[Chris K]

Originally Posted by Zenith26kc20

The brightness control goes from 135 volts fed by a 12 K resistor going thru the control to ground. If it does pull a short to ground, the 12 K would overheat and possibly pull the 135 low. This 135 volt source feeds the I F screen grids also. If the control is grounding, check for tin whiskers on the control. Changing the 135 source in relationship to ground will, thru the screen voltages changing, affect the amplification factor of the I F and cause quite a change in the I F.
I would monitor the brightness control to ground as I rotate it for a drastic voltage change.

Check the 135V correct?