+ Post New Thread
Results 1 to 7 of 7
  1. #1
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Sep 2019
    Posts
    4
    Helped
    0 / 0
    Points
    28
    Level
    1

    Beckman Industrial 9020 - Poor focus with no adjustment

    Hi.

    I've just bought myself an old scope (Beckman Industrial 9020) for a bit of DIY testing on some circuits I'm building with the kids.

    Really nice bit of kit, and all seems to work, except the focus is shot (large disks visible instead of small dots for Ch1 and Ch2) and also the intensity knob makes a slight difference to the brightness.

    Of the two issues, the main one is the focus as that prohibits the real use of the scope and I suspect that fixing this may bring the intensity into line.

    It seems that the OPPOSITE problem was solved in March 2009 (ooops, over 10 yrs ago now!) where the OP had good focused, but no intensity/brightness control.
    Previous thread link - https://www.edaboard.com/showthread....0-oscilloscope

    The fix had been proposed by Chris Williams (Chris56000 - https://www.edaboard.com/member.php?201035-Chris56000) who seemed to have detailed knowledge of the componentry and workings of the scope.

    In a way, I'm reaching out to see if this fellow is still around (not too far from where I live in Birmingham, UK) and happy to assist.
    Any other assistance would also be gratefully received!

    Thanks
    Affy

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 81,438, Level: 69
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,351
    Helped
    4457 / 4457
    Points
    81,438
    Level
    69

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    You almost certainly have an open circuit resistor somewhere around the CRT controls. Excessive brightness may also cause the focus defect, it may be pushing the CRT so hard that it can't actually produce more light but the electron beam is passing the focus anode so fast it doesn't have chance to converge the beam.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  3. #3
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Sep 2019
    Posts
    4
    Helped
    0 / 0
    Points
    28
    Level
    1

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    Thanks betwixt.

    I'll take a look, but concerned about the VERY high voltages I may encounter!



    •   AltAdvertisement

        
       

  4. #4
    Member level 5
    Points: 1,016, Level: 7

    Join Date
    May 2017
    Location
    Canada
    Posts
    84
    Helped
    39 / 39
    Points
    1,016
    Level
    7

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    Service manual (in French): The Boat Anchor Manual Archive (BAMA), Beckman 9020 has schematics



  5. #5
    Super Moderator
    Points: 81,438, Level: 69
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,351
    Helped
    4457 / 4457
    Points
    81,438
    Level
    69

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    I'll take a look, but concerned about the VERY high voltages I may encounter!
    To some of us those are quite low voltages, only 2KV!

    Seriously, switch it off first and give it a minute or two to discharge capacitors then just start measuring resistances. Download the manual, the problem is almost certainly on page 43 in the bottom right corner (with it rotated so text is the right way up).
    My first guess would be that one or more of R559, R560, R561 or R563 has changed value. If they need replacing, make sure you use high voltage rated ones.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  6. #6
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Sep 2019
    Posts
    4
    Helped
    0 / 0
    Points
    28
    Level
    1

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    Quote Originally Posted by prairiedog View Post
    Service manual (in French): The Boat Anchor Manual Archive (BAMA), Beckman 9020 has schematics
    Thanks... and downloaded.

    Was thinking about needing a French class to read the manual, but at least circuits diagrams are non-language specific!



    •   AltAdvertisement

        
       

  7. #7
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Sep 2019
    Posts
    4
    Helped
    0 / 0
    Points
    28
    Level
    1

    Re: Beckman Industrial 9020 - Poor focus with no adjustment

    Thanks betwixt

    I've opened her up and going in with a multimeter...
    Not looking for HT voltages yet!!! just going to take your advice, allow it to discharge and then test resistances in the first instance.



--[[ ]]--