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probes for tektronix 7904 analogue scope

Discussion in 'Electronic Design' started by Sam Kaan, Jan 17, 2004.

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  1. Sam Kaan

    Sam Kaan Guest

    I am astounded by the number of oscilloscope probes out there and how
    getting the wrong one would be useless for your scope.

    I have a 7904 oscilloscope and wanted to get one that will work with
    it.
    I just realize the one I just bought (Probe Master) is broken. A
    continuity
    test from the BNC end to the other (probe tip) failed!

    So now I am going to try and get one that will work, but also the
    correct one.

    I am thinking of the Tektronix P6139A probe which is rated up to
    500Mhz.
    However I am not certain if this will work on a Tek 7904 machine. The
    person selling says he only knows that it works for Tek TDS series
    machines, which are digital oscilloscope.

    Can someone please give a bit of insight into this? First of all
    would the P6139A work in a 7904 frame? What is the difference between
    digital and analogue probes?
     
  2. I read in sci.electronics.design that Sam Kaan <>
    If it's a 10:1 probe, it has a 9 megohm resistor in there! Your meter
    may well not show that.
     
  3. See
    http://www.tek.com/Measurement/App_Notes/ABCsProbes/60W_6053_7.pdf

    Cheers
    Stefan
     
  4. mike

    mike Guest

    Your 7904 doesn't care what probe you use. It's the vertical plug-in
    that you have to match. And you haven't said what that is.
    Most are 1Meg inputs, but you have to have enough range on the probe LF
    compensateion tweek to match the input C of your plugin. Check the
    compensation range spec of the probe against the input C of your plug-in.

    Some plugins are 50 Ohm input and require an eitirely different probe.
    Then there's that whole bit about high frequency compensation/accuracy/
    transient response, etc. Low quality probes, even when properly
    compensated at LF, can seriously degrade the high frequency performance
    of the system.

    What's your definition of continuity? If it's zero ohms, vritually all
    pobes will fail. Even a properly constructed 1X probe can measure
    several hundered ohms from tip to center conductor of the BNC.
    10X can measure 10 meg from tip to ground, 1meg or so from bnc center to
    ground and 9meg from BNC to center conductor at connector. And they
    make 100X probes that can be higher.

    So, disclose the plugin you have and the exact model probe you already have.

    Also, the 7000 series has a bewildering (to the uninitiated) array of
    buttons and controls that all have to be set right to make things work.
    I assume you have proper operation at the plug-in BNC and are SURE your
    problem is in the probe.
    mike

    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S $800 in PDX
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  5. Sam Kaan

    Sam Kaan Guest

    Well, I have a 7A13 plugin on the left vertical, and a 7B52 on the right
    horizontal slot. Scope is Tektronix 7904.
    The probe is a "Probe Master model 4906-1RA" 10x 300Mhz
     
  6. mike

    mike Guest

    Ok, without looking up the compensation range of the probe, you should
    be able to get something thru it. The 7a13 has 20pF Cin. Although
    I didn't find the exact numbers I wanted on their website, a little
    cross referencing indicates that the probe you have is probably just fine
    for the 7A13.

    First things first. Are you set up so you get a green/blue line near the
    middle of the screen with nothing connected to the vertical input?
    When you stick the signal directly into the BNC
    of the 7A13, do you see the signal on the scope? When you try with the
    probe, do you increase the scope gain by 10X to account for the 10X
    reduction in the probe? The probe does not change the gain of the
    plugin, it merely changes the readout to reflect the reduced system gain.
    mike

    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S $800 in PDX
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  7. Sam Kaan

    Sam Kaan Guest

    Yes I can see a green line across, which I positioned right in the middle
    of the
    screen.
    Nope, green line not moving at all. By the way there are two BNC on the
    7A13
    one is marked -ve and the other is +ve. I have tried both, and green line
    not
    moving.
    Green line not moving even with using the probe. I suspect this 7A13 is
    toasted.
    I am currently ordering a 7A26 which should be coming within a months time.
     
  8. mike

    mike Guest

    If you can position the trace with the vertical position control, at
    least some
    of the plugin is working. Push the AC button on the + input.
    Push the ground button on the - input. Stick the signal into the +
    input. Make sure your volts/division is in the correct range for
    the signal you're putting in.

    What are you using for your test signal?

    Are you sure your signal source is working? Switch the + input to
    DC and try a battery.

    Forget the probe until you get something in the BNC.
    mike




    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S $800 in PDX
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  9. Sam Kaan

    Sam Kaan Guest


    Well, for test signal I have a AC-AC transformer (120VAC to 16VAC nominal).
    I think this transformer is
    working because I hook my digital voltmeter up to the 16VAC side and it
    reads a voltage, although 40VAC
    is shown instead of 16VAC nominal.

    Anyway, I just tried hooking up a battery to it and trace just didn't move.
    I pushed the DC button on the +input then Ground on the -input.
    However I am not sure if I am hooking the battery output correctly to the
    pluggin. What I did is push the positive lead from the battery
    into the plugin's BNC little hole in the middle. And push the negative lead
    from the battery onto the outer shell of the pluggin's BNC connector.
    Sounds about right?

    Note the at the base of the plugin BNC connector is a ring that is separated
    from the BNC connector. I guess this is for the little pin on the probe
    to touch for readout or something.
     
  10. mike

    mike Guest

    Sounds like your plugin is bad. There are some strange channel switch
    issues. Make sure the mainframe vertical selector is set to the correct
    hole, but I think, if the vertical position knob works, you should
    be good to go.
    mike

    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S $800 in PDX
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  11. Jim Yanik

    Jim Yanik Guest

    7A13 is only a 100Mhz plug-in,with a 1 Megohm input Z.
     
  12. Jim Yanik

    Jim Yanik Guest

    7A13 input FETs(matched pair) are vulnerable,easy to zap,and the little
    white relays fail often,too.There are several of those relays in the 7A13.
    IIRC,4 in the attenuator,a pair for input switching,and a couple more for
    gain switching on the main board.
     
  13. Jim Yanik

    Jim Yanik Guest

    The 7A13 is a good,useful PI,but the 7A26 is an even better choice for the
    beginner.7A26 is also a 200Mhz bandwidth in the 7904,and has a useful 20Mhz
    BW limit switch,cuts displayed noise when you don't need the higher BW.
     
  14. Sam Kaan

    Sam Kaan Guest

    Maybe that's one reason it didn't work. A 300Mhz probe on a
    plugin with just 100Mhz bandwidth
     
  15. mike

    mike Guest

    No, it's not.
    mike

    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S $800 in PDX
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  16. You must be doing something wrong - a 16 volt transformer should not
    measure 40 volts. (Although, if the secondary is center-tapped, and
    marked 16-0-16, you would get 32 volts across the full secondary,
    possibly 36 volts or so with no load)

    It is also possible the battery in your DVM is dead - someone else
    recently was getting higher-than-expected voltage readings due to a
    dying battery in his DVM.
    If I remember correctly (I'm not near my 7904 at present), the 7904
    has a probe calibration output on a BNC connector - I think that gives
    a 1 volt, 1 KHz square wave - connect the calibrator output to the
    vertical amp input (it would be best to use a BNC cable, but hookup
    wire between the center conductors of the BNC connectors will work),
    and you should see a square wave on the screen. Set the vertical amp
    to 0.5 volts/div, and the time base to 0.5 mS/div, and the trace
    should be two divisions high.
    Yes - if you ground that outer ring, the scope will think a 10:1 probe
    is attached, and will change the on-screen volts/div readout
    accordingly.
    --
    Peter Bennett, VE7CEI
    peterbb (at) interchange.ubc.ca
    new newsgroup users info : http://vancouver-webpages.com/nnq
    GPS and NMEA info: http://vancouver-webpages.com/peter
    Vancouver Power Squadron: http://vancouver.powersquadron.ca
     
  17. Jim Yanik

    Jim Yanik Guest

    No,the 300Mhz scope probe merely has a better quality compensation network.
    So it has a better rise time and less ringing than a 100Mhz probe,distorts
    the input signal a bit less at the higher BW.
     
  18. Jim Yanik

    Jim Yanik Guest

    IIRC,it's 40mv,400mv,4v,and the freq can be switched from ~1Khz to DC,or
    the sweep gate signal of the timebase being used.(or OFF)
     
  19. Seriously bitchen fast CRO. Way to go! Having said that your selection
    of plugins are letting you down, if you plan to use the speed of this
    raw analogue power house. A 7A26 will take out to 200/250 Mhz depending
    when made with a 1M probe, a 7A24 to 400 Mhz (Dual trace) 50ohm or a
    7A19 to 5/600 Mhz (50 ohm)and a 7A29 to 1 Ghz (50 ohm) (that is flat
    response) Tek V.A. usually had a single pole role off response, so you
    still have sensitivity way past the spec. I use a 7B15 Time base ,1Ghz
    but a 7B85 or 95 or 10 is an equally fast T.B.

    As for probes a good F.E.T. probe is the go for RF measurement. These
    are available from HP and Tek for astronomical figures, but there are
    one or two available from the taiwanese at more reasonable figures.

    If you are just using it for service or as a cheapy (God forbid) then
    any Dick Smith cheapy (like Hosdein?) will do.

    regards Andrew
     
  20. Jim Yanik

    Jim Yanik Guest

    No,a 7A29 will not make a 500 Mhz mainframe go to 1 Ghz.
    7A29 will only give 1 Ghz in a 7104 (1 Ghz)mainframe.
     
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