Tektronix Problems Need Help

Discussion in 'General Electronics Chat' started by juarboleda, May 2, 2014.

  1. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Hi, all, I bought an analog Tektronix 2336 YA scope off of vendor a few days back. Almost everything appears to be fine with it (i.e. horizontal beam, visible CAL square wave, etc.) as far as I can tell, as this is my first scope. However, when I try adjust the beam vertically on the screen, I can only get it to go about halfway up the screen. Similarly, when I adjust it down past the bottom of the screen, the beam becomes scrambled near the top of the screen. No full Screen only 4 Division (2 Top and 2 Down) ( if I need DC voltage in 1 Volt Division buttom, only show in subdivisions (per Volts) 5 Volts in One Division)
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Do you have a function generator or some way of inputting a signal?
    Even a 50/60Hz sine wave from an AC transformer or wall adapter will do.
    Adjust the VOLTS/DIV setting to expand the trace vertically.
    Is the trace amplified correctly or is it compressed at the top and bottom?
     
    Last edited: May 2, 2014
  3. gootee

    Senior Member

    Apr 24, 2007
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    Is it the same for both channels?
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Vertical amp fail.

    Possibly one PSU rail has failed, going to the push/pull vertical amp. Or one of the push/pull drivers.
     
  5. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Yep compressed at the top and bottom in Two Channels
     
  6. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Thanks for answer, yes Both Channels
     
  7. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Thanks for answer, Sorry what is PSU Rail ?
    Thnks again
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Moving forward, you will need the schematics and a voltmeter for testing.

    What RB is referring to by PSU is the Power Supply Unit.

    The first thing you want to check is the +ve and -ve power supply voltages (rails).
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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  10. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Thanks for help, short video about the problem https://www.youtube.com/watch?v=K62D2QTjU5M
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Vertical amp caps. Do you have a capacitor ESR meter?

    Or can you show photos of the vert amp PCB?
     
  12. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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  13. THE_RB

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    Thanks for the photos. :)

    Is that the vertical power amp? Looks more like a preamp? Normally for the vert amp there are some power transistors (or a chip) on the heatsink. Maybe they are under the PCB?

    Another easy way to find the vertical amp is to trace the wires back from the vert deflection yoke.
     
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  14. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Yes Under PCB as U54 Ver Output Amplifier atach diagram and photo Thanks again

    [​IMG]

    [​IMG]
     
  15. THE_RB

    AAC Fanatic!

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    Ahh, thanks for that.

    I don't have much to offer you at this point from viewing the photos. There doesn't seem to be many electros there, and there does not seem to be much corrosion.

    Basically at this point you need a 'scope (!) and start tracing a sinewave from the input amp through to the vert preamp and amp.

    That's assuming you have checked all the PSU rails for the correct voltage and ripple, which should be easy since you seem to have the service manual now. And it's always worth checking all the knobs/switches/connectors for corrosion (work then back and forth etc).

    At this point if the PSU rails are all OK my money is on the 20pin preamp IC or the main vert amp IC. Sorry. :(
     
  16. Redcatimaging

    New Member

    May 8, 2014
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    Hi Juan,
    thanks for answering on the video comment.
    I have found the way to your tread ;).
    As I said, I think the problem is in the vertical output stage, and as I see other have said too.
    Some questions are unanswered. Could you please try to answer these?

    -If you switch to GND, can you move the trace to the top?

    -Is the amplitude of your signal the right value as it's showed (for example, your signal amplitude is 1.5V - AA Battery the easiest - and when you switch to 500mV/div you get 3 divisions jump up)?

    -Are the Voltages really ok?
    Please measure the Voltages around U43 with the help of the Vertical Output Amplifier Schematic on page 224 (and before) of the manual pdf.
    Have you +40 and +10 V at U54? (look at the schematic).
    What Voltage do you have on TP (testpoint) 25,26,27,28,27+28 ? Are they ok?
    I expect somewhere is a voltage not ok and we can try to start searching from this point.

    Yes, it would be the best if you had another scope, but I read you don't , so will not be easy.

    Does anything get better (more than 6 div) if you set your signal (can use the probe comp signal) to the max 6 divisions and play a little bit with R44 (vertical gain)?

    Will try to follow the tread ;), good luck, Tom
     
  17. juarboleda

    Thread Starter New Member

    Apr 25, 2014
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    Replace the
    TEKTRONIX Part No.155-0218-00 from ebay and work again



    Juan
     
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