Rockford Fosgate T8002 Amp diagnosing help

[joocyj]

Just looking for someone to help walk me through testing components on the unit. unit powers up and produces very quite and limited signal.

 

[Perry Babin]

While listening to the amp (speakers and signal source connected), operate all externally accessible pots and switches through their entire range to see if audio ever plays through normally.

 

[joocyj]

Already done. All seem to work and have an effect but nothing close to normal output. tried both speaker outs with same results and different load speakers on as well.

 

[joocyj]

Picture of the amp for visual reference

 

[joocyj]

Just for my ease of mind, do you know if it would make a difference if my input signal just came from my cellphone directly to the amp via a headphone jack-rca cable? i'm not sure if i'd need a powered unit of some kind to get correct results while bench testing.

 

[Achim1409]

Cellphone has not enough output. You should use a headunit.

 

[joocyj]

Thought that might be the case. Just finished hooking up an audio deck and same results. Both output channels send audible signals, but all volumes turned up is still hardly audible.

 

[joocyj]

I have tested voltage on what I'm assuming are fets around the outside edge of the board. Starting on the right side by the power and ground inputs, i get constant readings from chip to chip up until what would be the 9th-12th chips where the is a visible size change. Varies readings on the next 4 smaller chips, and then no voltage at all beyond that for all the chips beyond that point.

 

[Perry Babin]

http://www.bcae1.com/temp/100hz300seconds.zip

Drive the signal above into the amp. Measure the AC (not DC) voltage with the black probe on the RCA shield and the red probe on the center conductor of the RCA jack (behind the jack in the amp). Do this with the signal source set to full volume. What is the voltage?

As a side note... I didn't know what a cell phone output could produce so I measured mine. With the signal above, at full volume, it produced 0.6v RMS.

 

[joocyj]

Wasnt sure exactly what I'm probing when you say "center conductor". Included picture of RCA jack and components behind for reference.

 

[Perry Babin]

See attached. The highlighted piece of metal is where the RCA center conductor will make contact.

 

[joocyj]

it seems like its .5v ac straight from my phone, and from my deck it was .7v. Will double check that when I get home.

 

[joocyj]

So double checked just now. About the same through the phone, .4-.5v. Through the deck read out about 2.0v this time, both left and right rca ins and consistently.

 

[Perry Babin]

With that input signal and level, what's the AC voltage across the speaker terminals of each channel with the gain at the max position and the crossover set to full range?

 

[joocyj]

just to be clear, am i probing a positive and negative of each channel to get this reading?

 

[Perry Babin]

Yes

 

[joocyj]

Same results on both left and right input. 0.6v ac with no speaker hooked up. Shows .0 volts with a speaker hooked up.

 

[joocyj]

*outputs

 

[Perry Babin]

Was that on AC voltage?

 

[joocyj]

Yes. I have a better dmm at work than i do at home, i'll try to remember to grab it an check using it as well.