What's the Deal With This Wells K7400?

Fatsquatch

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I'm trying my best to fix the chassis in my newly acquired Off Road Challenge (instead of buying a replacement), but it's being difficult.

When I got the game, it had good color, but the picture was all stretched in the top half of the screen and the image wasn't all that sharp. I performed a full cap kit and replaced the resistor at location R811, but now the monitor has next-to-no-color, and seems dim. The image stretching issues I originally had are gone and the picture is sharp, but no matter how much I adjust it, this is as good a picture as I can get out of it. (See pics)

Any idea as to what's going on here?
 

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Yes, sir.

I've adjusted the picture with the Screen and Focus on the flyback, as well as the 5 pots on the neck board.
 
what's the chance you have a spare neck board to exchange with this one? any 719 board can be used...if you have done a proper cap kit I would consider looking at the IC on the neck board as a possible problem....as long as all the connections are good.
 
Sadly, I have no other neck board on hand.

I may have to hit up some local pals for one to try.

Thanks, all!
 
Personally, I think you fucked up putting the 811 in. Either wrong value, or bad solder, because that's what they look li,ke when 811 is messed up. I also think that may be it since you said it had good color before you did the capkit and replaced 811.

Try checking resistance from the pad past one end of r811, to the pad past the other end of r811 (so that you're measuring all the way through both solder joints onto the board). If the resistor is fine, you should get a resistance, even on the board, of less or equal to whatever the value of the resistor is. If you get an open reading or a high reading, check your solder joints.
 
Sorry, Lyon...I worded my original post poorly, as I replaced the 811 because of this issue -- not as some preemptive measure.

With both the original resistor and the replacement, the monitor looks the same. (I've triple-checked, and the solder joints are good on that resistor.)

Following cadillacman's suggestion, I'm wondering if the problem lies on the neckboard:

25" K7400

Symptom: Monitor would not sync and what picture I can see looks like it's only showing the blue.

Diagnosis: Tracing back found a bad Z700. Replacing it gave me proper sync, but only the blue part of the image. Swapping on a new neckboard fixed the issue, so the problem was definitely on the neckboard. Found the Red drive transistor (Q505) to be bad, but replacing it did not bring back red. Found Q510 and Q511 to be shorted. Replaced them and all colors were back.

Solution: Replace Z700 and R600 to fix sync issue. Replace Q505, Q510, and Q511 fixed color issues.

I definitely have a tiny bit of blue in the picture, but that's about it. I don't know why the neckboard decided to develop issues after the cap kit, but Mod's description above certainly seems like it applies.
 
the 7400,7500,u5000 are pretty well known for solder issues on the neckboard, the color drive transistors run so hot that eventually they unsolder/birn themselves right off of ther board.


It could be that when you had it off you bumped one or two of the transistors breaking the little bit of solder left connecting them.. Id definitely give it a once over for crappy solder joints and see if you get lucky.
 
Yes if you replaced r811 to try to fix it and that didn't, I'd go with what caddypimp said, the neckboards get so hot that the transistors and resistors will fall off :)
 
the 7400,7500,u5000 are pretty well known for solder issues on the neckboard, the color drive transistors run so hot that eventually they unsolder/birn themselves right off of ther board.

It could be that when you had it off you bumped one or two of the transistors breaking the little bit of solder left connecting them.. Id definitely give it a once over for crappy solder joints and see if you get lucky.

Yes if you replaced r811 to try to fix it and that didn't, I'd go with what caddypimp said, the neckboards get so hot that the transistors and resistors will fall off :)

That definitely sounds like a plan.

Thanks a bunch, guys! I'll let ya know how it turns out.
 
The solder joints definitely looked dodgy on the neckboard's transistors, so I reflowed them. Sadly, it made no difference. :(
 
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