Sound now works properly. I had to clean the speaker contacts.
About the monitor:
It is in very good shape.
Plugging it to the cab I had the spot killer on and no lights on the neck.
I cleaned all connectors but it was not sufficient. Then I realized that moving the cables I had some reactions and I checked the connectors solders and the red one on the main board connecting it to the HV unit has at least 5 pins interrupted. So 10 minutes with a solder and I remade the board like new.
Assembling the monitor inside the cabinet and cleaning the yellow layer and the black cardboard I can say most of the job has been done…
Most of the job has been done. Now the back panel is missing. Actually I don’t remember if I have it somewhere in my garage or I have to remake it. We will talk about this next week.