Agilent 16720A (and 16522A) Pattern Generator Pod Schematics - Page 1
Forum section: electronics / testgear

author: DogP
author_rank: Regular Contributor
timestamp: February 20, 2022, 09:48:38 pm
content: Hey,I recently picked up an Agilent 16702B Logic Analyzer, which included the 16720A pattern generator. Fortunately, it had cables, but unfortunately, no pods. The direct outputs from the card are MECL compatible, which isn't very useful by itself, but then you connect pods, which translate the MECL to whatever level you need. There's a separate clock output, which needs its own clock pod as well.Some pods are fairly cheap on ebay, others quite expensive. If you need a whole set of them (like me), it can get pretty expensive. You can grab NOS MECL translator chips for cheap, and custom PCBs are cheap these days, so I plan to build some of my own pods (some custom pods, and maybe a couple clones of simple pods).Anyway, I picked up an original 10466A pod, which is a 3-State TTL/3.3V Data Pod. Since I plan to build my own pods, I decided to start by drawing up schematics of the OEM pod. These pods are readily available on ebay for $20-$30, so given the cost of components + time, it's probably not worth simply cloning these. But I figured it's nice to have these schematics as reference (or repairs, or just curiosity).The schematics, and pics of the 10466A board are attached. I think they're are correct (and they make sense), though I haven't built a clone from these schematics, so there could be errors... trust, but verify I guess. I also plan to post whatever other pods and 16702B related stuff I make on Github here:https://github.com/pdaderko/16702B.For completeness, I had also come across a couple good related resources... this thread discussed building custom pods, and I think the conclusion of using a SN65LVDS33 is a solid choice:https://www.eevblog.com/forum/projects/translating-differential-nonstandard-ecl-signal-to-single-ended-3-3v/This page has internal pictures of a few different pods:http://www.bitsavers.org/test_equipment/hp/logic_analyzer_pattern_generators/16522A_-_16720A_Pattern_Generator_PODs/Also, the manuals for the 16720A and 16522A describe the pods (termination, output chips used, etc), so it's worth checking those out as well.Anyway, not sure how popular these pattern generators are, but hopefully this helps someone in the future.DogP

author: inaxeon
author_rank: Regular Contributor
timestamp: February 21, 2022, 09:45:03 am
content: Good work man. I've been on the hunt for a pattern generator several times and finding one with a complete set of pods is always what's put me off.Very interesting.

author: DogP
author_rank: Regular Contributor
timestamp: February 22, 2022, 08:21:09 am
content: Thanks... yes, the pattern generator cards always seem to be pretty uncommon, and finding then with a set of cables, and especially a set of cablesandpods is never easy. This has been going on for years - when I bought my 16500A ~20 years ago, it was cheaper to buy an entire analyzer with the set of cards that you wanted, than simply buying the card alone.On the topic of cables... as I noted in the schematics, the cable is 1:1, so the pinout at the header on the 16720A card is the same as at the end of the cable. Which means if you're missing the cables and don't care about very high speeds or long cable runs, you could make your own pods that plug directly into the card and have TTL or whatever logic level you want directly out the back. Or, the cables themselves are simply 10 twisted pairs, so you could probably make your own from cheap CAT5 cable, or even make an adapter from the headers on the board to RJ45 connectors and use ready-made Ethernet cables.DogP

author: inaxeon
author_rank: Regular Contributor
timestamp: February 22, 2022, 10:51:57 am
content: Would certainly be interested to see them once they're made up...

author: fisafisa
author_rank: Regular Contributor
timestamp: February 22, 2022, 08:07:10 pm
content: HiI have just finished assembling 2 very similar pods.But I think I have spotted an error in your schematic.The input termination in my understanding is in fact one 100 ohm resistor in parallel.Not two in series. In series, if I am not mistaken, should be only 2x50 ohm resistors.From your pictures you can see that.For a second I thought I was mistaken..F

author: free_electron
author_rank: Super Contributor
timestamp: February 22, 2022, 08:30:57 pm
content: this document has schematics for all pods and cable layouts.https://xdevs.com/doc/HP_Agilent_Keysight/HP%2016720A%20Help%20Volume.pdfall the pods have a 74avc16244 in them. by just changing the power supply you can make this a 3.3 2.5 or 1.8 volt module. so if you are going to recreate the pods : make the power rail switchable ! use a lm317 and make the feedback resistor switchable.

author: free_electron
author_rank: Super Contributor
timestamp: February 22, 2022, 09:09:54 pm
content: here's my collection10460a clock pod (5 volt only)driver : 10h124receiver : 10h12510461a ttl data pod (5 volt only)receiver : 10h125 + 100ohm10462a ttl/cmos (5volt only)receiver : 10h125output driver 74act11244 + 100 ohm10466a 3-state ttl (3.3 volt)receiver : 10h125output driver 74LVTH244 + 100 ohm10483a 3-state 3.3v podreceiver : 10h125level shifter : 74CBT3244 (marked CU244). this is an octal fet switch used as zero propagation delay level shifter from 5 to whatever rail the driver is atoutput driver 74AVC16244 . no output resistors. only half of this chip is used ( this is a 16 channel device)The 16244 can work down to 1.2 volt.this last pod is the most interesting one. since they use a 1117 style regulator all they do is alter a resistor value ot make the 1.8 and 2.5 and 3.3 volt versions.this pod can be made "universal" by using a switchable regulator. (1.2 1.5 1.8 2.5 3.3 volt.)or it could be made auto sensing by using a simple tracking regulator. the pin next to the 3-state input is unused. bias that pin internally to 1.5 volt via a 1k resistor and feed it to a tracking regulator that powers the 16244. if you feed that pin externally with the right voltage the i/o driver will track what you feed.you could make a small switch (slide) that can preset to 'hard voltage' or to 'external'.

author: DogP
author_rank: Regular Contributor
timestamp: February 23, 2022, 02:28:41 am
content: Quote from: fisafisa on February 22, 2022, 08:07:10 pmCool, nice to see I'm not the only one looking to make my own pods.Regarding the resistors... I think you're looking at my schematic wrong. I've only got one resistor across each MECL_IN N and P input. They're staggered left and right simply to save space on the schematic (otherwise the designator and value would be overlaying each other, or use twice the vertical space).Quote from: free_electron on February 22, 2022, 08:30:57 pmThat doc describes the circuitry, and you can make assumptions about connections, etc... but they're not complete schematics of the pods. What I posted should be complete schematics for the 10466A (assuming there aren't any errors), which should also tell a lot about other similar pods.And yep, I plan to build a pod with a jumper adjustable feedback resistor for a multi-voltage pod. I'll probably use a standard level shifter IC though (instead of the 16 output 74AVC16244). Though all pods certainly don't have a 74AVC16244... the TTL data pod is the simplest of them, which is basically just a couple 10H125s.Nice pod collection though!DogP

author: fisafisa
author_rank: Regular Contributor
timestamp: February 23, 2022, 07:34:40 pm
content: You are right I did not read your schematics correctly.F

author: fisafisa
author_rank: Regular Contributor
timestamp: March 02, 2022, 01:42:59 pm
content: Hi.I was checking your git repo and I discovered you are doing as well a backplane extension.My question is whether it works.In fact I was looking into a solution but I was afraid of using cables in case there were too much voltage drop.I was also worried about signal integrity.Great jobF

author: DogP
author_rank: Regular Contributor
timestamp: March 03, 2022, 02:12:56 am
content: Yes, actually I posted about it in this repair thread over here:https://www.eevblog.com/forum/repair/series-defect-on-agilent-167xx-boards/msg4031926/#msg4031926.It seems to work, at least from the quick testing that I've done with it. I'm not sure how long of a cable you can use before running into problems though... the 17" cables I'm using seem OK. Further up in the thread I built a really quick extension with just a couple IDC connectors and a 9" cable, and used that a lot without problems while troubleshooting several cards. I was able to get all my cards fixed before the new extensions arrived, so I haven't had a need to run them for long periods of time.DogP

author: fisafisa
author_rank: Regular Contributor
timestamp: March 05, 2022, 07:15:44 pm
content: HiI have a broken 16720 and I am trying to fix it.So I am going to build something like yours.Thanks

author: Halberd
author_rank: Newbie
timestamp: September 10, 2022, 02:28:46 pm
content: Oh, if I had known the information here earlier, my difficulties would have been reduced.Thanks for the circuit info. I plan to make a POD as well.I will upload a photo of the LVDS POD.

author: aeg
author_rank: Regular Contributor
timestamp: November 18, 2023, 05:48:33 am
content: 10472A 2.5V clock pod10H124, 10H125, 74AVC16244, 74CBT3244, LT1117, BAV99

author: aeg
author_rank: Regular Contributor
timestamp: December 02, 2023, 06:18:23 am
content: Assembled pod overall dimensions are 3.580"x1.840"x0.650" including projections. PCB measurements are attached.

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 14, 2024, 07:42:14 pm
content: So I have started working on this effort as well since I don't want to shell out 1000+ for a full set and think I have made some progress. I'd love some feedback here, particularly on the 10473A/10476A/10483 schematic since I am not entirely sure how the 74CBT3244 is being used as a level translator here.Unfortunately I do physically posses any of these pods, so I have no way to do a continuity check to see if I have wired up my designs correctly.I'm not planning to really bother with the 10468A, 10469A, 10470A, or 10471A since I do not have any use for PECL and LVPECL. I would like to have a set of these to just have a complete set, but it is proving difficult for me to find a source for the chips used in these pods. I have been able to track down a source for every other chip except for these.EDITED: added schematics for E8141A and 10462A

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 15, 2024, 09:19:46 pm
content: I'm now starting to doubt my wiring for my 10473A/10476A/10483 schematic due to not being sure how the BAV99 is being used here. For anyone who owns a 10473A, 10476A, 10483, 10472A, 10475A, or 10477A I'd love if someone might be willing to do a few continuity tests to determine what pins the VCC and GND of the 74CBT3244, 3 pins of the BAV99, 3 pins of the LT1117, and VCC and GND of the 74ACV16244 are connected to. I think there might be some fun little tricks going on with the power rails here, but I don't own any of these six pods to verify that for myself.

author: deanclaxton
author_rank: Regular Contributor
timestamp: March 15, 2024, 03:43:27 am
content: Subscribing to this thread as I'm on the hunt for a 16720A pattern generator and there is a fair chance when I find one (at a reasonable price) that it won't come with pods.

author: ZGoode
author_rank: Frequent Contributor
timestamp: July 26, 2024, 10:50:39 pm
content: I just got my hands on a 10473A 3-State 2.5V pod which means I should be able to reverse engineer the last few schematics that I haven't done yet