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Probes for Nicolet 3091 scope?

Discussion in 'Electronic Equipment' started by Lewin A.R.W. Edwards, Sep 25, 2004.

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  1. I recently acquired a Nicolet 3091 digital storage scope, vintage
    circa 1982. The manual is amusing; for instance, it says that the
    device has 16x12 of RAM, and a single screenful is 4096 12-bit words -
    it is possible to dump out an entire screenful on the RS232 interface,
    but "due to memory limitations of personal computers, you will
    probably not want to acquire the entire image".

    It's an audio-bandwidth scope (speced 300kHz BW, up to 1MS/s). I have
    a much better digital scope, but this freebie has RS232 built in, and
    it also has a couple of useful features like a "virtual pen-recorder"
    mode. I want to use it for unattended analysis of battery chargers.

    Anyway, I'm having trouble finding a probe that will match this scope
    properly. Here's what the calibrator output looks like:
    <>. That's the best I can adjust it
    to using the trimcap on the probes available to me (mostly x1/x10
    switchable units of post-1998 vintage at oldest). If I just hook a
    piece of wire to the cal output, the trace looks nice and square. So
    it's a probe capacitance issue.

    What characteristics should I look for in a probe for such an ancient
  2. Steve

    Steve Guest

    I worked for Nicolet as a final test tech about 20 years ago, and of
    course we just shipped the probes we were given not realizing they were anything out
    of the ordinary. Unfortunately, my service manual for the 3091 either doesn't
    seem to want to be found. They are available via the web. The only genuine
    Nic' scope probe I have has no adjustment apparent to me on the probe itself.
    (?? and !) That would seem to suggest an internal adjustment -- I recall a
    cylindrical pf range trimmer that needed adjustment, with a brass screw.
    One hint, from the 1x scope probe I have here, is that it does have a 33 Ohm
    resistor in series with the probe cable, located at the BNC. So perhaps
    they are more special than I ever realized or at least remember. The 4094
    that I own works fine with plain old scope probes of "today."

    Given your present slow application, you should be fine for
    your immediate need with nearly any probe.

    Don't know if this really helps much. I'll try to rattle a few
    cob webs in my mind and ask a few old contacts to see what I can find yet.
    My 4094 needs several new Grigsby switches, but so do they all; I doubt
    I can find what I need myself.

    Thanks, Steve
  3. Hi Steve,
    Heh, heh. Well, maybe you handled this one. It was last cal'd in
    December 1983 and it was signed off by one Douglas M. Abner. In actual
    point of fact, it was probably never cal'd after manufacture, because it
    was used for engineering tests - at my company, equipment that isn't
    used for actual final Q/A or other important things (e.g. UL or FCC cert
    work) is tagged "CALIBRATION NOT REQUIRED".

    We've got vast graveyards of equipment that are slowly being tagged for
    disposal. A true friend, gentleman and potential saint in the
    "graveyard" building occasionally drops by my cube (I work in a
    different building) and says "There's a [xyz] about to go in the
    trash..." I'm hoping for another one of these 3091s, rumored to be in
    the same general area of the junkpile, to use as spare parts if
    necessary. I was shocked to see that a unit on eBay was going with a
    starting bid of $200-and-something. It didn't sell, of course.
    I've got the original letter-size printed service manual, as well as the
    half-letter-size user manual. There isn't any information in the service
    manual on what's inside the probes or how to calibrate them.
    Well yes, that's true, but I would like to get the instrument working as
    nominally as possible. I'm contemplating hacking up a probe myself, by
    modifying an existing probe. Since it appears to get a good waveform if
    I use a dumb wire, maybe I should take a "new" probe, pull out any
    smarts inside it, and add that 33R resistor. Thanks for the pointer!
    Grigsby switches - what are those? I found the only thing wrong with
    this old beastie was (a) tube rather out of focus (I can compensate
    slightly with the focus adjustment, but not much - I'm guessing a cap
    job is called for at this point in time), and (b) all the rotary
    switches desperately needed cleaning.
  4. Tom Woodrow

    Tom Woodrow Guest


    Did you ever work with a John Holton while you were at Nicolet?

    Tom Woodrow
  5. Steve

    Steve Guest

    I don't remember him. Actually I showed up in '85 to '86.
    My working 4094 I bought for $5.00. A non-working one I got for $15.00!
    They sold originally sold for 1000 to near 10,000 times that new if you
    bought a lot of bells and whistles!
    I did just find a box O' junk, with a 3091 ADC board in it, and there is
    no such piston cap on it. There are two pairs of 3 to 10 pf trimmers. Please
    just forget what I said about the internal adjustment... I even
    wonder if this Nicolet scope probe was for a 3091. The years cloud the memory.
    The rotary switches are made by Grigsby. They are the major source of
    demise for many a Nicolet scope. Cleaning only delays the inevitable.
    As I only got the two 4094's in the past year, I don't really have
    much experience about the "end of life" of these scopes! Very unsure
    about how much luck one would have ripping one apart to clean
    it, or if possible at all. At the factory we would have never done
    anything but put a new one in for the occasional infant failure during
    final test.

    Good luck, and I'll try to see if I can come up with anymore help.
    May take weeks.

    Thanks, Steve
  6. Steve

    Steve Guest

    Sorry, he looks to be before my time there, from what I could Google about
    him, if this is him:

    Looks like he may have been in the Bio-medical division.
    Of course I was in the O-scope division. There were hundreds working there,
    in 1/2 dozen buildings. Not anything close to what's left, from what I've
  7. Tom Woodrow

    Tom Woodrow Guest

    Don't think that this was the same guy although the time frame is about
    right. The John Holton I knew was a vietnam vet and still had long hair
    and beard so I can't tell from the picture.

    On another note, when I was at Aydin we had a 4094. Was a great DSO and
    was the world's best glitch catcher. We did high voltage stuff and just
    the ground faults would kill a Tec scope. We never did fry a 4094. I
    coud still use one once in a while, but the last one we bought (another
    company) disappeared after a move to a new building.

    Tom Woodrow
  8. My working 4094 I bought for $5.00. A non-working one I got for $15.00!
    I'm thinking of offering that eBay seller $50 + shipping for his 3091
    (he claims it has bubble, but it doesn't have that option fitted) as a
    parts unit. It really is very (surprisingly) useful to have a DSO that
    can go down to such slow sample rates.
    Mine work, but when you change the settings you need to massage a little
    to make sure the setting isn't twitchy. I want to try blind-squirting
    contact cleaner into them and working them vigorously, then blowing
    compressed air through to get rid of any loosened debris. But I want to
    be sure I have a donor unit for spares first ;)
    Hey, thanks. Would you mind emailing me if you do find something? If
    it's just a random message drifting by in this NG I may well not see it.
  9. Jim Adney

    Jim Adney Guest

    The scope will have an input resistance and capacitance. On Tek scopes
    this is marked on the front panel. What does the NIC scope say?
    You need to use a probe which has a compensation range that includes
    the input capacitance of your scope.

  10. Jim Adney wrote:

    It's not characterized on the front panel. I think it's probably in the
    range ~150pF, at a guess, and my probes are designed for ~13-15pF input
    capacitance. I'll look closer at the instructions (they are filed now..
    didn't think I would be needing them immediately).

    At the moment the scope is running a ten-day data acquisition operation,
    I'll play when that's over (it has an ultra-low sample rate, down to 1
    sample per 200 seconds, and a 4096-point memory).
  11. TekMan

    TekMan Guest

    The probe you use does not satisfy the scope'S input capacitance with
    it's (the probes trimmer) compensation range.

    That is NOT unusual: The 3091 has a quite high (compared to nowadays)
    scopes capcitance (AFAIK 1Mohm par. 47 or 60pF). Only a few probes you
    can buy nowadays can satisfy that input.
    check the probes data, or go for an older probe (e.g. Tektronix has
    some probes for the "legacy" scopes from the 70's to satify the
    range). I don'T know the product number by heart, but you can look it
    up in the Tektronix catalogue together with the probe data.

  12. Jim Adney

    Jim Adney Guest

    I doubt if it's as high as 150 pF. I believe the highest input C that
    Tek ever used was 40 or 45 pF.

  13. I say this number because googling around I've found a couple of people
    using it with probes that are speced at "147pF". Oh well. In a few days
    I'll be able to play again...
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