Google it, otherwise I am no help.
If you only just want to know its output, measure the power rails for the power amp supply. The peak output will be a little less than those voltages (the positive and negative should be about the same, so measure one of them). Your output to the speaker will have a similar peak voltage. RMS is .707 times peak, and with 8 ohms and the RMS voltage, you can approximate the power output.