Agilent 1156A Teardown - Page 1
Forum section: electronics / testgear

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:30:40 pm
content: I recently bought an Agilent MSO7104B and took a chance on buying a probe on eBay that ended up being a dud - it was stuck on 25 volts indicated output and the business end got warm. I have this idea to build some 1GHz probes of my own and, initially I may reuse parts of the dud 1156A but I'll post that separately.I contacted Keysight to ask about a repair but they quoted me $1,569 which is crazy considering that the recommended replacement, an N2795A 1 GHz active probe lists at $1,050So I decided to do a teardown. First the bit that plugs into the Autoprobe interface on the scope...

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:33:01 pm
content: I removed the plastic bayonet locking device and then took the BNC assembly out of the housing.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:34:58 pm
content: Next we unplug the PCB and look at the reverse side of it

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:36:38 pm
content: Another view of the PCB top side and the housing it fits into. That spring-pin assembly comes out if you push the pins in and then carefully lift the inside edge

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:38:14 pm
content: Then I looked inside the business end using a microscope (it's small) - here I think we get an idea of why it doesn't work.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 06, 2016, 05:39:34 pm
content: The business end electronics fit inside a small brass shell shown in these pictures..

author: _Wim_
author_rank: Super Contributor
timestamp: February 07, 2016, 06:51:24 am
content: Nice pictures! Very interesting...

author: TiN
author_rank: Super Contributor
timestamp: February 07, 2016, 07:07:30 am
content: Did you try putting back missing capacitor? It might be OK after all (if gold bond wires are intact).

author: edpalmer42
author_rank: Super Contributor
timestamp: February 07, 2016, 07:47:26 am
content: The two resistors on the end are laser-trimmed. I can't tell if they're blown or not. Compare the picture of the tip with the one on this page:http://willhb.com/2014/07/agilent-active-probe/. They don't look that different.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 07, 2016, 08:52:08 am
content: Very impressiveIs keysight offering parts for this, if you are repairing it yourself?

author: TheSteve
author_rank: Unknown
timestamp: February 07, 2016, 09:28:18 am
content: Indeed, get a capacitor installed.

author: crispy_tofu
author_rank: Super Contributor
timestamp: February 07, 2016, 09:49:21 am
content: Very cool.

author: TinkerFan
author_rank: Regular Contributor
timestamp: February 07, 2016, 09:55:28 am
content: Really nice picturesI know Shahriar (TheSignalPath) made a teardown of an InfiniMax III N2802A 25GHz probe a while ago. There might be some useful information for you in that video and if not, it is still very interestinghttp://thesignalpath.com/blogs/2015/09/05/teardown-analysis-of-a-keysight-infinimax-iii-n2802a-25ghz-active-probe/

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 07, 2016, 09:57:49 am
content: Quote from: edpalmer42 on February 07, 2016, 07:47:26 amSo this one is missing one cap and the other one is missing another one. What's the deal here? Do the caps just fall off or are they not installed at the factory as a part of some sort of trimming process?

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 07, 2016, 01:29:00 pm
content: Quote from: HighVoltage on February 07, 2016, 08:52:08 amGood question. I contacted Keysight and got a quote for repair... $1,569 which is more than the $1,059 list price of the N2795A 1GHz active probe that is the 1GHz recommended replacement. The people I spoke with agreed that it seemed wrong but were unable to persuade anyone to alter the price.I will try replacing the capacitor - it's worth a try.Thanks for all the positive remarks about the photos, believe it or not I looked around for my 14 Mpixel Canon but couldn't find it so I took the pictures using my iPhone 6+

author: edpalmer42
author_rank: Super Contributor
timestamp: February 07, 2016, 02:39:10 pm
content: Quote from: HAL-42b on February 07, 2016, 09:57:49 amConsidering how small they are, maybe just dropping the probe could break off a capacitor. Something like a conformal coating would help to hold everything on the board.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 07, 2016, 03:23:24 pm
content: Just looked at the head unit under the microscope, there are 2 wire bonds broken at the top side of the bare die package so I'm basically giving up on the repair. I think I'll try to hook up my new home brew FET probe to the scope end of this lead and take power supplies from it too.

author: Neganur
author_rank: Unknown
timestamp: February 07, 2016, 03:53:46 pm
content: Any chance you could post that last probe shot? I wonder if that could be fixed with the right tools (bonding machine here)

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 07, 2016, 11:44:38 pm
content: Quote from: Neganur on February 07, 2016, 03:53:46 pmThanks for the offer but I cut the coax cable off already