I've had this NFL Blitz where the monitor was a wreck. I had to redo convergence several times and it never quite looked right. Well the other day the color green went out. Ugh.
Issue #1 Green
This isn't the first time this has happened. Green went out before and I suspected the chroma transistor. To prove it I swapped the green and red chroma transistor and lo and behold, no red. So I replaced the red transistor and we were good for a couple of years.
Now green is out again. I could just replace the transistor, technically I replaced the red transistor last time and put another old one in the green spot. Green's in the middle and on a K7500 there's a lot of heat going on there, maybe a new transistor can handle it better. So it could be nothing. But there might also be an issue downstream, so I start testing and inspecting (like an idiot). The inductors by the color transistors are looking very toasty especially green and blue. I try to take them out to compare values and the blue one just breaks in half.
I get a replacement set but mess and realize I got 10uh and 15uh values, when it's supposed to be 12uh. Does anyone know if it matters? The manual also didn't specify wattage but I figured 1/2W because there's a resistor in series with that value. I assume it's just filtering some signal and doesn't matter too much so I use 10uf and it seems fine, I eventually replaced with 12 anyway, but had to wait for that order. I also replace the green transistor and all is well. I'm done poking around, so we'll see if it goes out again.
Issue #2 Convergence
Try 1: I know very experienced people hate doing convergence, but I've had luck. I took off all of the magnets and convergence strips and loosened the yoke and was able to dial it in pretty good. I set the purity like in the manual, then adjust the yoke to perfect dynamic convergence, then tough it up with the rings. I did notice that to get red and blue convergence I had to both shut off the green signal from the TPG and turn down the green gun. Doing only one of those still had me seeing some green. I spent over an hour getting each corner perfect and putting convergence strips in just right, etc. Then I put it in the machine and there's a purity blotch in the top right corner. The degaussing coil did not help. crap. I adjusted the purity rings in the cab and how the convergence is all out of whack. I can't really adjust it in the cab because it's too hard to reach around and see the screen (I'm not a 7 footer).
Try 2: So I realize the manual said it had to face East or West when you do the convergence and I figured that was BS. This time I get it facing the right direction and go through the whole process again. Had it looking great and then once again the purity is off when I put it back in the cab.
Try 3: At this point I realize the monitor is VERY sensitive to direction and angle, it's sitting in the cab at a 35 degree angle, so I angle it in my test bench, and have it facing the exact direction it will rest in. Now I can't get the convergence to look good at all. There doesn't seem to be any angle to the yoke to make this thing look right. I know the Earth's magnetic field can effect this, but these changes seem extreme. I don't know what's going on. I wonder if there's an obstruction in the yoke or something, I look in there and it's filthy. Could it have attracted metal dust that's throwing it off? It is a giant magnet thing right? I don't know how magnets work. I consider taking it off but I know the convergence rings will break if I try because they are cheap plastic that's been baking for 35 years (and from experience!). At this point I start looking at the burn marks on the tube trying to figure out where things were when it was assembled. And that's why I realize the ring assembly is actually really loose and can slide up and down. D'oh!
Try 4: So I'm pretty sure at this point that the ring assembly moving was the issue the whole time. I take the yoke off and clean the inside with alcohol and a toothbrush anyway, that may have been a factor. Then I go through the process again with the monitor in the right direction, at the right angle, clean yoke, and the ring assembly in the correct position and Happy Christmas! I only needed 1 convergence strip this time, it came together great and only took 4 hours.
Issue #3 Vertical Line
Ever since I had this cab there's always been a faint vertical line halfway between the right side of the screen and center. Going through the Blitz monitor test patterns and such I realized that it mostly shows up on the black screen or when colors are darker. Also, even with adjusting brightness I never can get the black level to true black. You can barely see it playing but you can see it on the title screen and I know it's there. The monitor has been capped and was not seeing the line on the test bench. BUT I did notice that if I had a mostly black screen on the TPG and turned the flyback up, I did see a similar line on the left side of the screen. The K7500 is a very finicky monitor to adjust, the pots don't give you a ton of breathing room and like to be in particular spots. It also has the flyback brightness, contrast, and a sub contrast pot on the board. Does anyone know what that even is for exactly?
So anyway, the fix ended up being a combo of turning the flyback screen pot down more than I thought I needed and turning the sub contrast pot on the board up, I had to do this in the Blitz machine because the TPG just couldn't replicate it's signal. Now I have great blacks and no line! This may be partly because of the way NFL Blitz or the Seattle board outputs colors along with this particular monitor.
Just dumping this all here because each issue seemed a little bit unique and hoping this helps someone in the future.