Steven wrote: ↑Thu Feb 29, 2024 3:03 am]
Looks pretty good to me, although the R, G, and B labels are backwards on the underside of the PCB.
How are the pots mislabeled? If you asked me to look at that picture, I would immediately point out that the pot labelled G-GAIN looks like a cold solder joint. Look carefully at the dark ring visible on the top side of the pin. I have circled it here:
In any case, if you have not already done so, go over every single joint with a soldering iron and add a tiny bit more solder to refresh it. Chances are it's something hard to see. Don't just do the pots, also do the solder joints on connectors; they get plugged and unplugged, so there is stress on the joints. Very old solder becomes brittle with time and heat, and there may be stresses inside on the joints like the weight of components and the bowing of PCBs for various reasons
If you do all that and it's still wonky, remove the pots and measure the resistance while moving the pot from side to side and make sure there aren't any significant dead spots. Often times, there develops a wear spot in the general area that the color balance is most correct, and the pots will start to act hinky in that area. If that's the case, you can try swapping the pots around to see if the problem color changes. The Gain pots should all be the same resistance, but you can confirm that when you measure them.
If all of that proves that the pots are good and the solder it okay, then it may be the output transistors on the guns or something. It's hard to say; at that point you have to go on a troubleshooting hunt, and it can take awhile for the problem to appear. Hopefully, you at least have something like a cheap component tester to check if transistors are at least showing up as probably good. The really bad thing here is that it's intermittent. That means you could have a component that will test okay, but will start to break under load and/or heat
Still, my money is on cold solder joints giving you issues. If it's not the pots, it's probably something else in the path of the blue gun