Tektronix 7514 scope vertical noise on display

[Creede]

I have a 7514 storage scope that a friend asked me to attempt to repair.
It has vertical noise on most selected voltages on both vertical input units.I have looked at the voltage test points and most have 200 to 300 mv of almost a sine wave of noise.
I suspect the power supply (inverter board), but don't know how to remove it from the case. I removed the 4 screws on the back but nothing moves. Don't want to do more damage.
Any thoughts or help will be appreciated.
Creede

 

[PETERDECO]

Before doing anything, clean all switches and controls with contact cleaner. Give the PCB mounted trimmer pots a blast also.

 

[Creede]

Before doing anything, clean all switches and controls with contact cleaner. Give the PCB mounted trimmer pots a blast also.

Thanks for the reply. I did already clean the switched with contact cleaner but not the pots. I will do that right away. The pots are a little tricky to do since I don't want to change the settings by moving the shaft of pots on the PCB.
Thanks again. Creede

 

[Creede]

Everything sprayed with contact cleaner, no help.
The signal on the voltage test points is 25 Khz with some points show the second harmonic, 50 Khz. Pretty sure it's coming from the inverter board but, as I posted before, I don't know how to get the power supply out of the case to check the board. I have removed the 4 screws on the back, but it does not move.
Help me out please.
Creede