k7000 color issue hopefully quick question/answer

bluestreak

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Noticed the blue was missing from my Race Drivin even after a recap job.
Read many forum related post's and tried the swap of RGB wires to see what happens.
Thought I had it figured out, but apparantly I'm not understanding how the color drives work (new at monitor repair).
Here's the deal:
Also see pic of current/original state.

Went into screen diags to get a color pattern and the Blue only has a straight line as in the pic.
Resoldered all joints on neck bd with no change.
Swapped the Green and Blue wires from the RGB connector on the game board output and the Green and Blue test patten swapped places with Blue still showing a line.
Figured it must be the color driver on the game board, so having a spare, I swapped the boards but no change. I know this board is good.
Sooo... Did I just determine that my CRT and game board are fine, but there remains a problem on the neck board or?
So confused.....
 

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Have you tried tweaking the blue drive/cutoff pots on the neckboard? It looks like blue cutoff is adjusted to the extreme (maybe further than possible, so there may be a problem w/ the circuit). But try adjusting those pots first.

DogP
 
Actually I did try that first. If I turned down the cutoff, blue line went away totally. (It was turned up to max).
Tried the blue adj and didn't seem to make a difference.
The adjustments are not adjustable while the machine is on because of the position of the tube and neck board, so I have to remove neck board, turn the pot, replace and turn on machine to see results.
I'm afraid of destroying the neck board or tube from too many pull off's so trying to minimize those.
So what is the purpose of the cutoff POT?
 
Swapped the Green and Blue wires from the RGB connector on the game board output and the Green and Blue test patten swapped places with Blue still showing a line.

Have you tried swapping two of the large drive transistors on the neckboard ?
Next step would be testing the tube itself.
 
Thanks for the info.
Situation is worse now as I have no video at all after disconnecting video cable and checking blue drive line continuity. Suspect a possible bad video cable but will check all wires when I can get to it again.
No I haven't tried your suggestion but will.
I won't be able to work on it again until Sunday or Monday afternoon.
Thinking about swapping the monitor board from my other unit to this one although a bit different, I think it should be compatable.
That should tell me if it's the tube or boards. Really hoping it's not the tube as it appears to be a real bear to get out.
Thanks again.
Still open to any other suggestions though.
 
How do you know the board is good? If you had a problem with blue, you'd most likely have no blue at all. if you turn up the screen control on your flyback, and blue appears where it is currently black, then we can assume the blue is weak and needs to be strengthened. if still no blue there, but still have the blue line, then I'd assume it was a problem with the test function of the board, or the wiring from it to the monitor...
 
that blue looks a little too defined and matches the other two colors at what looks to be the brightest point to be weak, IMO. if it was weak it would look like baby shit blue, not bright blue. as for the absence of the rest of the pattern, that's just weird.

I'd try an entirely different game, after confirming that (JAMMA?) your video harness is actually intact.
 
Well, only did a quick review since I really don't have the time to work on it now.
Lost high voltage, so going to replace the board with another one I have that should work, at least for testing, 1st of next week.
Man o man, Although this is just a hobby for me, how do you guys who do this for a living make any money?
 
Well, only did a quick review since I really don't have the time to work on it now.
Lost high voltage, so going to replace the board with another one I have that should work, at least for testing, 1st of next week.
Man o man, Although this is just a hobby for me, how do you guys who do this for a living make any money?

fixing things. :) you know, for other people. but IMO, coming from someone whose family runs a redemption/video game room, the only video games worth the electricity, parts and space are the ones with some sort of driving or shooting element to them.

I guess throwing games on a route can't hurt any, unless they get massively abused. at least you won't have to pay the electric bill. :)

but yeah, I think you're onto something trying a known working chassis on it, but I'd go one step easier and try another game first, if you got one or know someone with one.
 
AHHA! AHHA! AHHA!


Nice to have a semi working board to compare to.

Turned out to be a broken blue Drive POT at VR206 on the neck board.

Still not understanding why the Blue didn't work when I swapped the RGB wires from the logic board, but maybe just getting too old to understand.
Oh, and how anyone makes money at this when not just a hobby.

I think everyone was right on with suggestions as this issue was very near the end of the circuit so thanks for all of the input.

There was just know way to know of the bad POT without very close inspection or measuring, which is how I located it.

Thanks again,
Mike
 
ahoy. yeah, I've gone one step further before and swapped pots in conjunction with the transistor for colors too.

they don't fail frequently, HOWEVER, the white knob kind (which you probably have?) were made kind of shitty, the black ones were better.

same applies on the flybacks on these. white knob kind are junk, black knob kind are better.
 
Still not understanding why the Blue didn't work when I swapped the RGB wires from the logic board, but maybe just getting too old to understand.

Mike

Because doing so sent the blue signal to the red circuit and the red signal to the blue circuit (assuming that's how you swapped them). This means that what would normally be displayed as blue is now in red, and what is normally displayed in red is now blue. Except you would still see no blue (from the red signal) because you had a broken pot in the blue circuit. A bad circuit means no color. Changing the input signal will not fix a bad circuit...
 
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