Wells Gardner K4600 19" troubleshooting...

I was working on this monitor, and then it got better, and then it got worse.

The original problem was an intermittent one, in which the blue would turn on full-blast and show raster lines over the entire screen, while the other colors continued as normal. So I did a cap kit, with voltage regulator and HOT replacement too. After putting it all back together, it looked pretty dang nice, with no blue problem. And then after sitting powered on in the game for a day or so, the former intermittent blue problem returned, except that it was no longer intermittent at all.

In some less-than-entirely-sane troubleshooting, I swapped around a couple of wires (blue and yellow... ) on the neck. Powering up, there was some crackling almost immediately. I didn't leave it on long enough to see what the screen looked like. After swapping wires back, there was no unusual noise, but now the screen is doing something I'm entirely unfamiliar with. I'll see a fairly random blue blinking along the entire bottom edge of the screen, and then somewhere in the right half of the whole screen there's three soft zones of color: red, green, and blue. I've never had something like this before, and so don't know what it's called to further troubleshoot it.

What on earth have I done to this poor monitor?

Blue and Yellow, sounds like those went to the yoke.

I had one of these monitors, Green on it was showing the same symptoms occasionally. IIRC we figured out one of the transistors (I think on the neckboard) was bad. I got rid of the cab before we solved it, but it seemed like swapping the transistor would have fixed it. There's a test you can do where you short pins on the transistor and note the behavior, I can't remember the details, but that test showed us it was the transistor.

Though I'd solve your current issue first.

I agree with DanAdamKOF and would recommend checking transistors on neck board. And of course reflow everything if you haven't.