I managed to free the EXT÷10 switch through the generous application of WD-40 and moderate physical force. I can now use the other three SOURCE selections, which was my goal. The EXT÷10 switch remains extremely stiff and will probably jam again if selected, but I'm calling this a win.

There's a lot more to do on the 7B92: a stiff-to-frozen pot for the TIME/DIV VARIABLE control, and some kind of white residue on the trigger boards and the sweep selector board, spots of soot on the Peltola cables (but no evidence that anything in the 7B92 incinerated itself), some screws that need attention (one loose, the other rusted), and a broken rear frame plate to replace.

All this because I want a time base that supports ALT horizontal mode, and I like the lighted push-buttons for the delayed time base SLOPE, COUPLING, and SOURCE controls.

-- Jeff Dutky