Alain found a couple oscilloscopes at a yard sale and called to see if I was interested. The Tektronix Digital Storage 100 Mhz scope sounded real interesting. (Model 2232 produced about 1990.) He bought the scope for $40. At home the trace triggered and displayed but all was out of focus and the focus knob did not go far enough in the improving direction.
I was able to download the 366 page PDF Service Manual off the internet. This manual has the description of operation and also the schematics! What a pleasant find!
On page 285 I found the focus circuit schematic.
I then took the cover off the scope and eventually found the series resistors chain on the bottom board and they were well marked. Using an ohm meter I found R890 open instead of reading 510 k ohms. Since the failure was so clear I did not even remove the circuit board to observe the failed resistor. I simply scabbed a new resistor on the bottom of the board. Remember the training (KISS = Keep It Simple Sam)?
I cut an opening in a plastic high voltage protection plate to make room for the new resistor. Now all works as designed. At least the focus is good, the traces display and the triggering works. Now to read the manual to figure out the many other features of this rather powerful scope.
Also I should replace a missing screw that holds the back cover on.