34401A Multimeter Input Banana Socket Issue - Page 1
Forum section: electronics / testgear

author: rfdes
author_rank: Regular Contributor
timestamp: June 01, 2022, 02:57:03 pm
content: My early model HP34401A (red banana jacks) appears to have an issue with one of the input sockets. In particular, the 4W Sense LO socket is recessed an extra 0.180" relative to the other sockets. I've had this meter for many years (late '90s) and have just noticed this after purchasing some new Probe Master probes with the straight, retractable banana plugs. They will not mate with this oddball socket. Using a set of calipers, I measured the socket depths. Does anyone have any insight whether this can be repaired? This issue may have been present when new. If anyone would be willing to measure their banana sockets, I would be interested in the results. I am wondering if it is possible for these to be pushed backwards over years of use.Looking forward to any insight you may offer.Jim

author: bdunham7
author_rank: Super Contributor
timestamp: June 01, 2022, 03:29:49 pm
content: I just measured mine which is an all-red-socket version, but not a very early one. I was surprised to see some variance, but they were all 7.5-7.8mm, so even less than your 'good' ones. I have the Probemaster retractable leads and they work fine with mine. You'd have to open it up to see if there is evidence of the inner connector being pushed backwards. You can look at and compare the rear terminal assembly--it is the same part number as the front one. The p/n of the assembly is HP 34401-62101 if you need to replace it. Here's the manual if you don't have it.https://www.ee.ryerson.ca/guides/instrument-manuals/Agilent-HP_34401A_Service_Guide.pdf.

author: strawberry
author_rank: Super Contributor
timestamp: June 01, 2022, 03:52:14 pm
content: it is just bent copper , bend it backswap front to rear

author: rfdes
author_rank: Regular Contributor
timestamp: June 01, 2022, 04:20:00 pm
content: Quote from: bdunham7 on June 01, 2022, 03:29:49 pmI'll be damned. I just measured the jacks on the back panel and the same '4W Lo' jack is also 0.480" recessed. I guess there was a mfg error with these assemblies when mine was manufactured.Go figure!ThanksJim

author: bdunham7
author_rank: Super Contributor
timestamp: June 01, 2022, 05:45:15 pm
content: Quote from: rfdes on June 01, 2022, 04:20:00 pmThat or a previous owner had a kelvin clip set with a nonstandard or damaged banana plug and they tried jamming it in the back after it didn't work in the front and bent both terminals back inside. But a manufacturing error is possible, I suppose--just surprised nobody ever saw it before AFAIK. These meters are widely discussed, torn down and generally poked and prodded.

author: JohanH
author_rank: Frequent Contributor
timestamp: June 01, 2022, 06:14:18 pm
content: What I noticed when I got a 34401A last year was that many of my banana leads don't make a good connection with this meter, due to the recessed jacks. Some work good, some less. The rubber coating of many common leads don't fit into the outer hole of the jack due to various edges in the design and thus, the metal tip doesn't go all the way into the jack. The only ones that work good are older style banana plugs with a long metal tip (15mm+) and thin coating that fits into the hole, and straight "modern" plugs with a very thin sleeve without edges that fit into the hole all the way. My kelvin set has these straight plugs with very thin sleeves and they make good contact.

author: rfdes
author_rank: Regular Contributor
timestamp: June 01, 2022, 09:09:00 pm
content: Quote from: bdunham7 on June 01, 2022, 05:45:15 pmYes, I suppose that is certainly possible. I guess I will open it up and give it a look over. Thanks for the comments.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: June 02, 2022, 02:26:58 am
content: I have two 34401A with the newer design (black and red) jacks, so far, I have had no problem fitting any Agilent and Keysight probes into it. I also occasionally use them with probe set from other brands, and they all fit perfectly. So I wonder if it is age or use related, or something unique about the earlier all red version. Hope you are able to sort it out quickly.

author: bdunham7
author_rank: Super Contributor
timestamp: June 02, 2022, 02:34:52 am
content: Does anyone know--are these NLA from Keysight?

author: rfdes
author_rank: Regular Contributor
timestamp: June 02, 2022, 11:55:45 am
content: Quote from: NoisyBoy on June 02, 2022, 02:26:58 amI haven't opened my unit yet to see if this is repairable but I could use a stackable test lead plug as shown in the pic. These will insert further into the recess due to the conical feature where the banana mate interfaces with the plastic. My confidence is low in regards to this being repairable and i don't see wanting to change out the banana assemblies. In my opinion this is likely a mismade sub-assembly.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 03, 2022, 08:23:10 am
content: Quote from: bdunham7 on June 02, 2022, 02:34:52 amAbout one year ago, I bought this receptor block from Keysight for a 34401A and it was very difficult to get. So I assume it is no longer available for sale.

author: dreamcat4
author_rank: Frequent Contributor
timestamp: August 07, 2022, 04:55:17 pm
content: Quote from: bdunham7 on June 01, 2022, 03:29:49 pmMine is an early all red socket. And I can confirm today very similar numbers. So they seem nominal, i.e. were not pushed in at any time...my 34401a terminals depth===========================early model, all red terminals, which has the failing VFD driver ('unobtainium')front terminalsCode:recess distance from face of plastic lip to lowest edge of copper ring1. HI+ = 7.51mm = 0.296 in2. HI- = 7.34mm = 0.289 in3. LO+ = 7.62mm = 0.300 in4. LO- = 7.46mm = 0.294 in5. I3A = 7.30mm = 0.287 inplastic hole max inner diameter = 8.20mm, typical = 8.20mm = (imperial) 0.323" max, 0.323" typicalcopper ring terminal max inner diameter = 4.18mm, typical = 4.10mm = (imperial) 0.165" max, 0.161" typicalrear terminalsCode:recess distance from face of plastic lip to lowest edge of copper ring1. HI+ = 7.56mm = 0.298 in2. HI- = 7.42mm = 0.292 in3. LO+ = 7.97mm = 0.314 in4. LO- = 7.79mm = 0.307 in5. I3A = 7.36mm = 0.290 inplastic hole max inner diameter = 8.30mm, typical = 8.20mm = (imperial) 0.327" max, 0.323" typicalcopper ring terminal max inner diameter = 4.00mm, typical = 4.00mm = (imperial) 0.157" max, 0.157" typicalNot sure that helps anything, seemed like I needed to measure mine now and check how bad they were. To select the right type of jacks (for getting the probe master leads too).To check against the probe master compatibility list, and the dimensions / specs on their CAD drawings.

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2022, 05:41:24 pm
content: Those are just copper tubes - see below. Try to bend them such it fits..

author: dreamcat4
author_rank: Frequent Contributor
timestamp: August 07, 2022, 05:54:27 pm
content: yes! exactlyshouldn't be too big a deal once you can get in there. in fact Ian Scott Johnson does a great teardown / disassembly showing how to do it safely in his repair video series on the 34401a over on youtube.... in fact looking at your photo here, it seems like it might be a good idea to try jamming in an extra chunk of plastic behind the coppor tubes. To act as a spacer and block any further possible movement.Although I suppose for the safety rating they still should remain recessed by at least the 0.3" (or 7.5mm), whatever the specs calls forThanks for posting the pic dude. Very helpful

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2022, 06:08:33 pm
content: Also double-check the copper tube's solder joints at the pcb.. The tubes are simply soldered straight into the pcb.Pictures from xdevs.com