Oscilloscope Repair

Discussion in 'General Electronics Chat' started by nDever, Jun 24, 2014.

  1. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Hey Guys,

    I've got an HP 1741A 100MHz dual channel analog storage scope, and it was working relatively well until one day when I went to turn it on and there was no signal coming up. It takes a few moments to warm up anyway, but this was longer than usual. I popped the top to see if I could find anything, and I found this IC-like connector part missing a pin. It looks like some type of ribbon connector. Sorry for the lack of focus in the photos.

    Anyone have any ideas or know where I can possibly get a replacement part? It's a good scope and I would like to save it if possible...

    145445.jpg
    145501.jpg

    The persistence button is also loose, but I think that's just a fastener problem. Shouldn't be too much trouble.

    145424.jpg
    145434.jpg
     
  2. dougc314

    Member

    Dec 20, 2013
    38
    11
    If your scope was working there is no reason to suspect that you just lost a pin. As for spare parts you'll need a doner scope.
    Do you see a trace?
    If you adjust y position and x position to max and min, can you see anything? Is there a beam finder button? if so push it and see if you can get a dot.
    Is there any indication of triggering? - Try Auto or line

    What can happen to cause loss of trace
    High voltage supply for CRT fails
    Driver in X or Y deflection fails, causing trace to be off screen
    CRT heater failure.
    Sweep circuit fails (still get a dot though, usually)
    Great news - Agilent has a PDF of the service manual
    http://cp.literature.agilent.com/litweb/pdf/01741-90911.pdf
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,394
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  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    I have an HP1741A myself that I repaired (A capacitor exploded and corroded a large section of the timebase board), and I believe that ribbon connector/DIP socket is normal. It is most likely not the problem.

    Was the scope acting strange before it stopped working? What exactly is it doing now? Are you sure the trace isn't simply off the screen? (Adjust both the vertical and horizontal position to see if you can locate it). Also try the beam finder.

    A video would be extremely useful here.

    Regards,
    Matt
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The service manual is readily downloadable for free. Just Google the model number.
     
  6. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Thanks for the insight, guys. I'm not at the workbench at the moment. I'll test it asap.

    @DerStrom8
    I don't recall it acting strangely before it stopped working.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Get set for some fun trouble shooting.
    You will need some tools:

    Service Manual, i.e. circuit diagrams
    DMM
    camera to post pictures
    Do you have a working scope?:p
     
  8. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Eh...no. :rolleyes:
     
  9. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Hey Guys,

    I did bit of digging yesterday and it turned out that the DIP header was the problem! I also re-soldered some cold joints on some of the control pots. A big thanks to all.

    092249.jpg
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Can you elaborate on what you did to the DIP header in order to fix the problem?
     
  11. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    I was afraid of that... :rolleyes:

    I soldered a piece of 22 AWG to the broken pin. A bit unorthodox I think.
     
  12. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Next question. How did it become broken in the first place?
     
  13. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Fine, I admit :(. When I went to look inside the first time, I may have pulled too hard on it.
     
  14. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Thanks for owning up. DIP pins don't just fall apart on their own accord.
     
  15. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    OK guys,
    I've got another problem and It's not my fault this time; I suspect a bad IC. The scope seems to be stuck in Store Mode. Does anyone know where I can find the schematic for this scope (if it's available)?
     
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