I have built 2 of these amplifiers(Right and Left) and R works and L doesn't.
For the faulty one, I have built it twice so the next time will make 3. I would like some guidance to try and figure out what I am doing wrong.
I built it (I thought) according to the schematic but both times when I put it in the chassis and power it up, I get a .22 shot sound, smoke, and in one instance, a fire. Both times it seemed to be on resistor 4, 20K.
The resistor looks like it has 2 chips taken out of it but it still tests 20K.
Resistor 4 is soldered to the back side of the PCB. The PCB is mounted on 1/2 inch plastic risers.
I completely desoldered board L1 and tested all the parts and they all tested ok, including resistor 4. The only thing that I couldn't or didn't know how to test was the LM3886 IC. So, I bought some new ones and put it in.
So, L2 was with a new LM3886 and the salvaged parts from board L1. Before I put it into the chassis, I hooked it up to my bench power supply and ran it up to +30DC, and -30DC and it seemed to work ok.
I put L2 into the chassis along with the R1. applied power and L2 .22 shot sound, and smoked again.
I took L2 out and have been trying to test it outside of the chassis and it seems to work ok.
However when I put it back into the chassis, at least I dont get any shots nor smoke but I think that it is not performing correctly.
I took some voltage readings and tried to compare both boards.
Something strange that I noticed was this. V- was measuring -5 Vdc with no connection to the power supply. With it normally connected, it should read -26Vdc
I dont know where to start. I was going to build another amplifier board using the scavenged parts from L2 but I am reluctant to plug it into the chassis and apply power to it.
I think that I will build it and swap it with the working amplifier, R1. If R1 shorts then that will tell me something,,,,, that I will have to think about.
Could it be the wiring into the chassis or the power supply ?
I dunno