Cam switches

Cam switches are used in many Tek instruments, particularly in 7000-series plug-ins, but also in TM500 equipment and 400-series portable scopes.

The lobes on the rotary cam encode the lookup table of which contacts should be open or closed in each rotational position of the shaft, which is typically rotated by a knob on the front panel of the instrument. A benefit of this design is low parasitics compared to traditional rotary wafer switches.

The original idea for the]is switch type is credited to Howard Vollum - see Patent 3,562,464 Cam actuated switch having movable and fixed contacts on circuit board (Vollum, Verhoff, Sprando).

From The History and Environment of Tektronix:

So, one day, Howard said, "the plug-ins will be 5¼ inches in height."
Oliver Dalton recalls the decision to reduce the plug-in height as a traumatic one: "The decision set us back at least one year for the height decision required three major electro-mechanical component efforts in addition to the IC read-out effort: 1) new lit push-buttons ... we needed 25 on a panel; 2) cam switches - these were Howard's ideas ... we needed them to be small and reasonably cheap; 3) relays ... we needed them to be small and reliable. We then largely had to make do with other available parts, like potentiometers.

Ken Holland was involved with the development of cam switches at Tek.

For cleaning, Tek recommends swiping paper soaked in isopropyl alcohol between the contacts and pads.

Maintenance

040-0541-00 Cam switch repair kit (1970)
TekScope Vol. 9 No. 1, 1977 p.14: Cam switch cleaning tips
Tektronix cam switch repair manual

Pictures

Cam switch in 7A19
Cam switch in 7A19
Cam switch in 7A19, contact fingers (isolated from spring lever)
Cam switch with contacts on both sides of the PCB (7D15)
7D15 double-sided switch
7D15 double-sided switch
7D15 double-sided switch, bottom-side contacts
7D15 double-sided switch, through-board pins