Thanks a lot chromesphere, ashcat_lt, and R.G. My Rat now works!
When I got home yesterday, I did first watch the video chromsphere posted (http://www.youtube.com/watch?v=JnD4-_Fhd90
) and followed every step of the way. I get into the part where I need to examine the PCB with a lamp and with a Magnifying glass. And Booom!!! I've found there was a hairline cooper connecting between resistors 10K, 1M and the OUT. Amazingly, I can't see it without a Magnifying glass.
Root-cause of the problem:
1. Poorly etch PCB caused by carelessness or just a human error.
1. Follow the steps shown at http://www.youtube.com/watch?v=JnD4-_Fhd90
before doing other debugging tips.
2. What is a feedback loop
3. What are inverting and non-inverting input and what does it do
The problem with taking a wire to the output is that the output is pulled to ground by resistors or the amp input. If the resistors are big, the opamp output pulls the amp input too high, and if they're low enough to pull the opamp output down, the opamp can't work right. There needs to be a capacitor in series with the output pin of the place you're testing.
It would be very worthwhile for you to make a temporary audio probe from your output jack and a spare capacitor for testing. You can unsolder and resolder when it's working right. See http://geofex.com/FX_images/audioprb.gif
Thanks for the link. Very well illustrated. I will definitely create one those.