I can't see the entrance guard image at home. They are all white. What happened?

This may be a fault in the output circuit of the entrance guard display, for example:

1, the field amplitude potentiometer is broken or out of balance.

2. The field scanning output integrated block is bad.

3. The amplification value of the field output tube changes, and the output capacitance is poor.

4. The negative feedback element used to improve the nonlinearity in the field scanning circuit deteriorates, resulting in the change of feedback quantity.

5. If the magnetic field linear compensation capacitor or output coupling capacitor is damaged, replace it after troubleshooting the faulty component.