WTB: Meter adjustment screw for an HP 3400A RMS Voltmeter - Page 1
Forum section: electronics / general

author: Domokelly
author_rank: Contributor
timestamp: June 02, 2022, 11:39:47 am
content: Hi everyone,I recently purchased an HP 3400A. It looks to be in reasonable condition- but it seems to have been taken apart a few times in the past and a few parts are missing.So I was wondering if anyone might happen to have a grey plastic meter zero adjustment crew from the front panel that they might be interested in selling me?Any just in case anyone has additional parts for these- or perhaps a donor unit- I'm also after the 115 / 230 voltage selector switch from the back and the wire desk stand- but neither of these are critical.I've included a photo of mine showing the missing screw in the center of the meter panel.Many thanks and kind regards,Dom

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 02, 2022, 01:33:39 pm
content: HiThe adjustment screw is part of the moving coil meter case, you will need a complete meter case front at a minimumG Edmonds

author: factory
author_rank: Super Contributor
timestamp: June 02, 2022, 06:17:52 pm
content: Very common problem with these meter movements, you can find a donor meter front from a HP power meter, i.e. the 435A/B, not many people want them due to lack of working power sensors. The donor unit would give you the spare wire stand& voltage selector too.Edit: they use a different voltage selector, built into the power inlet.I've had to buy a few units, to salvage the meter casings & parts to repair delivery victims, with care the plastic zero part can be swapped over, from a smashed casing too.David

author: guenthert
author_rank: Frequent Contributor
timestamp: June 02, 2022, 10:21:28 pm
content: -hp- used a bunch ofsimilarMCM for various instruments. I transplanted successfully the lens of a (broken) HP400E (iirc) I got cheaply on a fleamarket into a HP419A which I received with a broken lens. They seem very much alike, but the MCM of the donor does *not* have an adjustment screw (I guess, this was deemed unnecessary for the not-so-precise AC voltmeter), hence it is now covered in my 419A (fortunately one doesn't have to adjust it all that often).I just checked, my 3400A *does* have an adjustment screw.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 03, 2022, 08:34:43 am
content: It is not clear if there is actually something missing. The mechanical zero adjustment of the meter movement is normally operated with a srew driver and should not be needed that often.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 03, 2022, 09:20:27 am
content: Quote from: Kleinstein on June 03, 2022, 08:34:43 am

author: factory
author_rank: Super Contributor
timestamp: June 03, 2022, 10:51:49 am
content: Quote from: guenthert on June 02, 2022, 10:21:28 pmThe donor you used must have been a logarithmic meter, these don't have a zero on the scale, therefore no requirement for a zero adjustor. These were an option for many of thehpAC voltmeters.I suggested the power meters as they are more of them about, than working sensors, hence why they can usually be picked up cheaply to use for parts.Beware some meter cases they may look identical from the front, but use different casing parts & the fixings are in different places.David