date: Mar 2011	jbl px.300.4, and for the transistor i dont remember but i replaced with the same,

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