WG K4900 Monitor Color Question

[DjDonnyD]

Hello,
I have a wells gardner k4900 monitor that has no blue in the picture. Other than missing the blue the picture looks real good. I had someone tell me that it needed a capkit, WRONG! I did the capkit and it is still the same! I idea what would fix this problem? Thanks Sooo Much! Donny

[Kevin Mullins]

Take a look at the neckboard on the tube for hot spots, cold solder joints, etc.
Meter the three transistors you will find on there. There will be one for each color, RED, GREEN and BLUE. Check the resistors going to each of the color circuits on the neckboard as well.

You could also swap the color input leads around to verify that that particular color problem is for certain a moniotr problem.
IE: Take the blue input line on the monitor and apply it to where the red one is now. If you get picture(red) then you know for sure that the game pcb's color output is working fine for the blue. Which also means that it is for certain a monitor issue. (take the red one out before doing this)

But more than likely the problem is on the neckboard.
(gonna take a shot in the dark here)

There are transistors and such to check on the main chassis as well near the video input.....but let's make that step two. Let us know what you find on the neckboard first.

Absolute worse case scenario is that the blue color gun has died in the tube itself.
(but lets not go there just yet)

[DjDonnyD]

Hey Kev,
Thanks for the reply,
I pulled the monitor out of the cabinet last nite and installed it in another cabinet. This cabinet has a different harness and game board. But still the same problem...NO BLUE!
So if is something with the monitor and not the game harness or the Game PCB.

I'll be at my shop later today and i'll try your suggestions.

Once again, THANKS SOOO MUCH FOR ALL THE INFO! Donny

[rfr341]

I agree with Kev it should be one of the transistors on the neckboard causing your problem. If you can get a hold of randy fromm's wells gardner 4900 chassis flowchart it will tell you which one is for the color blue. Unfortunatley I am not at home so I don't have the flow chart with me or I could tell you which one to check.

[DjDonnyD]

Hey RFR,
If you get a chance later, Send me that Flow chart. I won't be going to my shop it later tonite. Thank Soooo Much! Donny

[Grauwulf]

Q205 and Q208 on the main board and Q403 on the neck board are the blue drive transistors.

[rfr341]

Hey Dj, I hope the chart helped.Let me know.

[modessitt]

Worst case scenario:  Bad tube, but try the other things first.

I had a K4900 with a constant blue that couldn't be adjusted out.  After cap kits, transistors and pots, I finally hooked it up to my tube rejuv'r and found it had a short between the blue gun and the heater voltage.

So... I pulled the tube and swapped it with one from a trashed K4900 and suddenly had no blue at all!  This time the tube rejuv'r wouldn't register any readings from the blue gun.  Clean & Balance and Rejuv on the gun had no effect.  Still no blue.

FInally found another tube in the warehouse.  Put it on and had a great picture.  This was one of those rare instances where the chassis was fine.  Hopefully you'll fix it with the help from above, but if not, you may need to get ahold of a rejuv'r to check the tube for internal problems.

[SirPeale]

You couldn't remove the short with the rejuvinator on the first tube?

[Ken Layton]

Some shorts can't be removed. It all varies on a case-by-case scenario on each tube. But you can isolate it with Randy Fromm's neckboard 'trick' method.