[HECnet] VT420 with a "worn out" display

[Dave McGuire]

On 10/04/2013 12:31 PM, Cory Smelosky wrote:
Saku Setala donated a VT420 a while back but the screen is almost
unreadable, unless you turn off all ambient light.

Is there any way to fix this?

Increase the current to the electron gun.

  The issue here is weak cathode emission.   This happens as a CRT ages.
Crap builds up on the oxide coating on the outside of the cathode
impedes its ability to emit electrons.   This is generally known as
"cathode poisoning".

  There are ways to "rejuvenate" the cathode by applying high-voltage
pulses to it and nearby electrodes like the control grid.   There are
devices built to do this.   If you find an elderly TV repair person,
he/she will likely have one.

                          -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA