Agilent 1147B current probe, (2013) Repair, (FIXED) - Page 1
Forum section: electronics / repair

author: HighVoltage
author_rank: Super Contributor
timestamp: September 07, 2015, 09:47:35 am
content: ThisAgilent current probe 1147Bwas a bargain because the cable is broken / cutI want to repair it, if possible.But, before I open it up, I want to ask here, if someone might have taken this probe apart before and what to look out for.What are the traps?Obviously, the cable will not be available from Keysight.So, my first thought was to just use the longer part of the two cables and reconnect it.This will most likely have an influence on the dynamic range and calibration of the probe but for low frequencies it should work, I guess.Or are there any other suggestions of how to proceed.Inside the shielded cable there are:1 x Coax, looks like RG316 size5 x small cablesAlso, does anyone know of an existing Service Manual for this probe?Any ideas or advise is welcome.Thanks

author: acbern
author_rank: Frequent Contributor
timestamp: September 07, 2015, 01:47:41 pm
content: Well, I would just give it a try and check if this works (i.e. meets spec) with the longer cable reconnected. I would not change the cable against another one in the first place, only as step two if it does not work. I would anyway be surprised if such a small change makes a big difference. If you want I can check it thereafter. Send me a PM in such case.Not even sure if the cable is not available (unless you checked, i have not, somtimes spare parts lists at Agilent/K. are a surprise.I have not found a service manual for this one.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 07, 2015, 02:28:30 pm
content: Thank you acbern,No, the cable is not available from Keysight.The only replacement part they are offering for the 1147B is the 50 Ohm current loop (N2774-23801) for only Euro 1269OK, thanks for the advise.I will connect all the wires, to see if the probe works at all.If it does work, I might get a good quality coax coupler and put the broken part in to a small metal housing

author: HighVoltage
author_rank: Super Contributor
timestamp: September 07, 2015, 03:52:33 pm
content: Ok, here is my first attempt, just to check, if the current probe is working, when all the wires are connected.Excuse the crude looking connection, it is just for testing purpose.And ... the result is perfect for this relative slow signal.This is an inductive load current, measured on my Agilent MSO7054B Scope.Compared with another probe hooked up to a different scope, this 1147B is right on.So, now I need to find a good small connector to connect the coax correctly.Probably best to put this in a small shielded box, may be not so easy to find one.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2015, 04:49:36 pm
content: I guess the colorful wires only transport dc voltage,offset and so on.. no harm in performance no matter how rude u reconnect them. but you need to put your available skills in reconnecting the coax.i suggest use small copper tube as shield with even distribution surrounding it of soldering the existing copper shield strands.heat shrink (dielectric) as covering the signal line. do it as short as possible to minimize transmission impedance discontinuity disruption as much as possible. that maybe you need to redo the above picture by cutting small length all of them and redo, you can do better. larger outer copper tube to shield all wires. i dont know the BW and how that thing costs in new condition.if its thousands then its worth putting all your soldering and covering kungfu into it incl the dc wires. characterize it,if its acceptable, pot the area for eternity.

author: SeanB
author_rank: Super Contributor
timestamp: September 07, 2015, 05:59:32 pm
content: Cable like that is easy yo just repair, using some heatshrink tubing. first you place 2 pieces of heatshrink, preferably an adheasive lined type, over the outer to do the final shrink seal. then you n you join the small wires with solder and put a small shrink tube over each joint to protect them. Then sgrink the small sleeves. Coax you solder the inner and cover with PTFE tape to protect, then use some braid from another cable, slipped over before along with some heatshrink, to remake the shield around the whole screened cable, using the heatshrink to protect it. Finally the outer braid has the same done to it after wrapping the inners in PTFE tape. Then you slide the outer shrink over and shrink it to cover the lot, and the second tape ( longer than the join by around an inch each side) then seals the lot.Done it a few times, just is a little fiddly on really small cables or those with multiple coax cables.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2015, 08:10:59 pm
content: Quote from: HighVoltage on September 07, 2015, 03:52:33 pmHell, thats quite neat.I'd be tempted to carry on with that, insulating the coax inner, provide a better connection for the 2 braids then wrap with copper foil tape and finally shink sleeve.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 08, 2015, 10:55:02 am
content: Thank you all for the suggestions.I had to do it twice, my first attempt was not neat enough for me and I did not have the correct braiding last night.So, this morning I got some braiding in the right size and made another attempt.There are probably still improvements for a "next time" but so far I am happy with the results.Especially since the probe works perfectly on my 7000 series Agilent scope and is detected perfectly as a 1147BHere are some pictures of the highlights of this step by step.It took about 1 hour to get it assembled.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 08, 2015, 11:03:37 am
content: Oh, I forgot to post the braided tubing.It is a flat type that does not fray out at the ends, about 6.25 mm wide.

author: MarkL
author_rank: Unknown
timestamp: September 09, 2015, 12:23:54 am
content: Nice repair!

author: HighVoltage
author_rank: Super Contributor
timestamp: September 11, 2015, 04:07:14 pm
content: Quote from: MarkL on September 09, 2015, 12:23:54 amThanks MarkLFor completeness, I had the 1147B calibrated by an official DKD, DAkkS laboratory with certificate.And it was completely in calibration, no adjustments needed.At the same time I had my 1147A current probe calibrated.Almost no difference on my scope, pretty amazing, how stable these probes are.Also interesting, the 1147B is labeled to 50 MHz (-3dB) but in reality it has only -2dB at 50 MHzThe second scope picture shows both curves over each other, in an almost matching fashion.I am pretty happy with the outcome of this repair.

author: nctnico
author_rank: Super Contributor
timestamp: September 12, 2015, 03:45:03 pm
content: Hmm. I recognise that prober from Ebay; you still paid a lot for it! I made some offers but the seller declined. Good to see the probe still works!

author: HighVoltage
author_rank: Super Contributor
timestamp: September 12, 2015, 04:16:33 pm
content: Quote from: nctnico on September 12, 2015, 03:45:03 pmYes, it is from ebay China and was shipped by free DHL Express and arrived in 3 working days.At first the seller did not accept any of my offers, as you said.But then I made several extreme low offers from other ebay accounts and then the seller was finally happy to accept my offer and I got it for a bargain price, since it is working.