Question Technics SA GX100L no sound

[Rigsy]

We haven’t used our Technics stacking stereo system for a while, we plugged it in today and can’t get any sound out of the speakers with the radio or cd function. The CD works when attached to a different amp. All of the parts of the stacking system seem to be working - all have a power light visible. All cables / wires seem to be inserted properly. Does anyone have any ideas as to how we can test the amp or any solutions please?