Is this diode for UHF only or what is its purpose? I know it blocks voltage to flow only one direction, just trying to get in my head how it works in a chassis.I found this one open, set screw had been moved and some one pushed it back into ceramic to the point it was not working and the inside diode cold not be moved back out so set screw could lock it in place.

Its role in life is a mixer diode. Mixes UHF osc with the incoming
UHF signal to get the TV's IF frequency.
When you turn to UHF the following happens.
The UHF tuner B+ gets turned on.
The VHF RF amp & mixer tubes are turned into 2
more stages of IF amps & the VHF osc is turned off.

73 Zeno:smoke:

Zeno thanks for clarifying that, I had raster only no pic and garbled sound thought I found problem since its only UHF not the problem.