Monochrome Computer CRT Brightness

[zeno]

MOST of the times on SS sets the cathode is where the video comes in.
Voltages will stay about the same otherwise.
There is a video output transistor ( 3 on color CRT's). If the brightness
is increased the voltage on the C voltage goes down. If you turn the brite
all the way up the C voltage goes up to the B+ value. No raster results.
SO if you get a good pix after the sub brite adj either that pot has
a bad spot or something is "off".

For the SM if the set has an FCC ID number or "type acceptance"
number look it up at FCC.GOV That will list the MFG of the
actual builder & its model number. Take it from there.

73 Zeno
LFOD !

[TinCanAlley]

Originally Posted by zeno

MOST of the times on SS sets the cathode is where the video comes in.
Voltages will stay about the same otherwise.
There is a video output transistor ( 3 on color CRT's). If the brightness
is increased the voltage on the C voltage goes down. If you turn the brite
all the way up the C voltage goes up to the B+ value. No raster results.
SO if you get a good pix after the sub brite adj either that pot has
a bad spot or something is "off".

For the SM if the set has an FCC ID number or "type acceptance"
number look it up at FCC.GOV That will list the MFG of the
actual builder & its model number. Take it from there.

73 Zeno
LFOD !

This monitor is from '84. I noticed that turning the front brightness and internal sub bright affects the voltage of the cathode (I believe that is the negative value that controls the G2's emissions). Anyway, with all the brightness controls down, it put out roughly -130V. As they increase, the voltage drops to -2V or so and the screen illuminates. Never able to get a full raster, but bright enough to use and sharp focus.

So I am wondering that if the G2 is 628V at the socket, and G1 is -2V in order to produce an image, then the CRT is basically toast? If not, what else could account for the need to crank the G1 (brightness and sub bright) in order to get an image? I can easily use this monitor as is, but know there is something wrong and that drives me crazy.

I looked up the FCC stuff and it notes it as being a CRT type device, but goes no further. Doesn't provide enough to find a service manual or other usable specs.