Control 24 speaker noise problem

[dvodesilva]

Hi, I've just acquired a Control 24 from a friend and have a few issues i was hoping you guys can help me with.
First of all this is a control 24, not a c24. The first thing is my main speaker output seems to make a loud pop noise when i shut down the board, also it seems at times that my speakers are dropping to a lower volume randomly and the only way to remedy this is to turn the main speaker knob all the way up, then it seems that the speaker are at the volume they should be, then i can turn it down and with the speakers giving an accurate volume. i've seen an old post of cleaning the boards speaker contacts, but couldn't find any directions on how to do this.
the second issue is that my talk back switch intermittently goes out. The light doesn't work and i have to keep pushing the button to make it work, but somedays it would work just fine.
The last thing is some of my faders wouldn't go all the way down when shutting down the board.
sorry for all the questions and lengthy post, but i already had two tweeters blow out on my ex66 monitors because of this and im worried it could cause more potential problems.
i'm pretty technical and would prefer to try to fix it myself before i head to a repair shop.

Thank you all so much in advance for any help and suggestions that you might have.