The Problem of HP 16500 Logic Analyzer.

Discussion in 'Test & Measurement Forum' started by v40163, Jun 13, 2018.

  1. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Good afternoon all,

    I have no real hope of anyone being able to help me but this is my last hope.

    I have an HP 16500 logic analyzer. It will start and run for anywhere from a couple of seconds up to say a minute, to the point where it will have completed its boot process and is waiting to be used normally.

    However, at that point it will shut down and attempt to come back up, fail, and then try again. It is clear that the power supply is the thing that is shutting down and then once it has shut down is trying to come back up, over and over again.

    The system architecture is typical 90s--

    There is a backplane into which are plugged:

    1) The CPU card

    2) The power supply card

    3) The various logic analyzer cards—I have four: two 1 GSPS cards, and two 100MSPS cards

    4) Power to two fans

    5) A front panel interface connector (ribbon cable/IDE connector)


    The video monitor assembly appears to be a separate assembly that was manufactured by Sony. There are a couple of cables that leave the video monitor assembly. One cable goes to the front panel and the other to a five pin connector on the power supply card. I assume that the second one is power to the assembly.

    Okay, that’s the setup. I have done the following:

    1) I removed the four logic analyzer cards

    2) I disconnected the power to the two fans

    3) I disconnected the front panel interface ribbon connector

    4) I disconnected the various video monitor cables


    With the four items above removed/disconnected the unit still tries and fails repeatedly to start.

    I removed the CPU assembly from the backplane. After I did that the power supply refused to run at all. I therefore assume there is some kind of “CPU Installed” signal that the power supply needs in order to run. After I reinstalled the CPU the power supply “hunting” continued as before.

    The unit has worked until recently and as I said at the beginning does come up and run for a short time, sometimes for as long as a couple of minutes before falling back into the "start-stop-repeat" sequence.

    The Power supply card:

    1) The power supply card runs on 115vac (the cord actually plugs into the back of it) and there is an LED on the board that indicates that 115vac is present when the power switch is ON.

    2) There is an LED on the board that indicates when 120vDC (yes, DC) is present. There don’t seem to be any bleeder resistors across the large capacitors in the power supply so even after the power is turned off and the power cable disconnected both of those LEDs are illuminated for some time and to some degree, indicating the presence of charge on the capacitors. In fact the HP 16500 service manual points out explicitly that the service person is to wait at least six minutes for the charge to bleed away.

    3) The service manual has a table of voltages that should be present on the power supply backplane connector. During the time that the unit is running properly the voltages are present. However, when the power supply is “hunting” the voltages rise and fall as you might expect.

    I mentioned the possible lack of bleeder resistors above in order to make the point that in my experience here the chance of the unit starting properly (and actually running for a couple of minutes) increases dramatically the longer the unit is off between my attempts to get the unit to turn on. So maybe there is a voltage monitor circuit somewhere that is supposed to hold off startup until one of the voltages reaches some level--and maybe it’s out of whack, I don’t know.

    I think this would be pretty easy to troubleshoot if I had the power supply and/or CPU board schematics. However, HP/Agilent no longer sell or support this unit and the service manual has no schematics or wiring diagrams.

    I’m interested in any suggestions. And of course I am hugely interested in getting a schematic of the CPU and/or the power supply card.

    Thanks in advance,

    Ray Russell

    Houston, TX

    A bit of irrelevant history: Back in the 90s I bought a 16500B for the company for which I worked as a design engineer on DOD programs. It was an incredibly useful piece of equipment for debugging designs. If I recall correctly they were running about $20k at the time. Functional units today seem to be readily available on eBay for under $150 with shipping. I would say that is the deal of the century if you can find one that works—and that seems to be pretty easy to do. Who knows, I may just say to hell with this one and buy another one. That just offends my sense of DIY--ness.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    17,123
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    What does that say about how much confidence you have in abilities of the members at AAC?

    Welcome to AAC!
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    What is the model and serial numbers?
    Can you show us some photos of the front and back panels and a view on the inside?
     
  4. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Lol, I certainly didn't mean it THAT way!!! What I was implying was that the unit is 25 years old and i don't hold out much hope of anyone seeing my post and going, "Oh wait a sec, I have those schematics out in the garage!"

    Nothing more than that...

    Apologies if I ruffled anyone's feathers. i meant no offense...
     
  5. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Of course:
    Manufacturer: HP, prior to being Agilent
    Model number: 16500B
    Serial number: 3206A08557

    Pictures will follow in a few minutes.
    Thank you for taking the time to reply. I mean that.
     
  6. dl324

    AAC Fanatic!

    Mar 30, 2015
    7,240
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    Are you looking for a service manual? I have one.

    I picked one of these up for about $30 about a decade ago. The last time I fired it up, it work; but it's so bulky and noisy that I choose to use other equipment. I have several 16 channel logic analyzers and I didn't find the 2 channel scope very convenient to use. The only problem with mine is that one of the floppies doesn't work, so making copies of the disks is problematic.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    No offense, really.
    You could be pleasantly surprised with the resourcefulness of our members on AAC.
    Someone will come along with a manual and trouble shooting advice.

    Edit: I told you so.
     
  8. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Okay, I think I have uploaded pics of the front, rear, inside, and a fourth shot which is just one of the data acq cards.

    And thank you Dennis but I do have the user and service manuals.

    And I just found that Keysight Technologies which among other things appears to sell and service test equipment may have been the OEM for some of the boards that are used in the unit. So maybe THEY are my last hope! Lol

    Anyway, we'll see whether the pics arrive.
     
  9. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Yes, the two fans inside certainly make it fairly loud. But I spent so many years around jet engines that the noise doesn't bother me for some reason. Lol

    There are cards for sale around the internet, and especially on eBay. But the cards seem to be as expensive as buying an entire functioning unit.
     
  10. dl324

    AAC Fanatic!

    Mar 30, 2015
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    I was lucky. The unit I bought was listed on eBay by a recycler that had a facility 30 miles from where I live and they offered local pickup. A couple people bid on it, but the shipping cost was prohibitive. So I got it for around $30, some gas, and a couple hours of my time. Luckily mine came with all of the logic analyzer probes and grabbers.

    My 16 channel logic analyzers are Tektronix 7D01. I picked up my first one for about $50, but it didn't come with the probes. I paid $200 for a set because it was useless without them.
     
  11. v40163

    Thread Starter New Member

    Jun 13, 2018
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    I just looked up the 7D01. Looks like it was out around the middle 70s. I think back then I was just using multiple scope probes! Things were simple back then...
     
  12. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Some cropped pictures of the two important ones:
    upload_2018-6-13_20-49-7.JPG

    upload_2018-6-13_20-34-5.JPG
    EDIT: reduced image file sizes
     
    Last edited: Jun 13, 2018
  13. dl324

    AAC Fanatic!

    Mar 30, 2015
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    I was learning electronics in the 70's and our school lab had a lot of Tek equipment, so I developed a preference for Tek.
     
  14. v40163

    Thread Starter New Member

    Jun 13, 2018
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    I started my career in late 1972. Virtually all of the scopes that I ever used were Tektronix, starting with the 541. Google a picture of it for a good laugh! Even though I had access to DSOs for the last half of my career I still preferred using good old 2465Bs. In fact, I bought a couple from eBay after I retired. I think one of them may be in one of the pics that I uploaded last night.

    I never got used to HP scopes although HP was the brand of choice for most other things I used--spectrum and network analyzers, power supplies, etc.

    Oh, and the first Z80 development system that I ever used was a Tek unit. Can't remember the model number but I do remember that it used 8 -inch floppies...
     
  15. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Update on the problem for anyone who might come after me:

    I contacted Kesight who apparently was a repair depot for the 16500 back in the 90s and may in fact have actually manufactured some of the boards.

    They replied this morning, saying that the unit had been discontinued 20 years ago and had not been supported for 16 years (I knew that). I was disappointed to find that schematics are not available.

    So I guess that's that, unless someone has a set laying around in their garage or something...
     
  16. v40163

    Thread Starter New Member

    Jun 13, 2018
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    Another update: Keysight Technologies is a spin-off from Agilent, which of course was spun off from HP. So they were not JUST a repair depot-they were the actual manufacturer. So if the schematics aren't available from them then I have little hope of finding them.

    In other news, I actually RTFM (Read The ... Manual). It gives the Motorola uP part number and references a voltage supervisor circuit (my original thought as to the culprit), as well as how the VS asserts the uP "HALT" and "RESET" signals. I'm going to start there and see where that leads me.
     
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