Robert Berta

The OP said he is getting tingling when touching anything on the mount, pier, CP 4 box, etc. that is NOT normal and could be an issue. I am a retired electrical engineer that worked many years for an electric utility in California. 

I assume you are running AC to a regulated  DC power supply for everything.

First thing I would do....get a phase check device from your hardware store to confirm if your house is wired correctly. This is an inexpensive little block that has the two flat prongs and the round prong like a standard electric plug.  The device will usually have three LEDs on it that will help determine if you have the house circuit wired correctly. You would be amazed at how many houses aren't wired correctly.

A little electrical class first. A standard  plug will have two flat blades one of which is wider than the other. The smaller blade is the hot leg, the larger flat blade is the ground. The round lug  is the case ground and should not be grounded and it definitely is NOT a ground as many think. Its purpose is to connect the case of your device to other device cases so they all have the same "electrical potential". This means that if you touch two different devices you won't get zapped. Often people will find the two flat blades are reversed because the contractor wired the outlet wrong.....or someone will use an old style two blade plug that has same size blades on each side.and plug in upside down. Sometimes people have very old house wiring that only has the two same size flat blades and no round lug.....and they want to plug a modern two blade/round lug device in. They get an adapter from the hardware store that is designed for that purpose. There is a pig tail or sheet metal piece that acts as the round lug when it is screwed into the center retaining screw on a wall plate. If the adapter is plugged in backwards or the case ground is not connected you have a problem.

If you touch the metal of a a device and get a tingle that is an indicator of this issue. You are standing on the ground and the path of least resistance is through your body. When I was young my families refrigerator outlet was wired backward which meant if one of us leaned against the metal door and someone else leaned against the metal edge around our kitchen sink and you touched each other you got a mild shock. Of course being kids we delighted in zapping our family members and friends ;-) That came to an end when I became an engineer and figured it all out. Kind of ruined my brother and sisters fun though ;-) 

This may not be the final cause of your mystery bug....but something to check.  I would also take Roland's recommendation to heart. Run everything from a 12 volt battery and see if the problem goes away. You won't get a tingle from 12 volt equipment. But you could get zapped if you are using a 12volt DC to 120 volt AC inverter in the field for some reason. Those are notorious for bad grounds since they don't have one normally and can cause all kinds of gremlins.

---In ap-gto@..., <J.Zeglinski@...> wrote :

    Would it help isolate the problem source, if Martin would unplug each of the servo motor cables, one at a time?
     A vibration might potentially be caused by a stuck servo motor, a fallen screw/part inside the motor box, or its rubbing internally against its case/mount. Perhaps a wonky servo shaft. Might also explain the electrical tingle he feels from touching the CP4, if the short was caused by a motor power attachment,  mechanical failure, leading to a DC short to the case and mount. Otherwise, if there is still mount vibration when either motor’s power is isolated, then as you suggested, it may likely be a power source leak going to both motors via the CP4, causing the mount to conduct the vibration.
    Pure conjecture on my part, but I would eliminate each motor’s power feed, in turn, since a “mechanical vibration” can only emanate from a mechanical source and there are just these two,  on the mount. Besides changing the DC power supply, I suggest completely disconnecting all accessories on the telescope – just power the mount directly, in case a current leak is coming to the CP4 via some other device/accessory.

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