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New project - 1967 oscilloscope restoration

Discussion in 'Troubleshooting and Repair' started by (*steve*), Nov 30, 2019.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Ok @73's de Edd, here's some voltages, all with respect to the chassis.

    The heater windings (pins 1 and 11) are at -515V and -513V respectively. Pin 11 is tied to pin 2

    The cathode (pin 3) is around 7V more positive than the heater due to the voltage drop across the 100kΩ cathode resistor (current is approx 70μA).

    G1 (pin 2) is tied to the EHT and is also at -515V

    A1 (pin 4) is at -303V

    The deflection plates on pins 5 and 6 are at 188V and 184V respectively.

    A2/G2 (pin 7) is at 88V

    The deflection plates on pins 8 and 9 are at 180V and 189V respectively.

    Pin 10 is N.C.

    And we're back to pin 11 that was mentioned above.

    The scope is in external timebase mode (effectively X-Y mode) with no signal and the trace is roughly centered (it's actually about 1/2 a division low and 1/5 of a division right)

    If I move the trace all the way to the top of the screen, the collages on the delection plates do this:

    5: 197V
    6: 165V
    8: 179V
    9: 184V

    All the way to the bottom

    5: 167V
    6: 195V
    8: 179V
    9: 183V

    All the way to the left

    5: 182V
    6: 181V
    8: 156V
    9: 203V

    And finally, all the way to the right

    5: 182V
    6: 181V
    8: 199V
    9: 160V

    Ok, and as I check the positions of the astigmatism and focus controls, I find they're labeled back to front!!!! AND knowing this I can adjust the trace to a fine point!

    IMG_20200104_214002_compress86.jpg

    The spot is a bit blown out in this image, it actually looks quite small.

    Turning on the horizontal timebase we get this

    IMG_20200104_214311_compress15.jpg

    And with a little tweak to the horizontal gain...

    IMG_20200104_214632_compress30.jpg

    Woo hoo!

    Now to rotate the tube a little too get the trace horizontal.
     
    bertus likes this.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I'm pretty happy with that

    IMG_20200104_220015_compress63.jpg

    I might grab a signal generator to see how well it works, but I really need to replace the line cord and put a plug on it before I do too much more.

    I'm pretty sure this isn't up to code

    IMG_20200104_220425_compress98.jpg
     
    bertus likes this.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Well, it does show a square wave.

    IMG_20200104_222344_compress73.jpg
     
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  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Hmmmm, but sine and sawtooth doesn't look at all good

    IMG_20200104_223144_compress61.jpg

    IMG_20200104_223126_compress80.jpg

    I suspect a problem in the vertical amplifier.
     
  5. bertus

    bertus

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    Nov 8, 2019
    Hello,

    That certainly looks like clipping on the lower side.

    Bertus
     
  6. BobK

    BobK

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    Jan 5, 2010
    Wow, impressive progress!

    Bob
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Damn, it seems to be working now :-(

    IMG_20200105_150213_compress17.jpg

    It seems like it was a switch contact issue because it went away after changing the vertical range a few times.
     
  8. BobK

    BobK

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    So, what are you going to do with it now?

    Bob
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I was going to convert it to a component tester.

    However some tests I've done in X-Y mode concern me a little. I think there may still be some fault hiding in there.

    Changes in the gain of the vertical amplifier seem to have an effect on the position of the trace. This needs more troubleshooting.

    The control at the rear clearly gives a few options for triggering, but the triggering doesn't behave like you would expect. I think that may be a feature though.
     
  10. BobK

    BobK

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    Jan 5, 2010
    I think a DC offset in the vertical amp would do that, right? Is there possibly a trimmer to null the offset?

    Bob
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    There are a few adjustments, but they seem to be trimmer capacitors. Also, the input is always capacitively coupled, so I don't see any reason why the coupling between the vertical amplifier and the differential delection plate driver isn't likewise capacitively coupled (but I haven't checked in any detail). Something to consider...
     
  12. BobK

    BobK

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    Jan 5, 2010
    Hmm... Never seen a scope that did not have a DC input option, but you have found one!

    Bob
     
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