Rockford Fosgate T3002 no output

clayton · 15th February 2010, 12:19 AM

This amp was in my sons truck. He said it just quit putting out sound. The amp gets power with no protection light coming on. The amp is not pulling excessive current. So I pulled the cover off & checked the outputs. 2 of them are shorted, which are FQA28N15 board location q218 & q222. Also there are 2 transistors(I think that is what they are) that are also shorted. 1 of them has # lm317t board location q13, the other #lm337t board location q12. I did a search on Mouser but could not find them. What would be a good cross for these 2.
This amp is different from amps that I have worked on before. I am used to working on old school amps. So I am a little lost as to what what else I need to check. I would like to try & get this up and running asap, because he is supposed to be going to a comp show in a couple weeks. Any help would be great

Perry Babin · 15th February 2010, 01:22 AM

The 337 and 317 are regulators and only VERY rarely fail. Are you sure they're shorted?

They have low value resistors connected between the output and adjust legs which will make many meters produce a steady tone.

clayton · 15th February 2010, 02:16 AM

I tested the regulators again. On the 337 with neg probe on pin 2 & pos on pin 3 got 3k and started rising rapidly til 8.45k then slacked off to a slow rise. Same thing with pos on pin 1. On the 317 with pos on pin 3 started at 3k Rose rapidly to 120k. With pos on pin 120k constant. This is with them in circuit. Does this sound right?

Perry Babin · 15th February 2010, 02:26 AM

I've never tried to test them that way but they don't appear shorted. The T5002 regulator is attached. Yours should be similar.

clayton · 15th February 2010, 12:26 PM

Is there anything else that needs to be checked?

Perry Babin · 15th February 2010, 01:00 PM

Get the schematic diagram from Rockford, email me a copy and I'll tell you what else to check.

It's likely that only one of the 28N15s is shorted. Measure the resistance from leg 1 to leg 2. The one with the lowest resistance is the shorted one. Cut it out of the circuit and see if the amp will power up.

clayton · 16th February 2010, 02:46 AM

Rockford is closed today due to presidents day. Will contact them tomorrow and get schematics. The amp powers up fine, it just does not produce any sound. Should I still cut the legs, or were you thinking that it was not powering up.

Perry Babin · 16th February 2010, 03:07 AM

If they're shorted, I'd expect the amp to be going into protect mode.

Did you check them individually to see if only one was shorted?

Have you tried moving all of the controls through their entire range to see if the other channel produces any audio?

clayton · 16th February 2010, 04:15 AM

DO they need to be out of circuit to do the test?

Perry Babin · 16th February 2010, 04:18 AM

Did you check them individually to see if only one was shorted?

15th February 2010, 12:19 AM	#1
clayton diyAudio Member Join Date: Apr 2004 Location: LA.	Rockford Fosgate T3002 no output This amp was in my sons truck. He said it just quit putting out sound. The amp gets power with no protection light coming on. The amp is not pulling excessive current. So I pulled the cover off & checked the outputs. 2 of them are shorted, which are FQA28N15 board location q218 & q222. Also there are 2 transistors(I think that is what they are) that are also shorted. 1 of them has # lm317t board location q13, the other #lm337t board location q12. I did a search on Mouser but could not find them. What would be a good cross for these 2. This amp is different from amps that I have worked on before. I am used to working on old school amps. So I am a little lost as to what what else I need to check. I would like to try & get this up and running asap, because he is supposed to be going to a comp show in a couple weeks. Any help would be great

15th February 2010, 01:22 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The 337 and 317 are regulators and only VERY rarely fail. Are you sure they're shorted? They have low value resistors connected between the output and adjust legs which will make many meters produce a steady tone. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

15th February 2010, 01:00 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Get the schematic diagram from Rockford, email me a copy and I'll tell you what else to check. It's likely that only one of the 28N15s is shorted. Measure the resistance from leg 1 to leg 2. The one with the lowest resistance is the shorted one. Cut it out of the circuit and see if the amp will power up. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

16th February 2010, 03:07 AM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If they're shorted, I'd expect the amp to be going into protect mode. Did you check them individually to see if only one was shorted? Have you tried moving all of the controls through their entire range to see if the other channel produces any audio? __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

16th February 2010, 04:18 AM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you check them individually to see if only one was shorted? __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links


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15th February 2010, 02:16 AM	#3
clayton diyAudio Member Join Date: Apr 2004 Location: LA.	I tested the regulators again. On the 337 with neg probe on pin 2 & pos on pin 3 got 3k and started rising rapidly til 8.45k then slacked off to a slow rise. Same thing with pos on pin 1. On the 317 with pos on pin 3 started at 3k Rose rapidly to 120k. With pos on pin 120k constant. This is with them in circuit. Does this sound right?

15th February 2010, 12:26 PM	#5
clayton diyAudio Member Join Date: Apr 2004 Location: LA.	Is there anything else that needs to be checked?

16th February 2010, 02:46 AM	#7
clayton diyAudio Member Join Date: Apr 2004 Location: LA.	Rockford is closed today due to presidents day. Will contact them tomorrow and get schematics. The amp powers up fine, it just does not produce any sound. Should I still cut the legs, or were you thinking that it was not powering up.

16th February 2010, 04:15 AM	#9
clayton diyAudio Member Join Date: Apr 2004 Location: LA.	DO they need to be out of circuit to do the test?

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