checked the voltage between pin 1 and pin 4 of the STR30130 -> 131V
checked for voltage on capacitor C536 (10uF / 250) -> 186V
Checking the voltage at the vertical output IC421 -> ok
I used a DVD player (player) in the audio and video input -> no picture with white screen.

Note: the flyback screen potentiometer setting is at minimum.
Image obtained according to the attached image

Although the voltage on the capacitor C536 of 10uF / 250v is 186V when the tube is not connected I am getting over the transistors RGB voltages of 35v on a transistor and 22v on the other transistors of RGB output (with the tube connected on the kinescope board)

Check the voltage of the accelerating electrode (screen) CRT.

Connect the kinescope board and measure all voltages and write.

I did the same test without the kinescope plate being connected to the tube and the voltages remain the same, ie with the kinescope plate placed or not the voltages remain the same.

I wanted to see if the problem could not be the potentiometer of the screen that is inside the flyback can not be defective?

If when adjusting the accelerating, the brightness does not change, it can.

I noticed that either the TV board connected or not in the tube the collector voltages on the transistors Q304, Q305 and Q306 (2SC3271) remain at the same voltage around 22v and 35V.

Now if I remove the K connector these voltages rise to around 200v. This connector is the connector that excites the bases of the RGB output transistors (2SC3271)

The problem is voltage SCREEN, or voltage HB_196V, or video processor, or signal ABL, or voltage 12V (connector K), or signal R-Y, B-Y, G-Y, Y (connector K), or
kinescope.