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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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  1. #1 by Daniel B. Martin on 2018-11-14 - 08:12

    Have you any idea as to the shelf life of DeoxIT Red? I have an unopened container which has been sitting for years. Years? Maybe decades!

    • #2 by Ed on 2018-11-14 - 12:14

      What could possibly go wrong with oil? [grin]

      My squeeze bottle may become a cherished heirloom to be handed down through the generations … I think it loses more through the cracked top than in actual use!

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