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Tek 2235 Good Focus but High Intensity

Discussion in 'Troubleshooting and Repair' started by DB20Bogen, Oct 26, 2015.

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  1. DB20Bogen

    DB20Bogen

    3
    0
    Oct 26, 2015
    I have a Tek 2235; the trace focus is sharp and the focus control exhibits a normal range of control. However the intensity control has no effect (trace is at max. intensity), retrace is dimly visible. The the voltage across 510K resistors (R888 315V, R889 310V, R890 313V R891 309V) in the focus divider are reasonable. All other scope functions are normal. Suggestions??
     
  2. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Any effect of horizontal modes A,ALT,B ?
    Have you tried operating the Z-axis ?

    Do you have another scope to debug the faulty one?
     
  3. 73's de Edd

    73's de Edd

    3,070
    1,299
    Aug 21, 2015
    .


    Sir . . . . . .DB20Bogen . . . . . . (And 'ole Bogen amps don't require this high degree of instrumentation sophistication.)

    How about a cold dead set condition and measuring that series string of resistors again as per their resistance readings and ALSO include the one at the very head of the supply on the HV side and the low side of the focus supply as R894 which is being . . . . . guess what . . . yet another 510 K.


    Went into my "mule barn" archives and pulled its schematic and then UNITIZED it into one cross page flowing unit, instead of its two pages in the manual.
    I think that it will cover all of the situations relevant points of interest, and provide us with a shared reference schematic .


    Schematic referencing:

    [​IMG]

    Off site Access as:

    http://i.imgur.com/k2xMB8v.png



    73's de Edd


    .
     
    Martaine2005 likes this.
  4. shrtrnd

    shrtrnd

    3,808
    511
    Jan 15, 2010
    Did you check to see if the intensity control pot itself is bad?
     
  5. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Ed,
    Those resistors are related to focus.
    The intensity issue is totally different!
    It is at pin number 3 of the CRT.

    DB20Bogen,
    Please respond to my previous reply ( #2).
     
  6. DB20Bogen

    DB20Bogen

    3
    0
    Oct 26, 2015
     

    Attached Files:

  7. DB20Bogen

    DB20Bogen

    3
    0
    Oct 26, 2015
    Thanks for the response, all the 510K resistors are in tolerance. My other scope is a Tek 549 but that's still late 60's
     
  8. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    DB20Bogen,
    You should use the Tek 549 to debug the 2235.

    Forgot to ask:
    Any effect of A or B intensity knobs? (I assume none,just making sure).

    Look at the attached pics
    You should check the waveforms with 549 Probe GND to chassis of 2235.
    Warning : HV presnt in the area !

    1.Check waveform 48 - Before you check with the 549 scope ,use a DMM and make sure you don't have High-Voltage(over 100V) on it!(could be in some fault situation).
    2.Check waveforms 47,46,45.

    Compare to the pics, and please let us know what you find.

    2235-1.jpg 2235-2.jpg 2235-3.jpg 2235-4.jpg
     
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