Amp has very low output.Rail and REG voltages present.If i pull the RCA jack out and rest the tip/signal to the input shield of the amp it will play and sound like normal with expected output .Any idea why it is behaving so?
Check DC voltages on pre-amp header pins and post.
I don't recall an amp behaving as you describe with signal feeding through the ground loop. Check for broken traces or leads on RCA 's.Also check between signal and power grounds. 2006 models should read open or high ohms. 2008 and later models should be a dead short.
It looks like the power and signal grounds are open. A common problem with this amp is an open resistor/jumper R70-0 ohm 1/2watt, you may have a blown trace on the underside of board as well. But I would check from top side before you remove amp from chassis, because the resistor can be replaced from the top.
With the amp oriented so that power terminals are on your right, the resistor will be just above input filter inductor and behind the 820uf/160v filter caps. You can check and replace this resistor from the top. Make sure that you have a dead short from the Power Ground and Neg Spkr Ground terminals.