Thanks to Alistair D, I got some Time/Div knob components today.
The special shaft collar from the resin remains of the
Time/Div B knob seems to perfectly fit my prototype knob. When I tried to put the
Time/Div A knob on the respective shaft I noticed that the internal shaft collar is not firmly connected to the plastic exterior. This causes the knob to wiggle. Upon decomposing the knob into its three parts (shaft collar, cap and shell) I discovered that the issue had its origin in what looks like kind of a construction error. The shaft collar, which oddly also has a 120° angle between the set screws instead of 90°, does not have a linearly grooved exterior side but a diamond pattern instead (see image). This does not allow the shaft collar to be pressed into the plastic shell without damaging it, finally resulting in a wiggly connection. At the moment I am trying to find a solution for this, without having to glue the shaft collar into the plastic shell.
With the new knob components I noticed that the shafts of the Time/Div knobs require a very high amount of torque to be rotated and the position snapping produces very hard clicks. In contrast, the Volts/Div knobs can be rotated easily. Does anybody know if this is supposed to to be like this on a D75? I suspect that the internal mechanism in which a spring-loaded brass roller rotates around a gear wheel is either set too hard or the gear wheel geometry is worn out. Unfortunately, I couldn't find a way to reach this mechanism, as the two outer circuit boards in the S2A unit do not seem to be removable without desoldering tons of wires. Does anybody know a way to get to the Time/Div switching mechanisms without desoldering half of the unit?