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Tektronix 2445 Readout is no good , video included

Discussion in 'Electronic Repair' started by [email protected], Nov 14, 2007.

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  1. Guest

  2. Jim Yanik

    Jim Yanik Guest

    2445 non-B scopes have separate R-O boards.
    the signal from them feeds into the vertical on the main bottom board.
    try swapping the readout boards.
    IIRC,there's also a pot to adjust R-O crawl/jitter.
    see the cal procedure in your service manual.

    On "B" models,the readout is integrated to the A5 uP board.
    "B" model A5 uP boards are NOT swappable with earlier versions.
     
  3. JW

    JW Guest

    I'll second what Jim has said with regards to the jitter pot. On very
    early serial numbers, the pot and a few passive components were tack
    soldered to U800 (An ECN I guess - I just replaced a U800 on a 2465 that
    had this). On later serial numbers, R805 was added to the A1 board. It
    couldn't hurt to give it a twiddle.
     
  4. Guest

    tried play with jitter , didn't do the trick ...

    and you are right about A5 in the 2445 , the R-O is not on this
    board , i just did a swap with a good 2445 A5 and got the same jerky
    readout .

    what component is making the problem in the R-O of the 2445 ?
    caps ? or something else ?
     
  5. Jim Yanik

    Jim Yanik Guest

    possibly caps,or a bad hybrid on the main board.
    Does it twitch in the vert or horiz direction,or both? signal trace
    solid,in both V and H axes?
    This may be where you have to scope every decoupled PS supply line.
    could even be some of those 0.1uf DIP caps that are all over every board.
     
  6. Guest

    trace is solid , no trace problems .

    and one thing i noticed , when i control the read out intensity fully
    CW , the R-O shifts upwards ...
     
  7. Jim Yanik

    Jim Yanik Guest

    Is that a trace with a signal displayed,or just the baseline trace?
    With a signal displayed,you can see any horiz jitter.
    Without an input signal,you can't see any jitter in the horiz.
    I wonder if your CRT is maxed out on intensity.(grid bias)
     
  8. Guest

    i'l try with a signal later on ...

    and i adjusted the grid bias , its fine .
     
  9. Guest

    Well , the read-out is good now , i replaced the power supply , and
    don't have jerky read-out .
    i guess power supply ain't that good .

    but i got another problem with this scope , the horiz is not good at
    some of time bases , some of them ok , but lets say 5u is drifting .
    i did CAL 01-04 , but got LIMIT warning in the horiz section , could
    not adjust as required .
    something is wrong , what i'm doing wrong ?
     
  10. Jim Yanik

    Jim Yanik Guest

    probably marginal electrolytics,bad ESR.
    often,the PS is the source of trouble appearing elsewhere.
    All the parts for timing are on the sweep hybrids.try swapping the A and B
    sweep hybrids,and recal.if the problem goes away on that range/mode,then yu
    have a bad hybrid.
     
  11. Guest

    Well , gonna try this after i'l find new U800 (Horiz amp ) just
    destroyed the one that was on the scope .

    the horiz amp got nothing to do with the timing ?

    do you know where i can find U800 ?
     
  12. Jim Yanik

    Jim Yanik Guest

    they aren't made anymore,and the only place you can get one is from another
    2445/65 scope.IIRC,there was an Ebay seller who had some salvaged ones for
    sale,but the price was pretty high.
     
  13. Guest

    i'l try to salvage ...

    the horiz amp got nothing to do with the timing ?
     
  14. Jim Yanik

    Jim Yanik Guest

    why don't you read the excellent circuit description that's in the service
    manual?
     
  15. Guest

    Well all good now , replaced U800 , replaced hybrids , timing is
    good .

    great , thanks .
     
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