Connect with us

Tektronix 2245; need help with dead PSU

Discussion in 'Electronic Repair' started by Alfred Green, Oct 21, 2003.

Scroll to continue with content
  1. Alfred Green

    Alfred Green Guest

    Greetings,

    My 2245 'scope recently died, with no outputs from the psu. The input
    cct seems ok with ~150vdc across the filter cap, but I'm having a hard
    time tracing the voltages any further without a schematic.
    Does anyone have such a thing, and/or tips on what to be looking for?
    In case there are different versions, the psu board has a 1986 date
    code and uses a MC34060 pwm chip.

    All comments welcome,

    Alf in Scottsdale, AZ
     
  2. Jim Yanik

    Jim Yanik Guest

    (Alfred Green) wrote in
    ISTR that the 2245 service manual has schematics for the PS.
    Ebay or big-list.com may turn up a manual.
    And you can download a datasheet for the Motorola MC34060 IC probably at
    the Motorola website.
    You can ohm the switcher FET (open?)and any rectifier diodes(short?),check
    the electrolytics with an ESR meter.
     
  3. Techie

    Techie Guest

    I might be able to help.
    i have a manual for something like this.
    might just be the same one.
    will let you know later.
     
  4. Alfred Green

    Alfred Green Guest

    I spoke to someone at Tektronix and he confirmed that the service manual
    does include the schematics. They no longer have anything available however.
    A net search has failed to uncover one either so far. I have found one for
    the 2246; I wonder if it used the same psu as the 2245.
    I have that info. Checking the vcc wrt the ground pin shows the voltage
    varying from 0 to +5v; lower than I was expecting and I'm puzzled why it
    would be changing.
    The input switcher is an IRF830 which I think is enhancement mode, so I cant
    really check that without supplying gate voltage. The diodes and caps seem
    ok, but testing them in-circuit could be misleading.

    I'll keep on exploring, and I appreciate the comments.

    Rgds, Alf
    Scottsdale AZ
     
  5. Techie

    Techie Guest

    I found my Service manual and its for a 2445A
     
  6. Jim Yanik

    Jim Yanik Guest

    Yes,it does.(I coulda told you TEK would nothave the manual;the 224X series
    has been 'obsolete',or past the 'Long Term Support Period' for several
    years now.)
    The 'housekeeping' supply for the IC is started by a cap charged by a
    resistor from the rectified line V supply.The cap charges,the IC tries to
    start,but the xfmr winding that maintains the 'houskeeping' supply cannot
    supply current,perhaps because the switcher FET is open.
    That ESR meter (Dick Smith meter!!) is invaluable for testing in-circuit
    electrolytics,especially for switcher supplies.
     
  7. Jim Yanik

    Jim Yanik Guest



    Not the same family of scopes. No similarity at all.
     
  8. Alfred Green

    Alfred Green Guest

    Thanks. I've ordered a CD for the 2246.
    That makes sense. I'll dig out one of my old scopes to look at it, just
    using a DVM may be giving me a false picture.
    I may just replace the FET anyway and see what happens.
    Sounds like a good investment!

    Tnx, Alf
     
  9. Alfred Green

    Alfred Green Guest

    It looks like there are some similarities, but not quite enough. I
    appreciate your efforts in sending me the diagram; I'll keep it for future
    reference.

    Tnx, Alf
     
  10. Jim Yanik

    Jim Yanik Guest

    The 2245 and the 2445 and A versions are nothing alike.
    Two entirely different families. Different architectures.
    Now,2445 and 2465 (and A,B versions)are very similar;and 2245 and 2246,2247
    are very similar.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-