1 - Put the amplifier on its rear handles on soft material...
2 - Unscrew TOP & BOTTOM panels.
3 - Disconnect the LED from motherboard (FLAT WHITE WIRE).
3 - Unscrew the FRONT Panel from aluminium rail (You'll see it easily).
4 - Move the jumper to BLUE.
5 - Put back together and test.
And... while I was there... I dust it off a little
Just like a brand new one!