Agilent N2744A Tek probe adapter findings + rant - Page 1
Forum section: electronics / projects

author: EE-digger
author_rank: Frequent Contributor
timestamp: November 09, 2015, 12:20:16 am
content: I purchased two of these for use at the office to use Tek P6245 active probes. Tek got these probes right, including their size and small, flexible cable. Also, they can be had on Ebay without the greed that seems to go with used Agilent probe prices. It was an amazing (and perhaps wise) event when Agilent produced these N2744A adapters. The price is right for commercial use, high for hobbiest. I think it is an acknowledgement of superiority to the Tek probe designers of the past.On an MSOX9254 (2.5 GHz), these adapters are very poorly behaved. Although the AutoProbe contacts are clean and the pogo pins have good compression, these adapters are quite flakey and unreliable. When you do get them to work, don't breath on them, less they be re-discovered by the scope.On an MSO3104X (1 GHz), same story. Very intermittent interface. Useless as they are too sensitive to movement with no apparent reason for it (i.e. clean connectors, good pogo compression, alignment, etc.)At home, interesting results and the reason for this post. I have been able to get these adapters to work nicely on a 54846A (2.5 GHz) scope BUT only with the following sequence:1. remove all probes2. default the scope settings3. cycle power on the scope4. turn scope off5. attach N2744As with probes (P6245 in this case) attached6. power scope upLow and behold, you can activate the 50 ohm terminations on the channels involved and the probes work. Only thing left to do is go into each probes settings and change attenuation to 10:1 (defaults to 1:1).The probes work great !Now the bad news. If you save the settings, you cannot restore the state that the above sequence succeeded in entering. Apparently the state we achieved is not supported by the scope application.So, if you need the probes bad enough, cycle the scope twice and enjoy !I also tried a P6249 (4 GHz probe) and it worked the same way with, of course, better rise time.Now for a rant. Why oh why couldn't Agilent support the 1152A probes on the 3000-X series ? I think another thread discussed the reduced functionality of the AutoProbe on these "lower cost" scopes. This is a poor move and dumb when you consider that they built a freakin adapter for competitors probes and don't support their own ! ! !Long live the Tek 1103 !Den

author: Someone
author_rank: Super Contributor
timestamp: November 09, 2015, 04:04:52 am
content: The 3000X has a simplified AutoProbe interface that has a fixed +/-12V and 5V supply, while the original design called for +/-12V and a +/- variable supply. Its possible to rebuild probes to suit:https://www.eevblog.com/forum/projects/agilent-probe-interface-(-autoprobe-and-probe-id)/https://www.eevblog.com/forum/testgear/tektronix-tekprobe-ada400a-to-agilent-autoprobe-mod/Even with those misaligned pogo pins it was still secure and reliable on a 3000X, but that was without having the identification/handshake/negotiation connected.The P6245 looks like a nice candidate for the same sort of modification, is there a comparable differential probe in the Tek catalog?

author: EE-digger
author_rank: Frequent Contributor
timestamp: November 09, 2015, 04:24:27 am
content: I saw the ADA400A mod and thought it was pretty clever. The P6245 is a good candidate if you don't mind modifying the probe or losing Tek compatibility. On the 54846A, this probe has good scaling and offset even without the ability to pass cal.I think Tek's nearest diff probes would be the P6247 (400MHz) and P6248 (1.7 GHz). These are larger, rectangular boxes with several slide switches on their faces.Den

author: Someone
author_rank: Super Contributor
timestamp: November 09, 2015, 05:02:58 am
content: Thanks for those they could be next on the list for my frankenstein probes. I'm not sure the 3000X drives the offset control pin, and its supply current is quite limited on the probe interface. I'll see if I can measure the voltages on a 1152A for you.

author: MarkL
author_rank: Unknown
timestamp: November 09, 2015, 05:08:19 pm
content: Quote from: EE-digger on November 09, 2015, 12:20:16 amI also use a pair of N2744A adapters on a MSO3104X, and I don't have any mechanical issues with the Tek smaller plastic compensation boxes (P5205, TCP202), or the much bigger metal ones (P6248).One thing I don't particularly like is the long and heavy lever it creates, especially with the P6248. I'm always concerned I'm going to snap the BNC connector off the MSO.And depending which Tek probes are plugged in, sometimes the MSO will shut down one of the AutoProbe interfaces on power-up, complaining about overload. The adapter then has to be removed and plugged back in.I actually prefer these older probes because through the 1103 they can be used on any equipment. As a Tek and Agilent/Keysight customer, it really rubs me the wrong way to be cajoled into investing in expensive probes with proprietary interfaces.

author: EE-digger
author_rank: Frequent Contributor
timestamp: January 21, 2019, 03:14:28 am
content: Just thought I'd update this old thread with my later discovery on the N2744A adapters.Probably a year or so ago, I discovered why the N2744A adapters were behaving badly.Upon removal of the case halves from each of the adapters, I found that two small, flat head screws which retain the PCB with the radial Tek pattern were quite loose. After tightening these screws on both adapters, the adapters were rock solid, no longer sensitive to movement, etc. The screws were responsible for centration of the PCB to the BNC jack.Now if only they weren't $500 a pop.

author: TheSteve
author_rank: Unknown
timestamp: January 21, 2019, 04:11:11 am
content: Would still like pics of the inside.

author: EE-digger
author_rank: Frequent Contributor
timestamp: January 21, 2019, 11:33:00 am
content: I blew it by changing jobs 3 months ago. But I may be buying one for myself soon. I'm in Lecroy world now at work and not loving it.

author: MarkL
author_rank: Unknown
timestamp: January 21, 2019, 05:04:54 pm
content: Quote from: TheSteve on January 21, 2019, 04:11:11 amHere ya' go... enjoy!