That's an Italian made Hantarex Monochrome Monitor Chassis, and a common cause of the screen going uncontrollably bright is dry–joints on the little panel that plugs on the back of the CRT neck – take GREAT CARE if you remove it as the CRT pins are very easily bent over and you can also accidentally break the glass pip off in the middle of the base!
If you look at the small CRT base you will see a circle of seven pins with a gap between two of them – counting clockwise from the gap, the base connections are :–
1 :– Grid (G1) – typically 0 to about – 20 V ;
2 :- Cathode (K) – typically +50 V to +80 V ;
3 :– Heater (H) – 0 V ;
4 :– Heater (H) – +11 V ;
These little CRTs use a heater rated at 11 V 60 mA !
5 :– Grid (G1) – Connected internally to pin 1 of the CRT ;
6 :– First Anode (G2) – typically + 90 V ;
7 :– Focus Anode (G4) – typically 0 V to + 90 V, varied by the "focus" preset if one is fitted !
It is normal for the preset control to have only a very slight effect on the sharpness of the text displayed, and with an old tube, you probably won't see any obvious effect of adjusting it !
I've attached the service manual for it for you !
Check choke B200 and R200 on the little CRT neck board for dry–joints, also R64 and R66 on the main monitor board for open–circuits, and resolder all the pins of the flyback transformer – the 15 kHz h.f. pulse voltages and the heat generated cause the solder to decompose round all the transformer pins !
You might have to replace the video transistor TR202 on the little CRT board if it has gone short–circuit !
If you're really, really unlucky, the CRT itself might be at fault due to a heater–cathode short, but in all my years of servicing CRT monitors, I only came across this fault once – it's much much less prevalent than it was in the old days of black–and–white TV only !
Chris Williams