P3A won't work

[Austin]

I just finished wiring up my P3A. I tested with the 22 ohm safety resistors in place of the fuses. The LED lights up and everything appears fine. The voltage at the output is less than 1V. However the resistors get VERY hot. The voltage drop accross the resistors is almost 22V! It is the same for every channel. They all read almost exactly the same drop accross the resistors. This led me to believe that I had put in a wrong component. I looked over everything very carefully, twice and found that the NPN and PNP's were switched at the outputs. I changed this and tested again. The voltage drop accross the safety resistors is still the same. The voltages provided by the power supply seem to be fine, so I'm guessing the problem is in the amp. Does anyone have any recommendations? Thanks in advance,

Austin

 

[bigparsnip]

Are you sure the output transistors are still ok? As if they are damaged they could be shorting out and dropping tthe supply voltage from one (or both) rails accross the output resistors.

 

[HDTVman]

I think I'd check all of the transistors. If the outputs failed shorted, they could take out the drivers etc. Transistors don't like to have the voltage reversed.

Later BZ

 

[tiroth]

Check the drivers first. (BD139/BD140)

 

[darkm4n]

For shure you damage the output transistors ... they are shorted ..

 

[sss]

For shure you damage the output transistors ... they are shorted ..

if u used the 22ohm resistors correctly then nothing should happen to the power transistors