WTB [GERMANY] 54620-61601 Logic Probe for MSO7054B - Page 1
Forum section: electronics / general

author: Nassim
author_rank: Contributor
timestamp: May 02, 2020, 04:45:50 pm
content: My second hand MSO7054B just arrived today. Now I am in need of Logic Probes for it)

author: Back2Volts
author_rank: Unknown
timestamp: May 02, 2020, 10:49:02 pm
content: Oops! I read it as a 5074 and not as a 7054 and got confused. Sorry, disregardWould something like this work for you?https://www.eevblog.com/forum/testgear/ms05000-budget-logic-analyzer-probe-set-design/

author: Nassim
author_rank: Contributor
timestamp: May 03, 2020, 07:32:51 am
content: Quote from: Back2Volts on May 02, 2020, 10:49:02 pmI dont have alot of knowledge regarding this. I have a 40Pin connector and cannot find any datasheet of the 54620-61601 to compare the specs. So i don't know if I'd trade my measuring capacity for a cash saving.

author: oPossum
author_rank: Super Contributor
timestamp: May 03, 2020, 07:44:01 am
content: The HP/Agilent/Keysight logic analyzer probes are passive. They have a compensation network in each lead.Everything you need to know including pinouts and electrical characteristics...https://www.keysight.com/us/en/assets/7018-06707/data-sheets/5968-4632.pdf

author: Nassim
author_rank: Contributor
timestamp: May 03, 2020, 02:26:30 pm
content: Quote from: oPossum on May 03, 2020, 07:44:01 amThank you i will have a look

author: MarkL
author_rank: Unknown
timestamp: May 04, 2020, 01:42:32 am
content: Also note that the ribbon cable that connects to the logic inputs on the scope is no ordinary ribbon cable. It's 16 lossy transmission lines, similar to how analog scope probe cables are made. This cable and the compensation network pictured in the previous post need to be used together for proper signal fidelity.There's a bunch of 54620-61601 sets on ebay right now, many with "Best Offer". You can try some low-ball offers. The worst the seller can say is "no".Newer versions of the 54620-61601 are N6450-60001 and N2756-60001. If you can find them, they should work too.

author: TK
author_rank: Super Contributor
timestamp: May 04, 2020, 02:06:01 am
content: Here is one low cost option that uses original HP parts (cable and POD):https://www.ebay.com/itm/254587319947Disclaimer: I am the seller

author: Nassim
author_rank: Contributor
timestamp: May 05, 2020, 06:43:04 am
content: Quote from: TK on May 04, 2020, 02:06:01 amThats what i was looking for

author: alm
author_rank: Super Contributor
timestamp: May 06, 2020, 12:44:02 pm
content: Quote from: MarkL on May 04, 2020, 01:42:32 amAre you sure it's a lossy transmission line? I know that what looks like a woven cable is actually tiny coaxial cables, but I thought it was just a plain coaxial transmission line.I just grabbed an Agilent woven logic analyzer cable I have laying around that connects to the same 40-pin pods, and the signal pins measure something like 0.05 Ohm from the pod connector to the logic analyzer connector. I think the cable is for one of the 165xx-series analyzers. So at least that one is not lossy. I could also grab a more modern cable, but since they use the same pods, I doubt there will be any difference.

author: TK
author_rank: Super Contributor
timestamp: May 06, 2020, 01:41:00 pm
content: Quote from: alm on May 06, 2020, 12:44:02 pmCan you measure a transmission line using a multimeter? Don't you need a Vector Network Analyzer or at least a Spectrum Analyzer with tracking generator to characterize a transmission line?

author: KrudyZ
author_rank: Frequent Contributor
timestamp: May 06, 2020, 05:38:37 pm
content: Quote from: alm on May 06, 2020, 12:44:02 pmI looked at one from a HP1650A under a microscope.I don't think they're using micro-coax cables, but rather signal wires separated by pairs of ground wires.There are 18 signal wires and at least 36 ground wires. There are some extra wires on the edges, which might just be there to give extra mechanical strength.Impedance is controlled by the weave keeping the wires properly spaced.Using simple wires is a lot easier to terminate than micro-coax, which is likely the reason why HP went that way.However, this makes the cable more susceptible to cross talk and I've had issues with that when the cable was draped over an area with high energy transients, like a switching power supply.

author: MarkL
author_rank: Unknown
timestamp: May 06, 2020, 06:44:17 pm
content: Quote from: alm on May 06, 2020, 12:44:02 pmOn an Agilent 54620-61601 woven ribbon cable I get 187.69R on channel 0 from one end of the cable to the other. The ground is 0.220R (maybe that's what you measured?).On an Agilent 16715-61601 coaxial ribbon cable I get 180.98R. This cable is compatible with the same flying lead probes as the 54620-61601.I have yet to discover otherwise, but I believe everything in HPAK's 40-pin probing system are electrically the same.For comparison with lossy scope probe cables, a Tektronix P6131 is 296.49R, and a P6139A is 390.29R.But I should also say that not all Agilent logic analyzer cables are lossy. On an Agilent 16760-61605 coaxial ribbon cable I get 2.391R. This cable is in the 90-pin probing family and each data path is regular non-lossy coax. These 90-pin cables have a completely different set of probes that have different compensation networks, and are not compatible electrically or physically with the 40-pin sets. They are used for probing higher speed signals.

author: MarkL
author_rank: Unknown
timestamp: May 06, 2020, 07:03:37 pm
content: Quote from: TK on May 06, 2020, 01:41:00 pmIf you want characteristic impedance, no, you can't measure that with a multimeter. But a high DC resistance will tell you if you have a lossy transmission line.For an easy way to measure the characteristic impedance of an unknown piece of cable or transmission line I like to use an LC meter. It's a good ballpark, but obviously far from a complete analysis.You can also cable together a scope and fast pulse generator to make a TDR, launch a pulse into an unknown, and analyze the return pulse.

author: alm
author_rank: Super Contributor
timestamp: May 06, 2020, 07:46:58 pm
content: Quote from: TK on May 06, 2020, 01:41:00 pmYou are right that you can't measure a transmission line with a DMM. But what distinguishes a lossy transmission line, like in a high-impedance scope probe, and a 'lossless' Z0transmission line, like RG-58 coax cable, is that the former has a significant amount of DC resistance. For example, a 1x oscilloscope probe might have a few hundred Ohm of resistance in its cable. And this is something you can measure with a DMM. So while you are not able to distinguish a lossy transmission line from a piece of resistance wire without a constant characteristic impedance, you can distinguish a lossy cable of any kind from a non-lossy cable of any kind.Quote from: KrudyZ on May 06, 2020, 05:38:37 pmInteresting, I guess they have switched. I looked at the cable for the 167xx series (16715-61601), and a slightly older Agilent-branded cable (16710-61603?), and both appear just to have 18 parallel conductors with four different color wires at the ends (presumably mechanical / ground). So my guess was that these are 18 coaxial wires for the signal pins (16 data channels, 1 clock and one 5V / other). There are too few wires for plain wires with ground wires in between. Unless there is a twisted wire pair under the molding. I'm not willing to cut open one of these cables to find out.HP say that the wires attached to the pods are twisted pair, but I have not found any official word on the cable:Quote from: MarkL on May 06, 2020, 06:44:17 pmGood point. Looking back, I did check ground and signal, but I might have been measuring the +5V line, which I'm guessing would not be lossy. I just checked the 16715-61601 and slightly older cable (16710-61603?) again with the pinout diagram, and I measure about 175 Ohm for D0 for both cables.

author: MarkL
author_rank: Unknown
timestamp: May 06, 2020, 08:07:01 pm
content: Quote from: KrudyZ on May 06, 2020, 05:38:37 pmThe two outer heavy wires on each side are for +5/GND power to external probes and demo boards. I don't know if they're generally used on the MSOs. They're certainly not supplying anything on my MSO3000X.Looks like the latest replacement for the 54260-61601, the N2756-60001, has also gone to micro-coax probably for the reasons you mention. I can't imagine it's for simplicity. I've repaired some of these micro-coax cables and they're crazy tiny.

author: oPossum
author_rank: Super Contributor
timestamp: May 06, 2020, 08:35:49 pm
content: The original woven ribbon cable...

author: MarkL
author_rank: Unknown
timestamp: May 06, 2020, 09:18:12 pm
content: I won't repost these photos to be nice to Dave's server storage, but here's a photo of the micro-coax version (16715-61601) of the cables we've been discussing:https://www.eevblog.com/forum/testgear/dsox2000-and-3000-series-licence-have-anyone-tried-to-hack-that-scope/msg1448194/#msg1448194On the other photo of the probe, it does look like twisted pair coming in. I think I saw someone else who cut theirs open completely and showed it was twisted pair. I thought I had saved mine somewhere for further mangling, but I can't find it.