[sci.electronics] Space Wars Video

irwin@m.cs.uiuc.edu (11/16/89)

/* Written  3:17 pm  Nov 14, 1989 by usenet@cps3xx.UUCP in m.cs.uiuc.edu:sci.electronics */

>A "friend of mine" (no really!) has a Space Wars video game which is
>slightly defective, and has enlisted my help to bring it back up to
>mint (1977!) condition.  The problems lie in the video section.
>Specifically, the VectorBeam (tm) vector display.  The display is very
>dim and can only be viewed in a totally dark environ.  The yoke amp is 
>fine, as everything is in the right place...just very dim.

....Some text deleted...

>mail at

>beyer@frith.msu.edu

>or lemense@msupa.msu.edu

>I'm lost in a sea of High Voltage!

>Tom LeMense
/* End of text from m.cs.uiuc.edu:sci.electronics */

Tom, I serviced TV for one heck of a lot of years, and my intuition
tells me that your problem is not high voltage, but rather a low
emission CRT. The filament in a CRT heats the cathode, which is coated
with a white powdered substance to increase emission. The surface of
the substance becomes oxidized and emission drops. Heating the filament
to an above normal temperature increases emission and helps to burn
off the oxidation. This was the pricipal of the picture tube rejuvenator
which was a picture tube tester carried around by the service man. He
could "shoot the tube" and nurse it back to health.

This used to be a problem with old TV sets and there used to be
"Pix tube brightners" on the market that would help the situation.
What they were was a step-up transformer with a plug and socket
attached, where all signals to the CRT were straight through, except
the filament. The filement voltage went to a transformer, which had
a ratio of a little more than 1:1, so a 6.3 volt filament voltage
was stepped up to maybe 7 volts. Some of the more elaborate ones
even had adjustable taps with a lead and several holes that it could
be plugged into, to change the ratio.

To use the brightner, one simply unplugged the socket from the CRT
neck, and connected that to the plug on the brightner. The socket
from the brightner was then connected to the CRT neck.

To prove if this is your problem, you could disconnect the filament
leads from their source and power the filament with an external
adjustable power supply. DC will work, even if the tube is powered
with AC in the device. If you slowly increase the voltage to the
filament, watching it glow in the neck of the CRT, and monitor the
amount you apply, you can see if a slight increase helps. Measure
what the normal voltage is on the filament, under normal operation,
so you have a feel of what you should apply. Increase this amount
by 10 to 15 percent and see if you get improvement. This will tell
you if it is the CRT or not, and you might be able to burn off the
oxidation and improve results. 30 seconds at 8 volts, and then drop
back to 6.3 and see if it holds is the way to do it. Note, that is
assuming that 6.3 IS the voltage. Some CRTs have other voltage levels
on the filament, like 2.5 volts, so proceed with caution.

Hope this helps.

Al Irwin
Univ of Illinois
Dept of Comp Sci
irwin@m.cs.uiuc.edu