This was a cheap $200 eBay find, but it did have some serious problems. Obviously the glass is toast, at some point the scope test switch took a hard impact and broke the wafer. No trace on the CRT either. The power transformer in these uses hair fine copper wire for the -1300v CRT supply winding, and this one was open circuit. With nothing to lose I opened the transformer, and sure enough I saw a break in the thin wire right near the surface. It's caused by corrosion near the point where the thin winding connects to the normal size lead wire. I was able to carefully fix the break, then potted the new connection in epoxy so it hopefully never happens again. Now I had a green trace, but brightness didn't work. That wound up being a bad CRT (3RP1), must be a cathode/G1 short or something. I pulled a good CRT out of a scope I had in the garage and installed it, now brightness functions normally again. Then all I had to do was replace the scope test switch with one I picked up on eBay and it's functioning electronically fine again, next paycheck I'll order and replace the glass and the MI-3 will be perfect once again.