Yet Another M-80 Repair Thread

[zaibatsu]

Most Yamaha amps use the chassis as the common ground, so they aren't separated as you say. If you check resistance with your meter between the RCA jack negative and the chassis ground terminal you'll notice only a 0.2-0.3Ω impedance, same with the speaker negative terminals.

It's believe it's best practice to not connect this to mains ground as that ground is a "dump" for noise from household switching supplies etc.
There shouldn't be any need to mains ground this amp as it's double insulated.

If the chassis were floating, you could earth it. But very few are with home audio gear. Connect the chassis to earth ground through the cord, and you'll nearly certainly end up with ground loop hum. Not dangerous, just noisy, and rather counterproductive to the hobby.

 

[rottalpha]

I want to see what happens when you connect a scope to that chasys now...to test sometin' ...Have the camera ready!

 

[pustelniakr]

Plug your scope into an isolation transformer, as I do. All will be well.

Enjoy,
Rich P

 

[amr2]

If the oscilloscope has plastic case, you can "float" it so that the local ground is not at true ground

 

[amr2]

I was just kidding, it's better to use an isolation transformer on the scope or on the equipment.

IMHO I wouldn't connect the chasis of the M80 to main ground.