Fan mounts
Most of the classic Tek scopes have a fan, and most of these fans are mounted on the rear panel. In the typical arrangement, there is a yoke attached to the rear panel, and the fan motor is attached to this yoke using cylindrical rubber shock mounts. Typically these are 1/2" (12.5 mm) in diameter and 1/2" (12.5 mm) or 5/8" (15.8 mm) in height. Tektronix part #348-008 is a typical example. They have 8-32 threaded rods sticking out at both ends. The purpose of these rubber shock mounts is to prevent the vibrations from the motor from vibrating the whole scope.
The original rubber shock mounts eventually get dry and brittle and can break, leaving the fan completely unsupported, inoperable, and, in transit, the fan can move slam into delicate components inside the scope, possibly causing damage. A temporary remedy is to glue the shock mounts back together. Epoxy works for this purpose. A permanent solution is to remove the metal pieces from the shock mount, and to make a new one using plastic hose. The two metal threaded pieces should be spaced apart the correct distance by the hose, and the assembly can be epoxied back together.
Modern replacements
McMaster-Carr (www.mcmaster.com) vibration-damping sandwich mounts (part number 9376K17) have been reported to fit the purpose.
Metric parts, e.g. 10 mm × 10 mm dia. shock mounts with M4 threaded studs, will also work fine with extra washers or nuts to adjust the spacing, as shown.
Ken Chorney says:
Just wanted to add an alternative supplier for replacement fan mounts for the Tektronix 545 oscilloscope fan. Digi-Key currently stocks two part numbers which fit and work perfectly: RPC1597-ND and EAR1345-ND. Both are 1/2" length (same as original) and both have 8-32 male threaded ends (same as original). Both are slightly smaller in diameter (0.4" vs. the 0.5" originals) but this does not affect their fit at all and likely does not affect their function appreciably. I have installed three of the RPC1597-ND standoffs in my 545 and they fit and work perfectly.