Arcade Monitor Color Problems

[kevin]

I'm running a JAMMA cab at the moment and am having a few problems with the video..

I first noticed problems when I installed a new board, which was also the first time I had it on for more than 5 minutes. Occasionally the entire screen would take on a blue or green tint for a second or two, then return to normal. I didn't have time to track down what it was back then, so I left it as is and hadn't turned it on much until recently.

The other day I turned it on to play a few games, and the color problem was still present. However, after about 30 minutes the whole screen took on a flickering yellow/green tint which has yet to go away. I took a few pictures which came out a little blurry, but you can see what's happened. It's hard to see the tint, but the yellow diagonal lines should not be there.

pic 1
pic 2

I found WG 19K 7611 on the chasis, and the tube says Phillips KO5, if that helps.

I don't know enough about monitors to know what might cause this, so any help would be appreciated.

-Kevin

[Ken Layton]

The picture tube has low emission and it has an intermittent short internally. These problems can be cured by connecting the tube to a restorer/analyzer (a.k.a. rejuvenator) unit. Tv repair shops can do it for around $50 to $75.

[kevin]

Ouch.. That's exactly what I didn't want to hear. I don't suppose theres any other possible cause? Dirty contacts, loose connections, bad power supply, bad caps, faulty game board? If not, I guess I'll start calling around town.

Thanks.

-Kevin

[menace]

On my q-bert I had the blue drop out intermittently--turned out to be a bad connection on the neck board--bloody thing was cracked--repaired and good as ever.  Check for cold solder joints, loose connections and bad pots--also, have you ever done a cap kit--always good to eliminate that from the to-do list.

As with the yellow lines, the only time i see lines like that is when the brightness control on the flyback has been cranked up too far--its hard to tell from your pic but it didn't look like your screen was that bright--so its hard to say.

[Ken Layton]

Here's a way of fixing it also. Visit this link:

http://slot-tech-ftp.serveftp.com:8080/monitors/hkshorts/hkshort.htm

[kevin]

Thanks for the link.. Even if the repair is a little beyond my skills, I atleast understand the cause/fix.

I don't believe the problem is as simple as a loose line on one of the colors, as all the colors are clearly visible at the test screen, and never cut out. The picture looked fine before the flickering, so I don't think it's in desperate need of a cap kit, though if I end up pulling it out of the cab I may as well do it.

I do have a few questions about the article though.. If there is a heater-cathode short, then that gun will fire constantly? The color I'm seeing, mostly greenish/yellow is far from the brightest green, and it is definitely not constantly present. I'm assuming this means that the heater is not in continual contact with the cathode, but touches it while vibrating? This is why I see the color flickering over the screen, with varying intensity over time? Also, I sometimes notice red as well as green, which would imply a similar problem with the red gun as well? Before the constant flickering began, sometimes the tint was blue, which could mean all 3 guns have problems?

If you believe you might have a heater-to-cathode short, try unsoldering and removing the associated video output transistor from the neck board of the monitor. Fire up the monitor with the transistor removed. If you still have a brightly colored screen with vertical retrace lines, there's a good chance the CRT has a heater-to-cathode short.

I don't see any transistors on the neckboard which I could remove. I'm guessing that just dissconnecting the video inputs from the harness isn't sufficient? I'm not at the confidence level to remove the tube and check resistances on each of the pins, so this is about all I can do.

Finally, could this be the result of rotating the monitor? I only had the machine on for about 10 minutes before I rotated the monitor, and didn't notice any problems back then.

Thanks again, the help is really appreciated.

-Kevin