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telequipment d66a scope problem

Discussion in 'Repairing Electronics' started by techmanx, Nov 30, 2008.

  1. techmanx

    techmanx New Member

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    HI, anyone out there who has repaired these scopes or has a good idea of the problem area I should be looking to solve the problem that this scope now has?
    I know the scope is old, but the last time I used it three years ago it was in perfect spec. I have now a need to use the scope and I find it has the following problem:
    All functions of the scope work OK except for the scan.
    The scan operates as normal except that it scans only to half way across the tube. The width and expander controls are OK but will not bring the trace to full tube face coverage.
    I have a manual for the scope on the way to me so that I will not be completely in the dark, but it would be most helpful to have a good idea of where the problem lies! My guess at the moment is that the X scan drive voltage has gone down or low!
    So if you can help please do, many thanks in advance, Brian
     
  2. user_88

    user_88 Member

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    ... could be related to a defective capacitor .... Electrolytic capacitors in particular tend to age ... by drying out ... leaking ... losing tolerances.
    ... It might be possible to just allow the scope to 'warm up' for a length of time ... hours...days... Turning it on and plugging it in. It has been said that electrolytics can 'recover' ....I haven't actually witnessed this phenomenon... it probably depends on the severity of their condition.
    If still no luck, remove the case cover and examine the electrolytic caps for obvious burns or other defects ..... remember to discharge them properly before handling them, if you decide to remove them for examination.
    If the problem is not an electrolytic capacitor, that would be more difficult to locate.
     
  3. techmanx

    techmanx New Member

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    defective caps

    Yes I think you are probably on the right lines, I will leave it running for a few days, then when nothing improves, I will dig deeper (when my circuit diagram arrives!). Many thanks for your comments, regards, Brian
     
  4. dave

    Dave New Member

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  5. user_88

    user_88 Member

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    After glancing at a generic scope schematic ...
    Your schematic, when it arrives, should have a section labeled Horizontal Amplifier, or something similar .... This would be one possible section to examine for problems .....
    Another possibility would be to verify the DC power supply voltages, to be sure that they are all present ...
    If you have to remove the main circuit board ..... there are certain precautions to be aware of in disconnecting the high voltage wire from the CRT tube ....
     

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