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cap tester repair

Discussion in 'Troubleshooting and Repair' started by pete g, Jan 8, 2019.

  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    When you get back to this, maybe R6 should be looked at more closely.

    Sorry we were not able to assist you more.
     
  2. pete g

    pete g

    79
    2
    Sep 14, 2010
    hi, the problem with this tester turned out to be phenolic wafer switches that have become conductive and leak voltage erratically. this was the result of me dousing those switches for years with contact cleaner. I never knew this could happen. live and learn.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    Oh, I didn't expect that. Did you find a solution for it?
     
  4. pete g

    pete g

    79
    2
    Sep 14, 2010
    no, I think this tester is gone. but, i'am going to use parts from it to build another.
     
  5. 73's de Edd

    73's de Edd

    2,644
    1,074
    Aug 21, 2015
    Sir pete geeeeeeeeeeeeeeee

    Hey ! Wa a a a a a i t. . . . . . . . .un momento . . .por favor . . . .
    As all . . . . . may not be lost.
    First of all, I TRULY think that THE fault will be with the units 18 (17) position large rotary voltage section divider switch, since it is he one that is INITIALLY and potentially subjected to having the highest DC voltage being across its sections.

    Lets try this simple, yet logical test initially. . . . . .

    I see that it is assigned with a nomenclature of . . . VOLTAGE SWITCH . . . . with no "SW" designation being given on my schematic . . . BUT . . . with it not being the DEFINITIVE schematic such as the units construction manual and / or parts list would be providing.
    Looking at the switch, you can see that its VERY highest voltage potential would be at the #17 rotor terminal and the #16 fixed switch stator contact.
    There is being a complete daisy chained loop of divider resistors from #16, on around to #1 which gets grounded via R15.
    This unit is of such age that it just might have had silver plated contacts and they have with time and chemical contaminants, developed a surfactal coating of silver oxide . .which would be a flat BLACK color.
    If you are in a humid / fog / smog or manufacturing (petroleum- chemical-paper mill ) oriented area, the potential for contamination via alkalinic acidic sulfuric agents in the astmospherics to the silver is exponentially accelerated. Additionally . . on the home front . . . if you consume a lot of beans,eggs and have this unit stored in your shop where you work and therein, do break wind a lot, . . . hydrogen sulfide . . . the switches silver plating is subjective to oxidation.
    Your worst mistake on a switch of this construction would be to flood the whole wafer with a spray aerosol type of cleaner with an suplemental lubricating agent. The silver oxide has a proclivity to break free and precipitage within the "oil slurry" to produce a spreading electrically conductive film.
    One should have cleaned this type of switch with a total degreaser and have left the phenolic / bakelite wafer totally clear of any residue and then the use of a toothpick to individually and selectively apply a clinging lubricant just to each moving contact set. With this HV level my choice would be Dow Corning Z5 silicone grease.
    Laymen can find it as plumbers clear silicone grease at better hardware stores . Multiple steps further on up the educational and food chain . . .chemists . . know it as being silicone stop cock grease.
    We now might consider that you either have a conductive slurry / film that is conducting an area of your switch to the ground infrastructure mechanically connected to it.
    Or a worse case, is being that a conductive micro path has burnt its way into a portion of the wafer.

    Lets now do this test to evaluate the voltage leakage situation . . .

    Loosen the front control and pull the switch from its being grounded to the chassis, as well as its connection from R15, at which ever of its ends that is easiest to free from its ground connection.
    If you then have the switch unit loose and only connected to the RED arrow HV DC source at pin # 16 and insulated from everything by its resting upon a plastic pad there should be almost full supply voltage at the free #1 end, if it is encountering no leakage to ground.
    Confirm if there is being leakage in that switch by powering up and initially reading the 600VDC at #16 and THEN measure to the control shaft, where there should be no voltage UNLESS there is being a leakage between one of the stator contacts and the metal infrastructure of the control mounting shaft and nut..
    Rotate between all of the settings of the switch rotor and check for voltage.
    If you do read voltage on the control nut and shaft, open your daisy chain at the halfway point in the area of R24 or 25 and place your switch rotor on the 600 V position of #16.
    If you still read voltage on the control nut, your leakage is being between mid position and your #16.
    Then, if non conclusive, further open the daisy loop by lifting R27 or 28 at the quarter way point.
    The highest probability is being on the highest voltage points of Switch #16-15-14-13..
    Once the leakage point to ground is located, I would degrease the whole switch with an acid brush cut down to 1/4 in bristle length to make it extra stiff and use a degreaser with zero trace oil or grease content, akin to denatured alcohol, xylene, acetone or MEK.
    If that doesn't open the leakage, due to a conductive oxide path then, the presence of a micro burn trace in a wafers phenolic would be the suspicion.
    You then might see if the unit can be powered down and if leakage can be read with an ohmmeter set on its highest range. If so, ohmically monitoring, while scratching across the phenolic with a sharp needle at a right angle to the suspicioned path, will usually open up and pinpoint a burn path, if its not being readily visible.

    I will wait for your results and after that, you would want to evaluate the REST of the unit by initially taking note of the voltage range that you experienced eye tube flicker .

    Then you take two *** 1 watt resistors (or a combination) and make a voltage divider resistor pair to create that voltage at their center junction.
    The high end of the resistor pair goes to the RED arrow wire that is disconnected from the VOLTAGE SWITCH. The midpoint of the resistors goes to the
    ORANGE arrow wire that is also now disconnected from the VOLTAGE SWITCH.
    *** Look at, and add up the daisy chained series resistances at THE needed voltage point, and you can compute the two resistance values being needed .
    The bottom resistor end connencts to ground.
    This simple voltage supply should then let you ignore any problem found with a potential leaking VOLTAGE SWITCH and see if you don't then get a flicker free eye tube tube operation.

    Thinking back . . . . as per . . . . your
    I hung a 22ufd cap on the line that feeds the bn8 grid. that got rid of the noise and also enabled me to calibrate the min lytic position. the mica,etc. position still is a problem. somrtimes it will calibrate, but then open again.

    Wherein, you found that the 22 ufd electrolytic at the 6BN8 tube filtered out erratic / random fluctuations , either down or completely abated them.
    That TEMPORARY TEST would THEREWITH confirm that your problem was not being on past the 'BN8 and 6E5 tubes circuitry.
    Needless to say though, it could not be left there in circuit, as in the bridge function, those tubes are being used as an AC amplifier.
    In leakage testing, they are being configured as a series, direct DC coupled amplifier circuit.

    I hope that you also interpreted my explanation that in the LEAKAGE testing that:
    The TYPE SWITCH Section B sequentially switches in different paired sets of "cathode resistors" for the 6E5. That series of adjustments establishes the test current value and they DO have to be set in proper sequence, with the 100K adjustable R43-44-45 sets initially being at their highest resistance settings to then be able to trim in the three 47K fixed values, to their proper settings.
    They also have to be set in a sequence as the other two settings are interrelated.
    Your TYPE SWITCH Section A is switching in the R34 - R35 and R6 voltage divider resistors to establish the 6BN8 voltage test ranges.

    If you do my suggested use of the two voltage divider resistors to do a dynamic test bypass of the . . . . suspect . . .leaky . . .VOLTAGE SWITCH.
    And have NO test capacitor across the test terminals in performing a LEAKAGE test, I feel that you will then see an open eye tube in all the three test types of capacitor positions and with no eye flicker, with now having a stable supply voltage presence.
    Then you could try 3 different test cap types and see if all is still well.
    If the VOLTAGE SWITCH outermost portion of its wafer was not the culprit and a good scrub down did not correct leakage , nor did you locate any micro burn trace.
    Then aditionally, you need to check the switches central button phenolic wafer that is being adjunct . . .periphally . . . . and internally, with both the rotor contact ring and the central grounded switch shaft.
    FACTOID . . . .
    You could always just use two insulated washers and a 1/4 in O ring to isolate the VOLTAGE SWITCH from grounding to the chassis by the control shaft and nut.
    The frontal plastic knob isolates your fingers in use / adjustment.
    If it electrically floats it can't leak any of its voltage to ground.

    What say ye . . . .?

    73's de Edd . . .
    . . . . . . . . . . . .

    A very, very crowded, maxxed to the limit elevator, smells quite different to a midget.


     
    Last edited: Jan 28, 2019
  6. pete g

    pete g

    79
    2
    Sep 14, 2010
    edd, once again thank you for your in depth reply. I have not tested the voltage selector switch for leakage. I know for sure the other two switches were conductive. those two switches I've been baking in an oven, to try to dry them out, the results so far have been promising. ie: no measurable leakage. will try the suggestions you have made and post back.
     
    (*steve*) likes this.
  7. 73's de Edd

    73's de Edd

    2,644
    1,074
    Aug 21, 2015
    The THOROUGH stiff brush down, with a STRONG degreaser would be the most important aspect of those units cleaning.
    Just using the SELECTIVE . . .PINPOINTED use of contact dope/silicone/lube should have them lasting with no voltage breakdown worries again.
     
  8. pete g

    pete g

    79
    2
    Sep 14, 2010
    I used acetone and dow corning z5.
     
  9. pete g

    pete g

    79
    2
    Sep 14, 2010
    i measured from 600v to control shaft .5-.7 volt. from 600v to wafer .3-.4v. this is b4 cleaning.
     
    Last edited: Jan 30, 2019
  10. 73's de Edd

    73's de Edd

    2,644
    1,074
    Aug 21, 2015
    Sir pete geeeeeeeeee . . . . .


    Looks like you have no problems there then . . . . .
    Additionally . . . . . . since they were KNOWING that VOLTAGE SELECTOR switch was going to have some quite high voltage potential across it, at one end . . . they may have opted in using a hard surfaced phenolic type for its wafers.

    I will further clarify that with a mechanical / physical analogy . . . . of a potter using clay.

    A product he made would be molded and then come out of the kiln . . . and it would have a flat bisque surface.
    If he opted to then coat it with a glaze and refire it again, it would then come out with a very hard smooth glass like finish.

    Likewise, with switch wafers, I have seen the wafers with the final glass like surface condition which would be fine in its insulative capacities.
    But having a switch wafer with that porous condition . . . . would be subject to absorption of contaminants.

    Your two other switch types may have used lesser quality wafers of the surfactally porous phenolic type.

    73's de Edd . . . . .
    . . . . . . . . . . . .


    I childproofed my house, but they still get in.
     
  11. pete g

    pete g

    79
    2
    Sep 14, 2010
    o.k., that's good news. i'am going to replace some resitors and start putting the unit back together. thanks for your input.
     
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