Make sure your voltmeter is working. Try measuring a 9 volt battery.
Be sure you have a good ground for the negative lead of the voltmeter. Either speaker (-) output points would be a good ground. Somethines trying to use the chassis can be problematic.
Turn the unit on, with the volume turned all the way down. It is not necessary to have the speakers connected. *Carefully* probe each pin of the amplifier device being careful not to short between adjacent points.