I've been working on this sc-540 for a while. Replaced 4 heads. One head was questionable and I think that may have fried my head board. Red & mayenta aren't printing. It ran good test prints for 2 days, too. So close, haha. So I test the fuses. F3 is definitely gone on the head board. Before i try & solder it in I Try a 3.15 amp 250v Glass fuse and have someone hold it in place via a console fuse holder and have wires touching the fuse soldering points on the board. Once the fuse is set i turn the printer on and shuts off a few seconds after I turn it on. Everytime. Fuse doesn't fry though. Next steps anyone. I also disconnected the heads & wrap the wires that attach to the heads in card stock to make sure it's not the heads. Next i'm testing transistors on head board. Any thoughts? Anything I should be looking at as far as the main board. I do have a service manual. There are 8 transistors that relate to red & magenta or the b group. Any help is appreciated & much needed 