Connect with us

New project - 1967 oscilloscope restoration

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

Scroll to continue with content
  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I decided to try to figure out what the switch at the rear is doing. So I started tracing some of the circuit.


    Ok, so I haven't got far yet, but that resistor between the two cathodes of the 6DJ8 looks interesting. Especially interesting because it seems to be connected to a screwdriver adjustment for horizontal gain, and because it varies when the position put is adjusted.

    Here is the back of that control


    The green and white (with green stripe) go the the two cathodes of the 6DJ8.

    And the control from the front does this

    IMG_20191207_125155_compress9.jpg IMG_20191207_125159_compress12.jpg

    Should it really do that?


    Looks like there's gunk in there. I'm pretty sure they're supposed to turn independently!

    Oh well, interesting sidetrack they leads me to something else to fix.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    A slightly more complete schematic. It shows the connection to the switch at the rear. I'm not sure how much sense it makes, but, it might have something to do with triggering.

  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    One more cap replaced


    Where are those other capacitors...
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    And another one... Luckily I've been able to find some suitable caps.


    And no, of course I didn't touch the capacitor with the soldering iron. Really. No, nothing to see there.
  5. bushtech


    Sep 13, 2016
    lol. I have always wondered what those marks on my caps are:D
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Still waiting on the high voltage caps (they will be shipped on 20 Dec -- so I might get them for Christmas).

    Meanwhile, the last of the other caps has been replaced


    No funny marks on this one!

    A question:. I replaced a 10uF 160V cap with a noname 10uF 450V cap. Now I've received the 10uF 200V Nichicon cap, should I replaced it again with that?
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The 2kV caps have arrived!


    Looks like I'm going to have to make a bracket...
  8. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Steve . . . . .

    In analyzing and . . . . . then winning out In my minds eye, is the adhesive bonding together of the lengthwise ends of the set, with their wire leads arranged pointing topside up.
    Then, in looking at the chassis real estate distance being available from the frontal foreground edge to the far distance of the RED glyptal tipped
    machine screw stud, looks like they should just fit in between those limits.
    Thereby . . . . . even evading the far ends minimal heat received, as is being radiated from that ends adjunct 9 pin miniature tube.

    Viewing the new poly units casing, somehow, a gut feeling is also telling me to avoid any and all metal, and incorporate the use of an all Plexi ?-----Lucite ?-------Polycarbonate ? support / mount for those new HV units.
    One can see that the old oilfilled can incorporated, spaced out and LIBERAL sized Ceramic / Porcelain slick glazed insulators.

    73's de Edd . . . . .

    My wife is such a bad cook, that in my household, we pray AFTER the meal.

  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I was contemplating a short aluminium bracket with cable ties to hold the caps to it.

    There's just enough room to place the caps with the long sides facing each other. I was thinking about a metal shield (not touching the capacitors) to protect them from heat.

    I could laser cut some acrylic, but it gets soft when heated, so I'd prefer to use metal.
  10. 73's de Edd

    73's de Edd

    Aug 21, 2015
    There's just enough room to place the caps with the long sides facing each other.

    If I'm interpreting that correctly . . . dimensionally, that would be my second choice of arrangements option.
    The bottom caps leads point upwards and the second caps leads point downwards.
    That leaves the one end of the caps to be joined with their outer foil connections.
    The caps other sides . . .inner foil leads . . . are spaced up high enough with the lifting upwards of the top capacitor, to
    achieve the proper distance for the inner " filter" resistor to fit in.
    Then that leaves the initially directly joined leads as ground and the opposite capacitor leads as HV in and HV out.
    Mounting with a flat Acrylic plate to have the caps adhered to it and spaced up from the chassis bottom, accordingly.
    That just needs a rectangular plastic plate and a possible metal bracket at the botttom monting.
    OR making a heated 90 degree bend, at the bottom of the plastic.
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I've removed one of the brackets holding the existing cap.


    The other end of the bracket prevents me from placing the caps as far back as I want to. I can't be bothered removing it right now though

    This is how I was planning to position the new capacitors.


    There ends up being about 20mm between the cap and the closest tube.
  12. bertus


    Nov 8, 2019

    Perhaps you can flatten the bracket, so the caps can be moved back a bit.

  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I'm going to have to make an entire new bracket. The existing one grips a ridge on the bottom of the original cap. The new ones don't have that ridge so a different method (and shape) will be required.
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I've gone through a couple of iterations in my head as the how to make a bracket.

    I've currently settled on an acrylic frame with some sort of metal heat shield.

    After removing the original capacitor, this is what I have:


    The old capacitor has measurable leakage, reading about 3MΩ after a long wait. There new caps rapidly rise beyond the approx 30MΩ my meter can read.

    Here is my MDF prototype bracket:


    That assembled looks like this:


    Fits like this:


    And with the capacitors:


    The various cutouts provide for a cable tie to hold the capacitors in place:


    The acrylic version looks like this:


    And assembled:


    Roughly in place


    There's still a few modifications to the bracket for strength, but it's looking close.
    bushtech likes this.
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Here's the final design, it securely holds the capacitors in place


    There's an acrylic version of this and I'll post some photos when I install it.
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Having built something to hold the new capacitors, I need to make a shield to protect them (and the acrylic) from heat.

    The first template was tested in a paper version


    Placed around the bracket it looks like this


    And that's kinda what I want, it stands away from the bracket. Hopefully heat transferred to this will either radiate away, or transfer to the case.

    After a few small modifications, I cut a version out of brass


    Folding brass is a little more challenging than paper, nevertheless, it came out pretty well


    The tab was used to solder the shield together.

    Dropped into place, it looks like it will work


    So it was screwed into place


    And the valves reinserted


    There's not a lot of clearance to the high voltage rectifier, actually it touches it. A bit of a quick tweak, and it doesn't any more.

    Now I can wire up the capacitors


    The high voltage connections look like they're sticking way up in the air, but actually they are at the same height as the connectors on the previous capacitor.

    And the anode cap is put back on with the cable having plenty of clearance.


    Almost ready to test!
    Last edited: Dec 31, 2019
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It's alive!


    The trace is very blurry despite playing with the focus. Setting the horizontal to external input gives me a spot that is nothing like circular either.

    I guess I have some more work ahead of me.

  18. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Steve . . . . .

    Seems like I didn't intrerpret it within your text on the units FOCUS aspects current operation .
    But, is the available focus pot AVAILABLE range letting the focus spot come into range . . . . and then optimizing . . . . and then proceeding any further, makes the spot start to go progressively into poor focus again.
    Or , per chance, is the optimum, being at / towards either of the end ranges of the pot, such that you might actually need further voltage adjusment to get / reach into optimum focus ?
    If such is the case, view the top reference to pick out the two RED X positions on the end terminals of the focus pot.
    If you were to break connection and insert an ~ 1 meg fixed resistor in series, that should shift the actual FOCUS pot range associated with that particular end, as you try each end at a time.



    From a second aspect, since we don't seem to have a proper reference schematic for this paricular scope.
    I did not see any astigmatism control adjustment of the G2 / A2 elements for the scope, with them just possibly having selected two voltage divider . . .fixed resistors . . . then feeding out from their junctions.

    Considering that is being a 3KP1 or compatible, check its pin 7 and examine to figure out their voltage feed circuitry to it.
    Then, see if the incorporation of a wired in pot . . .as per the sub schema . . . .will let you then alternatively adjust between THAT pot and the FOCUS pot to get a more improved pinpoint trace / spot.

    Also, you never confirmed the ID of the kine being used . . . .and for sure . . . there is not going to be a trace rotation adjustment, so you are left to loosening the kine clamp to let you mechanically align your now tilted trace with the scopes reference graticule.

    Thaaaaaaaaasssssit . . .

    73's de Edd . . . . .

    All the world is a stage . . . . . and most of us are being DESPERATELY unrehearsed.

    ASIDE . . .

    AC Supply Center

    POWER Laser cut finger joints on the case ? or just a good mechanical saw cut jig ?

    .Combo Phillips screw with molded on washer . . .or . . . Flat Phillips head screw set into a cup finishing washer ?

    ITS CONTROLS . . .
    Variac . . . Rocker Breaker . . .Rocker Main Power switch . . . .AC plug receptacle with its own individual power switch.

    LOVED that very compact Flood / Spot lamp, used them in the '90's from Philips, but no longer can find them.
    Last edited: Dec 30, 2019
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It's hard to say. The best focus is certainly near the end of the pots travel. I'm uncertain if it gets a little worse at the very end. At a minimum, the best focus shouldn't be so close to one end.

    I will try that, but first I will check some voltages to make sure they're what I expect. The fact that I still had the dim bulb tester in series is a potential factor. However the line correct is cracked in many places and I don't want to risk a short.

    There is an astigmatism control on the rear.

    I'll check the voltage range anyway.

    Yeah, it looks like trace rotation will be performed by rotating the crt.

    Laser cut

    Yep, screwed into an internal wooden frame

    Yes, yes, and yes.

    They're the only ones I can easily find now. Halogen bulbs are available, but they suffer if used at low power.
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    @73's de Edd here is a look at the insides


    One of the screws is visible.

    What you can't see is the input socket and the line fuse.

    Note that the circuit breaker is also on the input to the autotransformer. In retrospect, it should probably have been in the output.
    Last edited: Dec 31, 2019
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