oscilloscope woes

Discussion in 'General Electronics Chat' started by tincat2, May 10, 2009.

  1. tincat2

    Thread Starter New Member

    Jun 7, 2007
    9
    0
    i recently acquired an os(leader 15mhz) and gave it a quick look-things seemed ok. today, i turn it on and while i get a sweep which is time variable, i can get no voltage variation-not even the square wave from the cal post. the machine just flatlines. have switched probes and various input sources. i am by no means proficient w/a scope-i got this to learn and to do some work on a receiver i want to rehab. if anyone can point me to possible causes for this problem, i be very grateful. thanx.
     
  2. DonQ

    Active Member

    May 6, 2009
    320
    11
    Did you bump the "input coupling"? Usually they have "AC/DC/GND" settings. If you bumped it to GND you'll never get any signal to the vertical amp.
     
  3. tincat2

    Thread Starter New Member

    Jun 7, 2007
    9
    0
    i pretty much played with all the settings, including a startup as per the manual and no go. but your reply has me thinking that, yes, the gnd position does kill the vert, so i'm going to look more closely at that pushbutton. thanx for the thought and i'll get back w/results after some z's.
     
  4. flat5

    Active Member

    Nov 13, 2008
    403
    17
    He sleeps a long time :)
     
  5. tincat2

    Thread Starter New Member

    Jun 7, 2007
    9
    0
    wish i could get as much sleep as i want,but that's another story.
    upon some thought, i remembered that this is a dual trace scope, and that i had gotten the same behavior off both inputs. i looked at things more closely and didn't see anything obvious-flatline(no vert deflection) on either input w/switches properly set-so it seems it must be on down the line somewhere. i did hook up the other scope i bought at the same time from this guy on craigslist, and in fooling around, i find that no matter where i probe, i get a trace similar to a sine wave w/about a 2v peak(i'll recheck that). this includes different components and the chassis. could something be shorting here or am i just not getting it. i will, as i get a chance, continue on with the tiny little letters and not too great a print job, schematic, to see if i can locate the common between the inputs w/ an output to the amp section. there is a vert preamp board and an amp board to this thing, so i figure the preamp is the place to start. help is always appreciated. thanx.
     
  6. flat5

    Active Member

    Nov 13, 2008
    403
    17
    You are in the "States"? Is it a 60HZ wave?
    You will get this on the 'scope if the ground is floating.
     
  7. DonQ

    Active Member

    May 6, 2009
    320
    11
    When reading "the square wave from the cal post", the ground is not an issue since both the circuits are internal to the scope.

    If both vertical amps are acting the same way, it is likely something that they both have in common. It is also likely that it is a component with the highest likelihood of failing. Fortunately, in this case they are the same component.

    Power supply, >90% probability.
     
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