You have to narrow down what is not working - readout focus, readout character size, banding on the waveform display, crappy blanking etc.
The sine wave looks not so great, you can see two intermodulations causing banding and some sloppy blanking, presumably during the time slice the readout is displayed.
I would first ensure all power supply rails are correct and their capacitors are not bad.
The readout intensity and focus look way off. I can't tell where you have readout intensity or stored waveform intensity set on the front panel.
If the power supply is OK, you could try the focus switch/amplifier trimpots sheet 13, Focus gain R63, Focus output level R70.
Again, nothing should be that far off unless a component has failed, so trying to fix it by adjusting a trimpot has limits.
W140 Tektronix 7854 wiki