HP 16534A triggering problems


One of my HP 16500B logic analysis systems has a 16534A digital oscilloscope module installed. The module has a great specification: two channels, 2Gsamples/sec, 500MHz analogue bandwidth, and 32k record length. I would find it a really useful debugging tool, if it worked properly. Sadly it doesn’t.

Though it displays a trace successfully, and the controls work, it won’t trigger. The only way I get a trace is by auto-trigger. In this case the trace isn’t synchronised, so it’s impossible to catch a particular event at a particular time. Here it is displaying a square wave (well, it’s nearly square – I hadn’t adjusted the probe compensation so it’s a bit curvy on the top and bottom). Adjusting the trigger level just doesn’t make any difference.


The service manual for the 16534A isn’t very helpful. It describes roughly what the self-tests do, and how to run the self-calibration procedure, but has no detailed circuit information. The self-test reports a ‘D/A’ failure:

DSC_0405and the self-calibration procedure fails on the Trigger and Hysteresis sections:


The service guide describes the D/A test like this:

Test DAC This test verifies the correct operation of the D/A convertor on the board.
Both the offset and trigger level D/A convertors for each channel are set to a reference
level and then changed. The logic trigger IC is programmed to detect the changes. The
detection of a correct trigger indicates that the D/A convertor is operating normally.

It seems clear that the offset D/A converter is working, since the offset control works and moves the trace up and down as it should. However, the trigger level control doesn’t seem to be doing what it should. I had a look at the board, looking for components likely to be the DAC or trigger IC. Unfortunately, the semiconductors on there seem to be mostly either standard ECL logic, trivial things like op-amps, or magic custom HP chips with dozens of pins. One exception was this:


It’s an AD96687 from Analog Devices, which is a dual high-speed comparator with ECL outputs. If I was designing a high-speed trigger circuit using 1994-vintage components, I might use a device like this. I’ve had a look at all its pins with the power switched on and a signal applied and tests running, and none of them seem to change at all. One noninverting input is stuck at +5V, and the other inputs are near ground. One set of outputs isn’t even showing valid ECL logic levels, but it may be unused and thus have no load resistors on it.

Maybe it’s a red herring and nothing to do with the triggering at all, but I’m suspicious that I never see anything change. Without more circuit information, it’s hard to get much further, sadly.



30 thoughts on “HP 16534A triggering problems

  1. Brandon Dillon

    Hello Martin,

    I stumbled across your website when I was researching a few questions on the HP 16534A board. I am trying to use the board for a data acquisition project without the accompanying 16500 mainframe. I’d like to find a pinout of the backplane connector and instruction list so I could emulate the CPU board with a full computer.

    You seem to have quite the handle on digging around inside the 16500. Have you come across anything like this?


    1. martinjonestechnology Post author


      Thanks for noticing the website! I’m afraid I don’t have any pinout information on the backplane connector or its signals, and have never seen any schematic diagrams for the 16500 series boards. I believe HP has such things as CLIPs (Component Level Information Packages) and I’d dearly like one for my sick 16534A, but I’ve never seen any, I’m afraid.


  2. John

    Hello Chris. I also came across your web site when doing a search on the HP 16500-B main frame I have with the 16530 & 16531 scope modules. Do you happen to have any info about the interconnecting ribbon cable? That was missing with my modules. Thank you.

    1. martinjonestechnology Post author


      Thank you for your message. I’ve also got a 16500B with 16530 and 16531 modules. There is one 16530 and three 16531s. The interconnecting cables between them are nothing special – just 10-way ribbon cable with normal IDC headers at each end, No screening, no coax, just standard grey ribbon cable. I believe these are the original ones because the machine the boards came out of still had its calibration stickers intact.

      I hope that helps.

      1. John

        Hi Chris. I finally got around to purchasing some ribbon cable and IDC headers, put them in and the oscilloscope seems to be working just fine. Thank you for the recommendation.

  3. Antonino

    Hi Chris,
    im also in trouble with a 16534A.
    The problem is the same.
    I tried to replace nvram without results.
    Any news?

    1. martinjonestechnology Post author

      I wondered about that but looking at the pins of the AD96687 nothing seems to change when I adjust the trigger level or apply an input signal, so I doubt that the AD96687 itself is faulty.

  4. Antonino

    Just a little news…
    Im testing the board in 16702A main frame.
    All test passed.
    Test Fiso OK
    Test ADC OK
    Test DAC OK
    Test logic Trigger OK
    Test Timebase OK

    Of course the problem is still present.

  5. Antonino

    Moreover in 16702A calibration procedure Hysteresis is OK.
    Only fail Trigger Level, Trigger Delay and Logic Trigger.
    External Trig Skew is also OK.

      1. Antonino

        Not so important but External Trigger I & O are connected at an 10H116 (U502) and this last one at the alien ic U501.

  6. Richard Klingler

    According the the compatibility matrix the 16533A and 34A cards won’t work in a 16500B….or are there different CPU boards versions for the 16500B?

    1. martinjonestechnology Post author

      I’ve got three 16534A cards, all working now since I wrote this article. Two of them are relatively new – at least one is labelled ‘Agilent’ rather than HP. The new newish ones both have labels on saying ‘not suitable for 16500B mainframe’ or something similar. However, they all work fine in my 16500B mainframes, with one exception: the ‘logic trigger’ function won’t pass in calibration mode. All other self tests and calibrations pass fine. I haven’t tried the advanced logic triggering modes in practice, but the scope modules are perfectly usable as they are. There may be some more subtle incompatibility but I haven’t found it yet.

      I’m not sure about the CPU board versions of my mainframes, however. I haven’t checked them though I could have a look at the motherboard software revision at startup.


      1. Richard Klingler

        Hello Chris

        Thanks for the quick answer (o;
        So you’re saying all 16534A have this triggering problem?

        Maybe I find some cheapo 16534A cards on ebay to have a go at it as well (o;
        Or you can spare one for an educational price (o;

        Just started going into the logic analyzer field and start enjoying it…

        Currently I do a write up on a 16500A to 16500B upgrade with a new CPU board over at eevblog:


        And about a second 16500B I received with failed ROM test…so now the ROM images are also available for the 16500B CPU board (o;



      2. martinjonestechnology Post author

        I don’t think they all have this triggering problem. I found that the fault in mine was in the interpolator, which does actually use the AD96687 chip but not in the way I thought. Putting my fingers on that area would make it pass the test sometimes! It was behaving as if some signal was missing. I added a bias resistor to pull the offending line into a range that worked, and now the card basically runs but has up to 10ns trigger jitter, which is good enough for me. I made some notes on what I found and did which one day I’ll write it up.

  7. Spork Schivago

    Hey Chris,

    I stumbled across your website when I was looking for schematics for my HP 16534A module. I just got it in the mail today. The seller said he couldn’t get triggering working. I haven’t received my HP 16702B Logic Analyzer mainframe yet but figured I’d give the board a once over. I found some components on the back side that appear to be missing. One looks like it has a pad broken off.

    If I sent you a link to pictures of my board and the “missing” components, do you think you could check your boards to see if they have anything in that area? I’d greatly appreciate it. Just finding out if something goes there could be a big help. Figuring out what value component though, that’s gonna be another story! Thanks!

    1. martinjonestechnology Post author

      Sure, no problem. Next time I get a board out into the open (mine are all in chassis at the moment) I’ll have a look. You probably won’t have to wait long because the 16534A at work is giving trouble (a RAM fault) and I need to swap it with one from home.

  8. Ken Swarthout

    Hey Chris,

    I have a HP 16534A that has a broken trigger as well. However, I think my problem is a bit different than yours. There’s a heatsink near the front that says U509. On the underside of the board, at that location, there’s some components. Two of those components appear to be missing from my board. I was hoping maybe you could take a close up picture of the back board, right at that location, so I could see what those two components are and maybe try finding replacements. You’d really be helping me out alot! I can’t seem to find schematics anywhere for this board! Thanks and awesome work on getting those working!!!

      1. Ken Swarthout

        Thanks! I ended up finding someone over at EEVBlogs to give me the info I needed. I believe I’m looking for 10nF SMD caps. Just not sure what type of SMD cap and what voltage rating I need…

  9. filippo

    Hi guys.
    I just fixed one 16533 with broken triggering.
    Failed ADC and TRIGGER AND IMB….
    It was working OK a week ago and I calibrated it successfully.
    Suddenly I was playing with external triggering and combined triggering from another 16533… and it died, refusing to trigger, only auto triggering when pressing stop.

    The problem….

    corrosion under the two plastic sort of skids.

    I will write up something at EEVBlogs and put some pictures there.


    1. martinjonestechnology Post author

      Yes, all of my 16534As have this corrosion problem. Removing the skids and the adhesive and then finding the broken traces and fixing them with mod wire can fix all sorts of faults.

  10. filippo

    could you post detailed images of the 16534a
    I am trying to understand the difference with the 16533a
    Maybe the 16533a can be modified?

  11. martinjonestechnology Post author

    I do have an image of the 16534A – where can I send it to you? Looking at it, the PCB has ‘16534A’ etched in copper traces, so it’s probably not the same board as a 16533A. Modification of one to the other would be interesting!


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