Stage 160 pre amp into FM 212 power amp question

[noviceamptech]

Hi guys. I'm new here and had a question. My bud has an FM212 that has lost its volume all of a sudden. The volume went away and it's kind of fuzzy, like a drive channel sounds when in use. He was saying that he was not sure if it was his pre amp or power amp and asked if I would plug my cord from my pre amp into his power amp socket. He did put his cord from his pre amp plug into the power amp. No change. He also plugged his guitar directly into the power amp and had fairly clear sound but not a lot of volume. So, he then plugged into my Stage 160 amps power port. The sound and volume was the same. Not a lot of volume but clear sound. Mine works find mind you. So I told him that his pre amp must be the problem. That's when he suggested plugging his pre amp into my power amp and viseversa. I guess my question is. Is this safe? I want to help him but am not wanting to take a chance of damaging either amp. To be honest, he does know a lot about amp repairs, at least way more than I do as a novice, and I don't know where he tends to go from there. He says that this would easily eliminate half of the amp for troubleshooting. Sould I let him do this or pass on it? Thankguys.

[Twist]

I think it will be fine. Just as a precaution make sure both amps are plugged into the same outlet and both AC cords have the ground prongs.

[Enzo]

That is exactly what I would do in my shop.

[noviceamptech]

Thanks so much guys. I guess he really did know what he was talking about. I am much more comfortable now that you agreed with him.