I wondered if anyone had any thoughts on what must be a fairly common occurrence with vintage HP equipment featuring the ‘Bill West’ leaf spring switches?
In what’s now become my standard procedure, before doing much else on a newly-acquired HP 3456A bench voltmeter I removed the front panel and unscrewed the PCB with its 37 Bill West switches. The state of the switches was worse than I’d ever encountered before: some completely floppy, some dead stuck, some graunchy …. On inspection, some of the leaf springs had popped out of the tiny ridges at either the plunger (white) or body (red) end, all were rusty and caked in dried-on old lubricant, just about all had a distinct kink at the plunger end, and worst of all 4 were missing altogether.
I started the laborious process of extracting them all, cleaning the springs in an ultrasonic bath and cleaning the switches with IPA. Meanwhile I mechanically deconstructed the instrument pretty much entirely, down to subchassis level, which revealed one of the missing springs near the lip of the front panel housing, and another which dropped out onto the floor from an unknown location. The other two were nowhere to be found, although I can easily make replacements for them (I posted on this separately a while ago).
But it’s still a big worry to me that in such an instrument there are probably two small pieces of bare metal floating about somewhere, potentially able to cause chaos or worse, danger. I suppose they might have been lost when it was opened for a previous repair, as it clearly had been, but then again maybe not. Does anyone else have any thoughts / experience on how to proceed, other than to hope for the best?
Thanks as always for any help.
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