Some weeks ago I noticed that my scope had the #2 channel not working. It’s a Tek THS720. Nobody has touched this scope except me. Measuring the bnc connector impedance on the scope probe inputs, found that the #2 channel was at 1/2 meg ohms and the #1 channel was 1 meg ohms. Both should be 1 meg ohms. Something was up. So I took a brave step and took it apart. What makes this brave is that the scope is all solid state and portable. So it’s compact. Every step of the way I kept checking the bnc connector impedance. Right after I unsoldered the two short pieces of coax from the board, the bnc impedance went to 1 meg on the #2 channel. I could not see what the cause of this was. So after a serious inspection I soldered the coax leads back onto the board. The #2 bnc’s impedance was now at 1 meg. Sweet! When I finally got the scope reassembled, the #2 channel worked perfectly!! Man was I relieved! It appears it was just a bad solder joint. Although the solder was very nice when I inspected it.