WG k4900 Missing Green (fixed)

[ncflagg]

I have a WG k4900 that seems to be missing green. I put a cap kit in it just now because it was dark but I think it was dark because green is gone. I can see some green bleed in the black background if I turn up the green dial on the neck (or if I turn up Screen). I saw a suggestion here http://www.2coinsperplay.com/Tech/Monitors/K4900%20HTML/Color.htm on checking some transistors but I didn't find anything out of the ordinary comparing the green trans with the adjacent ones. Could it be that the Jamma board isn't outputing green maybe?

Ideas?

[SirPeale]

Could be.  Switch the color input wires around and see if any new colors pop up.

Could be your tube.  Though it's usually red that goes first.   

How did you test the transistors on your neckboard?

[ncflagg]

I put the multimeter in resistance mode and diode mode and compared numbers to the ones next them. What's the correct way to test them?

[SirPeale]

Did you test them out of circuit?

You could swap transistors, say red for green, see if the problem travels.  If it does, you've found your problem.

[cw]

you did check for coldsolder and reflow and joints that needed... like the input pins...

[Kevin Mullins]

you did check for coldsolder and reflow and joints that needed... like the input pins...

Also around any larger resistors on the neckboard.

Since you have SOME green..... it could be a faulty potentiometer or a weak tube gun.

[ncflagg]

If by "testing them out of cicuit" you mean removed from the circuit board then no. Will the test not work unless they're pulled? I'm not sure what cold solder means but conductivity checked out from the input pins to another point down the line. I'll trace it further and see how far I can get. I didn't notice by sight anything that needed resoldered. Should I be looking for something or just reflow the big resistors? How would I check for a faulty potentiometer (I assume you can't do anything about a weak gun)

[ESDAVE]

hi an easy way to check if your crtube is at fault , disconnect neck board from crt  prop up securely then check cathode volts R/G/B if they are all the same crt is the fault if you find green volts only wrong then not CRT. if you require more info post again.kind regards dave UK.

[ncflagg]

I swapped the video connection from "missing green" un squadron to the nice double dragon monitor (both 4900s) and I see no green and it is a little dark. If I put the double dragon output to the un squadron I can see green and everything is still a little dark but very washed out.

It seems that there is a problem with the jamma un squadron outputing green AND the tube has lost its usefullness.... Unless anyone has further thoughts.

[Ken Layton]

Have you adjusted the "Black Level" and "Screen" controls?

[ncflagg]

There is a pot next to h hold that effects brightness but turned only 75% down the screen goes black. Turned up all the way all of the colors start bleeding. Screen also makes it brighter but not before the black background turns green.

[Kevin Mullins]

black background turns green.

A couple times now you have mentioned seeing green....... which means your pcb is outputting a green signal to some degree.
I would absolutely double check the green control pots on the monitor. There is usually TWO pots.
Turn the SCREEN control until you see the green background like you mentioned...... then adjust the green control pots and see if they make a difference at all. This should give you a quick idea if they are even trying to work.
You should actually ohm them to be certain that they have full range.

[ncflagg]

I tested the voltages of the R G B wires coming from the Un Squadron board and found that the Green had much lower numbers. I hooked up the Double Dragon to it and took off the smoked plexiglass. I immediately noticed heavy burn in under the sunlight. I closed the garage door and tuned it in best I could. Green is there and the screen is a little blurry. I may attempt a tube swap if I can find an old enough tv in the future.

Could there be a green pot on the un squad board?

[ncflagg]

I found a TV that looked right and swapped the tube. The screen is a little "smashed" vertically. Adjusting the VSIZE pot separates a small section of the top on the image from the rest. I used the original yoke and rings from the TV tube. I did a swap on a Sanyo 20 ezv a couple days ago and did not use the old yoke and it worked fine so that's what I tried here. Thoughts?

Edit: The new tube's yoke is low (10) impedance and the original's yoke is high (80). Can I add some resistors to the neckboard somehwhere? Do I have to swap the yokes?

[Kevin Mullins]

Edit: The new tube's yoke is low (10) impedance and the original's yoke is high (80). Can I add some resistors to the neckboard somehwhere? Do I have to swap the yokes?

Bad ....

Swap the yoke out as well.
If you run it too long like that it may damage the chassis.

Do you see a difference in color? (green especially)

[ncflagg]

Yes the colors all seem to be there. Green is back.

So if I swap the yoke do I keep the purity rings from the new tube? Will I have to readjust the rings?

[ncflagg]

I swapped the yoke out and used the purity rings from the new tube. The picture was upside down and inverted. I swapped both the vertical and horizontal yoke wires and then it was right side up but backwards. I finally found the right combination of swapping the horizontal wires only fixed both problems. (I don't claim to understand why)

I was still having problems with heavy static and dark picture intermittently. I found that the video connector coming from the Jamma harness had bad contact on the punch-down wires. This may have been my original probem (I.E. missing green). Every time I would try to fix/fiddle with it, it would do something different.

Anyway, the burn-in is gone and I learned something....

Thanks, everyone.