Arcade game monitor problem

[Ken G.]

I have an old asteroids full size vintage video game .
I has a black & white monitor .

When it first comes on its fine . Within 10 minutes the whole image gets
bigger , things disappear off the edges . The center of the screen gets
a bit darker .
I suspected the hi voltage diode off the flyback and adjusting the hi
voltage pot but replacing that did not help .

I dont have any model #s the monitor has one medum circuit board and
one small board with the flyback in a metal box .

Thanks

 

[Ken Layton]

rec.games.video.arcade.collecting is the correct newsgroup.

 

[Franc Zabkar]

I have an old asteroids full size vintage video game .
I has a black & white monitor .

When it first comes on its fine . Within 10 minutes the whole image gets
bigger , things disappear off the edges . The center of the screen gets
a bit darker .
I suspected the hi voltage diode off the flyback and adjusting the hi
voltage pot but replacing that did not help .

I dont have any model #s the monitor has one medum circuit board and
one small board with the flyback in a metal box .

Thanks

The "blooming" does sound to me like a low EHT problem. I'd check the
B+ going to the FBT, and the base drive to the LOP transistor. Make
sure the duty cycle doesn't change. I've seen this happen in an old
IBM monitor as a ceramic capacitor in the horizontal oscillator warmed
up. However, in my case the EHT gradually increased until the HV
protection shut down the monitor.

- Franc Zabkar

 

[Ken G.]

Thanks Franc .. I dont know which conection is B+ on this . It seems to
be a Wells Gardner monitor according to a website provided i an arcade
newsgroup .

 

[Franc Zabkar]

Thanks Franc .. I dont know which conection is B+ on this . It seems to
be a Wells Gardner monitor according to a website provided i an arcade
newsgroup .

I would think that one end of the primary winding would be connected
to the collector of the switching transistor, the other to the B+.

If the FBT has any part numbers, try locating a substitute here:

http://www.hrdiemen.es/products/index.php?command=viewSection&id=4&language=eng-GB

The HR substitute will have a wiring diagram with voltages.

I notice that the Wells Gardner Quadrascan colour monitor at the Atari
link provided by Dean uses a HV regulator circuit that senses a 180V
pulse from a tap on the primary winding and uses this feedback to vary
the B+ to the FBT, and thereby control the EHT.

- Franc Zabkar

 

[Yukio YANO]

I have an old asteroids full size vintage video game .
I has a black & white monitor .

When it first comes on its fine . Within 10 minutes the whole image gets
bigger , things disappear off the edges . The center of the screen gets
a bit darker .
I suspected the hi voltage diode off the flyback and adjusting the hi
voltage pot but replacing that did not help .

I dont have any model #s the monitor has one medum circuit board and
one small board with the flyback in a metal box .

Thanks

Sounds to me, more like the Filament Voltage is dropping, cold solder
joint in filament circuit ?

This describes what happens to the image when I reduce the filament
Voltage on my Transmission Electron Microscope !

Yukio YANO