troubleshooting Tektronix 454 scope

Discussion in 'The Projects Forum' started by tonydix, Jul 2, 2014.

  1. tonydix

    Thread Starter New Member

    May 4, 2010
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    OK until today was working perfectly. Now today no sweep at all.
    After warm up two spots can be seen. These spots can be centered both horizontally and vertically. But on every position of the time/division control does not move the trace across the screen. Also I am suspicious that some thing might be wrong in the Y circuits. Putting a 9 volt battery across the CH1 probes does not move the spot vertically. Checked the important voltages and all seem within spec.
    Help with further troubleshooting would be appreciated.
    Tony
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Do you mean a Tektronix 524 oscilloscope?
     
  3. tonydix

    Thread Starter New Member

    May 4, 2010
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    Sorry it is a 454 oscilloscope
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    I had one back in the 90s. Good scope. You can down load the service manual off of the net for free.

    What other test equipment do you have to work with?

    Mark
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Possible blown fuse (or fusible resistor) feeding power to the H deflection circuitry. Gives total loss of H deflection, and can happen overnight.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    manual before you go jumping inside, just check the controls on the front that the are in the correct setting for normal operation.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    first get a manual, then check all the power supplies. power supplies have more of a chance of failure than anything else, due to being the parts closest to the outside world, lightning, surges and such.
     
  8. bance

    Member

    Aug 11, 2012
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    Here is a guide to help you...

    HTH Steve
     
  9. tonydix

    Thread Starter New Member

    May 4, 2010
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    Still trying with this beast ! The display has been 2 spots that can be moved both vertically and horizontally. But if the mode is set to chop a lopsided rectangle like a paralleogram with curved corners appears.
    In other modes the beam finder will find the spot but centreing it and releasing does not show any image
    The intensity control seems to ineffective but the focus seems to work.
    I wonder if this gives any more clues.Thanks for any advice
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If the dot can be moved H and V with the correct controls, then the deflection amps are working properly.

    Your symptom then becomes that the input signal is not getting to the V deflection amp, and the H scan sawtooth wave is not getting to the H deflection amp.

    And you have another symptom of the intensity control not working.

    I still think you are dealing with the loss of a PSU rail (re my earlier post). This is likely to be a preamp PSU rail, used for signal preamp and H sawtooth osc (and/or H preamp).

    It should be an easy enough thing to track down, now people have given you the manual and other tech info.
     
  11. tonydix

    Thread Starter New Member

    May 4, 2010
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    Thanks for all this help. All the power rails seem OK I have followed the calibration instructions for the -12v. +12v, +75v and EHT supplies. All seemed adjustable to the desired voltages I have the manual and it has a troubleshooting section and I have followed it as appropriate :-
    check for sawtooth at pin L of A sweep board ----Seems ok
    check for sawtooth at deflection plates ----------- seems ok
    check A unblanking gate at TP 715 on A sweep board --- well not quite sure what to look for but there is activity that looks OK.
    Check unblanking gate at TP 1349 of Z axis board ??
    I can find TP 1349 but what does this mean how do I decide either yes or no ?
    Again many thanks
    Tony
     
  12. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Could you post a photo, or even better, a video of the issue? I'm having difficulty picturing it.
     
  13. tonydix

    Thread Starter New Member

    May 4, 2010
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    I have made a video but no sound track plays when I try to insert it into a reply here. The video is showing a ch1 spot moving left right up and down and the same for ch2. In both cases no sweep appears whatever postion of the time control.
    Moving the displayed channel to chop creates the funny rectangle with slightly rounded display you see on the screen Any help much appreciated. Tony

    [​IMG]
     
  14. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You don't have it set to A vs. B mode, do you?
     
  15. tonydix

    Thread Starter New Member

    May 4, 2010
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    I dont think so.

    What is interesting is I do get a single sweep as follows :-

    Get a single sweep for all times fast through slow when :-
    A sweep mode is moved to single sweep, B sweep mode is in either position, Atrigering can be DC or HFrej or LFrej but not AC.

    Does this suggest a problem with the A sweep mode switch or its associated circuits.

    Tony
     
  16. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Hmm, interesting.

    Out of curiosity, have you opened it up yet? Curious to see if there's any visible damage to the PCBs. That's usually the next thing I do after making sure it's not just a control issue.
     
  17. tonydix

    Thread Starter New Member

    May 4, 2010
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    Yes all opened up and probing around with the only other scope I have which is a pc based hantek scope. The boards all look good no visible sign of damage. The schematic has some sample traces and I will keep probing, but I am a bit intimidated by all these feedback circuits. Thanks
    Tony
     
  18. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Woops, missed the part of the thread where you said you were probing it. My mistake :p

    Could you take some photos of inside the scope? I haven't repaired any of this model before, so I'm curious to see what's inside.

    Thanks,
    Matt
     
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