Blown amp (reversed polarity)

[tjmehta]

Hey guys,
I have a 'boss audio rip 896' that i hooked up wrong; I hooked up the power to the gnd and the gnd to the power. I saw a long zap...I hooked it up correctly and the protection light keeps coming on.

I opened up the amp and tested the MOSFETs BJTs and all other transistors on the sides. All of them are okay..none are melted at all ..and all test correctly with the diode check on my digital meter.

I next tested the reverse polarity protect diodes..those were fine.

I tested the input filtering caps and those seem to be fine also.

I am totally lost now on what to check. I want to believe its the temp sensor (thermister / thermoresistor)..or maybe even the logic chip (or op-amp or w.e that chip is, 's494p').

What fully confuses me is why the reverse polarity path didnt protect the rest of the circuit. The path goes through the diodes and directly to the fuses... but neither blew.

PLEASE HELP!
tj

[poobah]

got a schem?

[anatech]

Hi tjmehta,
If everything but the power was hooked up and you hooked up positive first, you burned the ground traces or resistor between the signal ground and power ground. It is possible to cook a heat unit that way, or crossover (or all of it really).

Check with an ohmmeter first. I'm hoping it was just the resistor that is commonly used.

-Chris

[tjmehta]

I just took a look at that. it doesnt look like there is a resistor there..there is actually a capacitor there.


am i looking at the right thing (attached pictures)


any other guesses?

thanks

[tjmehta]

another pic

[anatech]

Hi tjmehta,
Have a look near the input of the amp, or between the power and amp sections. You need a DC path and that will not be a capacitor. Some resistors can burn out and look perfectly fine from the top.

-Chris

[tjmehta]

i tried to attach pics to my previous posts...but i dont think it worked

so i posted them on my website ::

http://www.prism.gatech.edu/~gtg158w/gndpic.jpg
http://www.prism.gatech.edu/~gtg158w/gndpic1.jpg
(not the cap being tested)

If u can see the numbers...it says C51..C=cap

is that the right point im looking at though..or where should i look?

thanks

[tjmehta]

im looking around the inputs for a burnt resistor...

i tested the resistance btw the pwr ground and the rca inputs' ground and both came up with a resistance. so nothing should be burnt out.

[anatech]

Hi tjmehta,

i tested the resistance btw the pwr ground and the rca inputs' ground and both came up with a resistance.

What value did you come up with?

A blown resistor would have been the best outcome.

Have a good look at the bottom of the board. Take your time and use your glasses, or if you aren't like me, a magnifying glass.

-Chris

[tjmehta]

it has two L/R pairs (4 channel amp)

each of the RCA-GNDs individually to the PWR-GND => ~4.67ohms