As already recommended, disassemble the Ultra Hi switch and look for internal shorts between the 2 channel contact rows. If you can't repair/replace it, you can always disengage it and hardwire your preferred setting. There is a good chance this will cure your problem.And I'm in the beginning. The same behaviour like in the first post. I don't get it. I have tried to measure all the caps and resistors near V1/V2 and all looks/measures close to its specs. No bad traces, no overlapping solder joints. I have got some photos of previous work on other V4's and it PCB/wiring looks the same. I have no idea what to do now. Maybe it'll be "spare parts" V4 for some new projects.