wells 25" k7131 color issue

al_dunn

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I have a WG 25K7131, it has RGB, but I cant dial the colors in correctly on the test screen of golden tee, Ive tried both a golden tee 97 and 2k board with the same results so im ruling the board out, the pots let me adjust everything without a problem and seem to be working as they should but, I dont get colors such as orange, purple and brown. Ive tried the pots in several different arrangements but cant seem to dial in the colors. I have installed a cap kit on monitor once I got it because of the color issue, and its just basic practice for me on older monitors, ive checked solders, connections etc. I did notice some leakage (hot glue looking material) on the flyback brightness knob, but wasnt sure if that was causing the issue, I will probably replace it due to the leaking however, The Screen at has a green/bluish tint at best. Any recommendation on color adjustments or possible causes.
 
It's hard to determine what's up, if a tube has for instance a weak Red gun, you can still get red, but the intensity of it isn't right. You can turn the whole screen red, but you can't turn it back down to get a nice black... AND a nice red where it's supposed to be.

Problems like that though too can be in the color circuit on the board. It's kind of tough to track down sometimes, I had one yesterday driving me crazy, same thing, the blue was tripping and I was sure it was the tube, then it ended up being something on the neckboard.
 
so i bought a cheap donor tube a 27" older zenith tv ($10), and swapped the tubes out, but im still getting the same color issue, I have all colors but the color just isnt right, I even went as far as swapping out the wiring harness to the pcb with a new jamma harness I had laying around. So the problem is obviously in the chassis, what should I be checking for besides the obvious solders, part burns, etc.
 
interesting. you went from a 25" tube to a 27" ?

"nonono" in 3, 2, 1...

honestly though, I don't think caps will contribute much to this, but has the chassis been recapped? the places to look would be on the neckboard. there will be 3 transistors, one for red, green, and blue. corresponding adjustment pots go with them too, I think there's a red and green drive, and then there will be a red, green, and blue bias pot.

depending on which color is missing will be where you want to look. I think you can follow the traces from the transistors to the pots to figure out which color's which (they're typically laid out in the same order of the pots, like red, then green, then blue.)

one handy check is to desolder those transistors and move them around. if one primary color comes back, and another gets lost, you're looking at a bad transistor. sometimes you'll get lucky and all 3 work again though, because there may have been poor solder work done previously, or they solder needed to just be redone on them. these K7000s are like 20-25 years old in some cases, so that's to be expected IF they've never been worked on before.

next approach would be a cap kit, if you get the color issue sorted out. caps do in fact improve the image quality a lot on these K7000s.

oh, and I'd go back to the old tube, or at least another 25" heh. you'll probably find now that the whole screen can't be filled.
 
I had this on a K7000

And I just had to resolder the pins on the chassis where the connection comes in for the game. The red one in my case was loose. After that, all colors were great.

Keep in mind I was still getting red. It was, as you say, just not right.

Maybe you did this, maybe not, but these things are notorious for the solder on these pins.
 
And I just had to resolder the pins on the chassis where the connection comes in for the game. The red one in my case was loose. After that, all colors were great.

Keep in mind I was still getting red. It was, as you say, just not right.

Maybe you did this, maybe not, but these things are notorious for the solder on these pins.

oh yeah, I forgot about the header pins. lol *I* never had this problem on the 3 K7000s I've worked on, but it's a common complaint, and like I said, these monitors are pretty old they're gonna have cold solder in places.

there was a way to ground the color transistors, one handy way of determining if they work or not... just alligator clip the top of the transistor base on the heatsink to logic ground, and you should get a solid screen of whatever color it is. do all 3 and you should get a white screen.

if you happen to get red this way, then your issue would then be narrowed down to the input header pins or the game board itself (which could alternatively be a problem in the JAMMA wiring and/or the video signal connector itself).

^ troubleshooting.
 
Please post a pic of the screen issues and also a pic of the video connection of possible.

I have a couple ideas but its kind of hard to go on blind if that makes sense.
 
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