Old HP 1651B Logic Analyzer cable question - Page 1
Forum section: electronics / testgear

author: Squiddaddy
author_rank: Regular Contributor
timestamp: November 20, 2020, 06:57:57 pm
content: I bought an HP 1651B Logic Analyzer a while back, and have been working on getting it running.It was missing every accessory, so I began my scavenger hunt. But it was $10, so I wasn't complaining.I got a working boot disk, and can boot the unit fine. Was able to make spares.I also got both of the jumper pods.But I cannot locate the cables to connect the pods to the unit.These are different than the ones you find on Ebay.Those are dual connectors, Pod1/2, Pod 3/4, etc.My unit only uses the single cables, one for Pod 1 and one for Pod 2.In a pinch, could I use the 40 pin IDE computer cables, or will that introduce too much noise?Or does anyone have any sources for the correct cables?Thanks!

author: oPossum
author_rank: Super Contributor
timestamp: November 21, 2020, 06:29:36 am
content: If you make your own cables then you must use the compensation network shown on page 74. The HP/Agilent cables have this in each probe lead. Using ordinary ribbon cable can work but the cable used by HP/Agilent was quite special and works better.https://www.keysight.com/us/en/assets/7018-06707/data-sheets/5968-4632.pdf

author: Squiddaddy
author_rank: Regular Contributor
timestamp: November 22, 2020, 02:52:54 am
content: Thanks for that reply.I have both of the pods and all the grabbers.I'm just missing the ribbon cables that connect the pod to the unit.It looks like a 40 pin ribbon.

author: tautech
author_rank: Super Contributor
timestamp: November 22, 2020, 02:57:44 am
content: An 80 conductor 40 pin IDE cable could be what you're looking for for better noise specs.

author: alm
author_rank: Super Contributor
timestamp: November 22, 2020, 04:04:14 am
content: The originals were either twisted pairs (the early woven cable) or tiny coaxial leads. In either case, the cables were lossy (resistive) similar to the wire used for passive oscilloscope probesI'm not sure if a 80 conductor ATA cable would be much better than a plain 40 conductor cable, since every other pin is a ground anyway. I would expect inferior signal integrity (noise immunity, crosstalk, emitted EMI, ringing) from using standard ribbon cables. Whether it's enough to cause trouble would be for you to decide.

author: james_s
author_rank: Super Contributor
timestamp: November 22, 2020, 04:07:46 am
content: It's unlikely that any damage will occur either way. Try it and see what happens, even if it's less than ideal it will probably work fine at lower frequencies.

author: oPossum
author_rank: Super Contributor
timestamp: November 22, 2020, 08:45:46 am
content: The old HP woven cables have ground and signal side-by-side. The resistance of both is essentially zero ohms.

author: alm
author_rank: Super Contributor
timestamp: November 22, 2020, 11:33:28 am
content: Is the almost zero resistance for the signal leads, or for the ground or power lines near the edge? What cable is that? I and others have measured cables from several generations of HP logic analyzers using those 40-pin pods, and all had resistive signal leads of about 170-180 Ohm. See for examplethese posts.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: November 22, 2020, 11:04:48 pm
content: Thanks for the feedback guys.I may try the ide cable to test the unit.But i will keep a lookout for the correct cables.

author: Dr.EviI
author_rank: Newbie
timestamp: November 11, 2024, 12:06:00 am
content: Hello, sorry for the necropost, but I would really like to know if you have any more photos of the internal structure of the logic probes with flexible wires?I would like to make an analogue of these factory accessories at home while maintaining the characteristics. I am very interested in what is inside the case with a 40-pin connector, and what are the differences between the pods 1...4 DATA and (letters) CLOCK.My 16702a came with E5346A High Density Probe adapters, which are great for debugging pre-production prototypes in production, but pretty much useless for the electronics repair work I do.

author: 44kgk1lkf6u
author_rank: Regular Contributor
timestamp: November 11, 2024, 01:18:00 am
content: I assume you are talking about the pod such as this one.https://bmisurplus.com/product/hp-pod-2-data-k-clock-plus-logic-analyzer-probe/The large box is a plastic frame that holds the probes together. The probes are detachable. The manual says it is to make debugging fewer signals less messy. With all the probes removed, only a plastic rectangular tube is left. The probe has 2 pins that connect to the ribbon cable. They connect to the blob of plastic via a piece of coax. With 18 probes in total, that is, 16 data, 1 ground, and 1 clock, the 4 outermost holes in the ribbon cable connector are not connected.The 2 pins plug in directly to the connector on the ribbon cable. They are signal and ground. The ground row is shorted in the connector on the ribbon cable.The part molded in plastic on the other end of the coax is the important part. It may be hard to persuade someone to destroy it to take a picture. The compensation network is between the center conductor of the coax and the single wire. It is not connected to ground. I only happen to have the service manual for the 16557D. It says on page 149:QuoteThere is no difference between the data and clock probes besides the label.The picture is from the link.