Mcintosh ma6600 strange signs on display

Glad I could help.  Enjoy your Mc - it's a nice rig.

Wow, yes! It's done! The problem is gone, thank you very much mr.Effischer! I made Master reset and everything became correct.
Thank you!

First, unplug the unit from the wall socket for a minute or two.  Then, plug it back in, turn it on and see if the problem goes away.  If so, good.  If not, go through all your settings, note them down and then do a factory reset.

After you reinstall your settings, check it again.  You should find that everything is back to normal.  If you're still having a problem, you'll have to go through the isolation drill with all the upstream components and identifying anything that might have changed or happened between the time it last worked properly and when you noticed the error.

The preamp section can encounter errors in low voltage or momentary outage conditions.  Usually, just unplugging the unit will take care of it, but sometimes a reset is needed.

Good luck & happy listening!