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
rec.games.video.arcade.collecting is the correct newsgroup.
On Wed, 22 Oct 2008 08:22:07 -0600, snipped-for-privacy@webtv.net (Ken G.) put finger to keyboard and composed:
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
-- Please remove one \'i\' from my address when replying by email.
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 .
This is an XY monitor, the scan is very different compared to a normal tv.
Try this Page
The fault sounds like b+ is going low, maybe a bad cap in power supply. I think from memory its 123v to HT Generator Board.
On Fri, 24 Oct 2008 08:33:20 -0600, snipped-for-privacy@webtv.net (Ken G.) put finger to keyboard and composed:
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:
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
-- Please remove one \'i\' from my address when replying by email.
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
Your _own_ TEM? Really! Do you have photos of it on a site somewhere?
Michael
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