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Tektronix 2445 readout problem

Discussion in 'Troubleshooting and Repair' started by bobby2445, Dec 17, 2010.

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  1. bobby2445

    bobby2445

    1
    0
    Dec 17, 2010
    Picked up a Tek 2445 with a few problems, maybe someone can provide some guidance.

    When I first turned it on, the display and alpha-numeric readout was barely readable and it gave an error message (did not write to down). The readout quickly descended into a jumble of unreadable and shaky blur. The trace was not straight, sort of 45-degrees slanted, barely visible, and the focus did not appear to do much.

    I tore into the unit, and found 2 blown caps on the inverter board (180uf @ 40v). I replaced those and a few around them.

    After reassembly and adjusting the astigmatism control, the readout was very readable for a brief time, maybe 15 seconds but then it collapsed into a similar jumble of mush again, although the focusing is quite good now -- while the readout is a jumble, you can tell that it is focused. The trace is also straight now, but not as crisp as a Tek should be.

    Playing with the "Readout Intensity" control seems to make the readout go all goofy, more or less randomly shaking up the jumble on the screen. Also, the astigmatism control seems to affect it also.

    Photo of symptoms:
    http://s127424922.onlinehome.us/2445-1.jpg

    Photo of caps that I replaced:
    http://s127424922.onlinehome.us/2445-2.jpg

    Assistance would be welcome. No need to make disclaimers about high voltage or whatever, I understand....
    Thanks in advance for your guidance.
    bobby

    UPDATE:
    Fired it up today, after sitting overnight:
    http://s127424922.onlinehome.us/2445-3.jpg

    BUT -- that lasted about 1 minute or so before collapsing into the jumble of blur.


    And I also discovered that in Delay mode the readout stays readable (been solid for last 30 minutes):
    http://s127424922.onlinehome.us/2445-4.jpg
     
    Last edited: Dec 18, 2010
  2. cj_elec_tech

    cj_elec_tech

    62
    0
    Oct 7, 2009
    Hi. In the image 2445-2, does the RENCO inductor closest to the edge of the board have a 'melted' section near it's right-hand leg - or is this just a trick of the lighting?
     
  3. cj_elec_tech

    cj_elec_tech

    62
    0
    Oct 7, 2009
  4. shrtrnd

    shrtrnd

    3,734
    478
    Jan 15, 2010
    Don't have a manual right now.
    What I remember is you've got a 4 channel storage scope.
    Biggest problem I've seen is the actual push-button switches failing to engage or disengage.
    When one switch gets stuck, it locks-out the other functions.
    If you can, get at the switches (the push-buttons are connected to slide switch assy's),
    and spray them with contact cleaner.
    My best guess from past experience, is one of your slide switches is not fully disengaging,
    locking-out your other functions.
    Spray out the pot assy's too.
     
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