About Sony KV-1300 thyristors...
 

I found a Sony KV-1300, but it doesn't work (need to push the rear safety switch every time). The problem seems to be in the two classical thyristors, but this is the first time that I try to fix a set like this and you wonder if I have to check some component that may have caused the damage of the thyristors (some capacitor, defective welds, etc.).

Thank you in advance

I think that model uses transistors, instead of a single thyristor. You have to check them for shorts. They usually fail from lack of horizontal drive. The loss of drive is usually caused by loose connections on the drive board.

You have right, it uses two transistor in the horizontal section and other two in the power supply, thanks for the advice!