First off, disconnect the speakers!
Break out your meter & see if you can measure any dc voltage on the speaker jack.
If so, the amplifier needs work.
I always test the power supply.
Both + & - rails should be the same.
You can access them right on the case of the power transistors.
Look for Vac ripple on the power rails & the opamp supplies.
The power rails can have a small amount of ripple.
The opamp supplies should see none. (pin 4 & pin 8)