HP 53131A & 53132A Power Off Mod

[wholder]

I recently purchased a used HP 53131A Universal Counter and was surprised to see that it's designed to stay partially powered on, with the fan running, even when the power switch is in standby.  The manual says this is for timebase temperature stability but, since I plan to use with my Trimble Thunderbolt as the 10 MHz clock reference source, I don't really need this feature.  So, I came up with a non-destructive way to modify the 53131A to have a true power off switch.  For more details, see my article at:

  https://sites.google.com/site/wayneholder/hp-53131a-power-off-mod

Wayne

[ArthurDent]

On my HP 53132A I just mounted a toggle switch in one of the unused holes for the back panel BNC input connectors and wired the switch in series with the power connector. The front panel power/standby switch is unmodified and works as usual and if I want to completely power down I can reach around to the back and turn the added switch to the off position. Much easier than the other modifications I've seen and is easily removable if you want to sell the unit unmodified.