Where to find a new power switch for a HP3478A? - Page 1
Forum section: electronics / repair

author: Harfner
author_rank: Contributor
timestamp: September 01, 2018, 09:42:27 pm
content: I got a HP3478A right out off the waste bin.The power switch is broken, it does not stay "on", so I have to press it continuously to keep the device working. Obviously not a long term solution.Does anybody know, where to get a new switch? Preferably in Germany or at least in Europe. Shipping cost from the US is probably much too high.Otherwise, the HP3478A seems to work, at least it passes self test.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 01, 2018, 10:33:50 pm
content: The power switch has a small piece of bent wire that is the toggle device that is held in place by the spring that also pushes the switch lever and button back out when you release it. I picked up several 'broken' HP 3478A multimeters and a couple of them had a similar problem. What I found on one was that the heatshrink covering the switch terminals was too far toward the front of the switch and over time started rubbing on the small wire toggle device and prevented it from going into the latching position. The second one was just a little dirty so I brushed the dirt and dust off and applied a small drop of light oil on each end of the metal toggle. Both switches worked fine after the repair. If you're careful you can probably save the switch you have.

author: Harfner
author_rank: Contributor
timestamp: September 02, 2018, 02:39:12 pm
content: Thank you very much.I tried following your advice and realised, the things are even simpler in my case: the toggle device is working! It's just the key cap broken/missing, meaning I have to press the power button with a screwdriver to reach the toggle point.This allowed me verify that at least 3V and 30V DC is working correctly within spec. A 10k resistor also gives a plausible value.So I have to ask: Where do I find new key caps for the power switch and for the front/rear switch?

author: Terry01
author_rank: Frequent Contributor
timestamp: September 02, 2018, 02:46:37 pm
content: There is a post on here somewhere where a guy has loads of spares for HP Tek etc machines. I think he came across a rack of spares somewhere. He has everything numbered so just a part number and he can tell you if he has that part or not.I'll see if I can find it for you,,,,

author: Terry01
author_rank: Frequent Contributor
timestamp: September 02, 2018, 02:51:11 pm
content: https://www.eevblog.com/forum/buysellwanted/fs-new-test-equipment-repair-parts-hp-agilent-tektronix-fluke-etc/msg1238752/#msg1238752There ya go... worth a mail to see if he has what you need! Good luck!

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 02, 2018, 04:19:40 pm
content: If you have a 3D printer, you can give this button I made a try.I haven't tried it myself yet, so if you do print it, let me know how well it works.

author: Bratster
author_rank: Frequent Contributor
timestamp: September 03, 2018, 04:33:27 am
content: Quote from: TERRA Operative on September 02, 2018, 04:19:40 pmThanks for posting that, was able to replace the broken button on the front/rear switch on my 3478.I did have to shave down the little locking tabs inside that cap, and it still took quite a bit of force to push on so I removed the linkages from the meter to be able to apply force safely.Sent from my Fi Moto x4 using Tapatalk

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 03, 2018, 01:16:02 pm
content: Nice.I'll modify the 3D file a bit to compensate.Can you post a pic?

author: Bratster
author_rank: Frequent Contributor
timestamp: September 03, 2018, 05:38:29 pm
content: Quote from: TERRA Operative on September 03, 2018, 01:16:02 pmHere you go.Now just to replace the Rifa caps...Sent from my Fi Moto x4 using Tapatalk

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 04, 2018, 02:11:24 am
content: Looks good!

author: Harfner
author_rank: Contributor
timestamp: December 01, 2018, 03:05:41 pm
content: Hello, I finally found the time to test the button caps a German fellow provided just for material costs. Like Bratster wrote, I had to widen the inside with a file/rasp?, otherwise I could not fit the cap.I replaced the ram battery as well, which probably was original from 1986. So I finally had a justification for buying the isolation transformer some time ago.Many thanks to TERRA Operative for providing the 3D-model.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 01, 2018, 04:17:28 pm
content: Here's a new version with a bit more clearance inside.Might help to fit better for future prints.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: January 06, 2022, 03:02:18 pm
content: Did anyone print this with resin printer?