Monitor problem- no blue

Oh well. thought I'd make another thread than take up anothers with a different problem. I haven't messed with it ni a while, but after tweeking a little though, it turns out there's no blue. The other colors work though and the blue turns out greyish usually. I've tried also toggling with the blue bias and it changes the contrast, so I guess it's not the toggle, but maybe a resistor/transistor or something. It's a Wells Gardner K7400 series I think. Any suggestions.

Often a missing drive will be dry solder joint(s) Try tapping around the CRT base with something insulated to see if the blue flashes on. If so look for cracks in the solder joints on the pcb.