Grounding (?) issue with Fisher X-100

Discussion in 'Fisher' started by beatcomber, Jul 13, 2017.

  1. beatcomber

    beatcomber AK Member

    Messages:
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    Lexington, Massachusetts
    I have a '59 Fisher X-100 that has been rebuilt and is working fine and sounds excellent. However, it seems to be having what I believe is a grounding issue. When powered up, not only can I feel a slight electrical charge tingling on its metal surfaces, but I can also feel it on my turntable's arm tube and other metal surfaces as well. This was not an issue when I was using a Rega Brio-R (which has a grounded power cable).

    I suspect that the wiring in my old house has something to do with it too, because I have occasionally experienced this with a '70s Yamaha receiver elsewhere in my house.

    Some more details:

    • The Fisher, along with the rest of the components, is plugged into a Monster HTS5100 Power Center. (The Monster’s switched outlets are handy for preserving the Fisher’s power/volume knob.)

    • The Fisher has not been upgraded to a 3-prong cable.

    • When I was still using a powered subwoofer (also hooked up to the Monster), connected to the Fisher’s center channel jack, there was no tingling; the sub with its 3-prong power cable was apparently grounding the Fisher.

    • The room originally had an old-style 2-prong wall outlet, which I replaced with a 3-prong outlet with a ground wire connected internally to the metal casing inside. The ground light on the Monster is on, indicating that the outlet is in fact grounded.

    Any idea how to fix this? Would running a wire from the ground terminal on the back of the Monster to a chassis screw on the Fisher be a good place to start?
     
  2. gadget73

    gadget73 junk junkie Subscriber

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    Flip the power cord on the Fisher and see if it changes.

    Most older gear (and I'm not looking at the schematic, so spitballing this here) has a cap from one side of the line cord to chassis. Old non-polar plugs give you a 50/50 chance whether thats on the hot side or the neutral side. If you have this and have not replaced that cap with a modern one that won't fail shorted, I'd strongly suggest doing so.

    If it has a polarized cord, my guess is either its backwards inside the amp so the cap is on the hot side, or the outlet itself is wired backwards.

    A voltmeter from chassis to the cover screw on the outlet will confirm. ~120 vac means the cap is on the hot side, ~0 vac means its on neutral, ~60 vac means it has one from each side of the line and flipping the cord will do nothing.
     
  3. beatcomber

    beatcomber AK Member

    Messages:
    17,605
    Location:
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    Yup, tried that... no difference.

    Thanks! I sort of understand what you're saying - my tech knowledge is very rudimentary. I'll start by checking the outlet and chassis with a voltmeter.
     
  4. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    I think your problem is in the current turntable. Try reversing the Turntable cord in the Aux Plug or the Power strip. Is there a grounding wire from the turntable to the FISHER?? If so Remove it and test again. If you still get tingling remove the TT RCA's from the FISHER. This would remove the interconnections from the FISHER and Rule in or out the Turntable.

    HOWEVER, (cont'd below pic)........................


    ScreenHunter_85 Jul. 13 16.34.jpg

    No "Death CAP"in the X-100. If there was one it would be on the power cord side of the Power Transformer on one leg of the AC line to Ground. Disconnect the turntable from the FISHER completely and check the Fisher AGAIN. If you don't have the tingling then the problem is in the Turntable. If you feel so inclined, You can install one on the leg either before the switch(S-3) (to ground), or or before the aux pwr port (J-18) (to ground). You could install one to both sides as the plug is NOT Polarized therefore covering both sides. 01uf 300VAC X-Y Rated would work. But I don't think this would solve the current problem.

    Grounding the FISHER to the Power strip is Not a good idea. If the tingling is caused by the Turntable, you could have line voltage running thru the FISHER, and then to the strip.
     
  5. beatcomber

    beatcomber AK Member

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    The arm on my TD-124 is not connected to the turntable's chassis in any way (wooden armboard, arm not grounded to chassis), so I do not believe it could be creating the issue, right? But I will disconnect the various components one by one, and see if that reveals anything.

    Here are some more potential clues... this is the info that was provided in the seller's ad copy - the emphasis is mine:

    Electrically it is fully functional and has had some preventative work done to
    ensure a good long life. All of the electrolytic capacitors have been replaced with
    new 105C rated Nichicons, the coupling capacitors are Sprague Orange Drops,
    and a safety cap has been installed across the power cord. The rest of the caps
    are original. I also added 10 ohm cathode resistors so that output tube bias current
    can be measured individually. The power cord is a newer replacement as the
    original cord was in hazardous condition
     
  6. gadget73

    gadget73 junk junkie Subscriber

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    Flip it over and get a pic of the area where the power cord solders. That should tell us something.
     
  7. beatcomber

    beatcomber AK Member

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    You betcha. Will do this weekend!
     
  8. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    The TT motor itself could be causing the problem. The Jelco Arm and Denon cart IIRC should be grounded to the chassis and or to the FISHER. But I'll let some one with a TD-124 shout out.
     
  9. beatcomber

    beatcomber AK Member

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    Well, there are a few things I can say about that...

    • The Jelco is not grounded to the turntable's chassis, but it is grounded to my SUT.
    • The Fisher tingles even when the TD-124 is switched off.
    • Other amps I've used with the TD-124 (including a Fisher 400) didn't tingle.

    I really think it's the Fisher that's the problem.

    I'll take post some images of the chassis this weekend!
     
  10. beatcomber

    beatcomber AK Member

    Messages:
    17,605
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    OK, with the X-100 powered on, I have one-by-one disconnected and powered off all of the other components. The tingling did not stop.
     
  11. fred soop

    fred soop Super Member

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    In addition to the death cap, there is also capacitive coupling in the power transformer. The standard leakage test (which didn't exist when this stuff was built) is a 1500 ohm resistor in parallel with a 0.15 µF capacitor, this combination connected between chassis and ground. The equipment under test is to have no other connections except power. No antenna, no cables to other equipment, etc.

    The test is performed with all combinations consisting of both orientations of the wall plug and power on and off.

    Measured voltage across the RC network should not be more than 0.35 volts for any of the above combinations. If more than that, leakage is considered excessive.

    The line capacitors should be replaced with proper XY capacitors. X is line to line and Y is line to chassis.

    Digi-Key BC2379-ND, Vishay VY1472M63Y5UQ63V0, at 71 cents is X1Y1 rated (highest rating for XY capacitors) and is suitable for all X and Y applications.
     
  12. beatcomber

    beatcomber AK Member

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    I'm afraid that is all way over my head. :)
     
  13. Patrice B

    Patrice B AK Subscriber Subscriber

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    I guess, and correct me if I'm wrong, that he implies that the power transformer could be partially shorted?
     
  14. beatcomber

    beatcomber AK Member

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    Thank you. I can handle some simple soldering, but depending on what the images I'm about to post reveal (or don't reveal), I might need to bring this to a pro then...
     
  15. Patrice B

    Patrice B AK Subscriber Subscriber

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    When you touch the top of the power transformer, does it tingles?

    I had my Heathkit AA-100 doing this but the death cap... was dead!!
     
  16. beatcomber

    beatcomber AK Member

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    I have just disconnected the Fisher from everything (except a pair of speakers, to maintain a load) and plugged it straight into the wall. The tingling remains.

    See below...

    Yes, the tranny tingles a lot.


    IMG_0242.jpg IMG_0243.jpg IMG_0246.jpg IMG_0247.jpg
     
  17. beatcomber

    beatcomber AK Member

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    Here's the weird thing... with the meter set to ~200v, I got no reading. With the meter set to ~750, I got a reading of 240v! WTF? (FWIW, the power center indicates 120v more or less.)

    Am I not using the meter correctly? I've attached an image showing how I have the dials set.

    IMG_0248 (1).jpg
     
  18. beatcomber

    beatcomber AK Member

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    OK, this is messed up. Just for the heck of it, I moved the Fisher over to one of the original 1961 2-prong outlets on the other side of the room, and tried the voltmeter again. This time I got a reading of around 23v. User error?
     
  19. beatcomber

    beatcomber AK Member

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    FWIW, this meter was purchased in Australia, where the standard is 240v. But that should have nothing to do with what the meter shows, right?
     
  20. Patrice B

    Patrice B AK Subscriber Subscriber

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    You flipped the prong on the two sides and got 23v? Anyway, you're not supposed to have all this AC floating.
     

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