Car Amplifier Repair Help

[tigerstyle]

I have this Kenwood KAC-521 amplifier here, it's only small but my car and speakers are only small so it's ok
I installed it and it worked for about 2 weeks, but now only the left channel is working, the right channel is very quiet, seemingly quieter than if it was running straight from the cars headunit.

It's not the cars speaker wires as  I swapped left to right and vice-versa, and I've swapped the RCA inputs also, it's always the right channel that is dead.

I've looked over the board and  I can't see anything obvious, but my skills go as far as checking voltage and looking for blown caps... 

Wondering if any people here have car amp related skills and can point out obvious stuff  I can check?

Images in links here:

[AmmoJammo]

That amplifier will only do the same output power as an aftermarket (and most standard/factory) headunit anyway.

[tigerstyle]

That amplifier will only do the same output power as an aftermarket (and most standard/factory) headunit anyway.

It's more powerful than my headunit, and when it was connected the sound was noticeably clearer and louder, so is worth having.
I know the '50x4 Watt' on most headunits is a made up figure too, mine is a cheap headunit so is probably only half that anyway.

[David_AVD]

So the right output of the amplifier is dead (very low) no matter how you swap the input and speaker wiring around?

I'd look for cracked solder joints first.  Otherwise it could be that the right channel amplifier chip has been damaged by an intermittent short in the speaker wiring.

[AlfBaz]

Being 2 channel you could try following the signal path with your multimeter, comparing channel to channel as you go. Somewhere along the line you'll get a difference between the 2 channels.

If you don't have a scope to look at signals and the input is from a head unit who's signal can drive a speaker anyway, you could attempt to use a speaker to probe for signals. If the amp's inputs and outputs are referenced to ground (check for continuity between the RCA shields to ground) attach one speaker lead to ground the other (with a large cap to block any DC bias voltages and a 5W 50 to 100 ohm resistor in series to reduce circuit load) and start probing

[KK]

Use an esr meter and check the capacitors. They could have failed without obvious visual signs.

Check the FET's that are mounted on the heatsinks. Google for the FET test procedure with a multimeter.

Those are your two most likely culprits aside from obvious wire or trace damage.

[tigerstyle]

Thanks for the pointers, I'll go google some guides

[Rasz]

one of TA7251 is probably dead
http://www.chinaeds.com/zl/Laoli%5Cjcdl%5CTA%5CTA7251BP.pdf

diagram
http://www.manual-buddy.com/manuals/html/BE/13/BE1319FC06BEC30C114686758F9DAAA4AAFFAAD8/BE1319FC06BEC30C114686758F9DAAA4AAFFAAD8005.png

unplug the unit and compare resistance between legs between two chips for a quick dumb test

[Refrigerator]

Is there a noticeable drop in audio quality between the two channels ?