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Tektronix 2235 reduced horizontal sweep

Discussion in 'Troubleshooting and Repair' started by erdrd, Nov 20, 2016.

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  1. erdrd

    erdrd

    1
    0
    Nov 20, 2016
    The scope was working great... then I moved.

    When turned it on after unpacking I noticed that sweep only showed only in the left side of the display. Could move it a bit towards the right (to the 1st major division to right of center) with the Position adjustment, at which point the waveform got a bit compressed. I could also move it off screen to the left for a couple of major divisions.

    I then opened the scope up (I have a scanned service manual) and adjusted the Geometry (R870) to center the waveform. With a 1 kHz sine input at , I get a maximum display width about 1.5 major divisions off the center to each side. I can move the display fine left and right with the Position adjustment.

    I then tried adjusting the A GAIN (R740) (based on this https://goo.gl/k5iZZJ ) which allowed for a bit more (maybe 1 or 2 minor divisions) display.

    Then I noticed that pressure on the bottom of the board or deforming/twisting the scopes frame will restore the normal width display (now out of calibration thanks to my trimming), so I suspect I have a bad solder joint somewhere (I suspect the high voltage system but I have a great deal of respect for 7kV)

    Before I go through a wild goose chase, anyone have an idea what I can narrow it down to?

    TIA, Dre
     
  2. 73's de Edd

    73's de Edd

    2,839
    1,207
    Aug 21, 2015
    .

    Sir erdrd . . . . .


    A good check for connections itermittency is with repeated tappa-tappa-tappa from the plastic handle of a small screwdriver . . . .while you watch the display vewy-vewy carefully.

    73s de Edd
     
    bushtech likes this.
  3. elebish

    elebish

    177
    12
    Aug 16, 2013
    Check the horizontal sweep output transistors and wiring going to the (side) pins on the neck of the crt. These crt's generally have electrostatic type deflection circuits that contain a voltage of about 200 to 300 dc. Be careful not to break these pins or the neck!
     
  4. vk2ipd

    vk2ipd

    2
    0
    Nov 11, 2009
    I have a very similar problem with my 2235. It has a reduced horizontal sweep (not sure if I am right). Actually, I can't see the display at all in normal operation but when I press the "Beam Find" I can see the beam. By keeping the Beam Find button holding and applying a 1 MHz signal from a Sig. Gen, I can see only vertical deflection but no sweep/ trace horizontally. Also, the horizontal screen is reduced in size and does not stretch to the full. What actually is the problem with my CRO and where should I start looking? Is it a Horizontal amplifier or sweep or trigger problem? Thanks in advance.
     
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