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Archive for November 14th, 2018

HP 6201B Power Supply Meter Switch Rehabilitation

The meter range switch on Squidwrench’s HP 6201B bench power supply became erratic enough to get me to tear it apart:

HP 6201B Power Supply - meter switch nut

HP 6201B Power Supply – meter switch nut

For future reference, apply a 9/16 inch deep socket after loosening two teeny setscrews in the knob.

The date codes suggest a mid-70s assembly, but the design dates back to the 60s with no plug-in anything:

HP 6201B Power Supply - meter switch in panel

HP 6201B Power Supply – meter switch in panel

Rather than unsolder eight switch leads, I wrangled it into a visible location:

HP 6201B Power Supply - meter switch rear

HP 6201B Power Supply – meter switch rear

The knob and shaft sit on a separate metal bracket held in the white plastic ring with a pair of expanded prongs. Squashing the prongs together released the bracket, so I could see both sides of the switch wafer:

HP 6201B Power Supply - meter switch front

HP 6201B Power Supply – meter switch front

Note the copious markings which would, in the event of an actual finger fumble, give me a better chance of reassembling the spilled guts. Turned out not to be necessary, but it’s good to be prepared!

The actual repair consisted of easing a drop of DeoxIT Red into each side, spinning the central switch wafer / contacts a few dozen times, then reassembling in reverse order. Re-bending the prongs turned out to be the most difficult part, eventually requiring the designated Prydriver, and ended well enough.

A quick test with a 100 Ω power resistor shows the supply was working fine and the switch produced the expected results without glitches or twitches:

HP 6201B Power Supply - test load

HP 6201B Power Supply – test load

You just can’t beat the performance of old lab equipment!

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