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Tektronix 2465 Oscilloscope problem

  1. Mar 30, 2016 #1
    So I have a vintage analog TEKTRONIX 2465 Oscilloscope that I bought used on eBay for a bargain of $300 last year. When I got it worked okayyyyy except when there was no input the CRT would display Channel 1 and 2 lines slanted and pressing the BEAM FIND button didn't help(nor adjusting the display controls). But last week I turned it on, then used the probe to an AC power supply I have and I saw this(no control adjustment helped):

    3FPhONL.jpg


    Now someone over at electronics.stackexchange.com suggested it might be a bad capacitor in the horizontal sweep amplifier. So I took it apart for further inspection and the CRT(made by Tektronix) was stamped with the manufacturing date of 3/23/83. That's 33 years, folks! I do wonder if the CRT might have gone bad(not sure what the average lifespan of a cathode ray tube is and particularly for an oscilloscope).

    Now have a USB oscilloscope probe but what do you need to connect this machine to a PC since it has digital outputs in the back? Does anyone here know how to interface the digital control computer of these devices?

    Any help would be most appreciated.
     
  2. jcsd
  3. Mar 30, 2016 #2
    Might I add: There is a place called Norway Labs that will fix these machines but for a flat rate of $970.00(:nb)) plus an additional $400 if it needs custom replacement parts.That's WAY too much money compared to what I got it for and I say repairing it myself will certainly be a learning experience.
     
  4. Mar 30, 2016 #3

    berkeman

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    What does this mean? Did you connect the 'scope probe and its ground clip to AC mains voltages? That can cause damage (not to mention a shock hazard). Hopefully you mean you connected it to a low-voltage AC signal.

    What is your electronics background? Have you worked with AC Mains voltages before? How about higher voltages like are used in the CRT? Can you tell us why it's important to connect an isolation transformer between the instrument you are repairing and the AC Mains wall power socket? :smile:
     
  5. Mar 30, 2016 #4
    It means I connected it to a LOW voltage AC power supply(40V, 5amps) with a 150Mhz probe(that has a 1MOhm resistance), not to an AC mains voltage. And it worked just fine afterwards.
     
  6. Mar 30, 2016 #5

    berkeman

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    Good! That's a relief. The probe would have probably vaporized anyway. :smile:

    What about the isolation transformer question? The 'scope may have one built in anyway, but you would need schematics to know for sure. Have you looked for the service manual for it yet? You should be able to find copies online, I would think.

    BTW, is the Beam Find button pressed in the picture that you took? Is it maybe stuck? (I've had a Tek curve tracer that is about 15 years old that had a couple buttons go goofy -- it was hard as heck to figure out what the problem was. Eventually by pressing the buttons a bunch of times, the contacts cleaned up enough to restore operation.
     
  7. Mar 30, 2016 #6

    The isolation transformer is to prevent electric shock during electronic testing of a device that uses AC power. And yes, I have the service manual and am just starting to read through it(it's a 256 page eBook) but I am wondering if anyone here who works with oscilloscopes has seen problems like this before.....
     
  8. Mar 30, 2016 #7

    berkeman

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    Well, that's what the display typically looks like when you push the Beam Find button, at least to me. Any chance it is gummy or gone bad? What happens when you push the Beam Find button now? Does the display stay the same, or does it get even smaller and brighter?
     
  9. Mar 30, 2016 #8
    Tried that. No luck. And there's no waveform when I connect the low voltage AC power input either. ><


    This image here is what you should see when the machine is powered up and there's no input signal(which is how it was when I got it except I only saw 2 lines instead of 4):

    2465A.jpg
     
  10. Mar 30, 2016 #9

    berkeman

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    What do you see when you use the calibration output to test the inputs?

    If you push the Beam Find button and the display still looks like that, I'd start tracing that Beam Find path to figure out why it seems to be stuck.
     
  11. Mar 30, 2016 #10

    jim hardy

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    I went to Ebay and found the Tektronix service manual for my 2211. Cost me $40.
    I need one for my Hitachi V422.
    Bought both scopes as scrap metal for 30 cents a pound so a few bucks more on manuals is a good investment

    I'd say you'll enjoy really learning the 'scope but to do that one must equip himself with the book on it.
    2465 it would seem is a sophisticated computerized machine

    In vacuum tube days you could look inside and tell what every pin was for, plate cathode or grid and figure out from that how it worked.
    We traded that marvelous simplicity for the phantasmagorical capability of embedded computers.

    I'd open it up and blow out all the dust first thing.
    Good luck
    old jim
     
    Last edited by a moderator: May 7, 2017
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