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The curious case of the AC voltage detected on my EQ6 Mount/Tripod


dave_tucker

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I've been rebuilding my EQ6... and when I put everything back together I was surprised when I felt a little electric vibration on the Dec Scale... and again on the counterweight shaft.

Being curious as I am, my multimeter has a NCV function... If I point it at any part of the mount or tripod when it's plugged in, it detects voltage 🤯
Now, it's only supposed to alarm when there is > 90VAC...

I was expecting it to be a grounding issue, but if I take a measurement from the mount or tripod to ground, I get a reading between 25VAC at basically 0.01mA🤔

I'm at a bit of a loss as to where the issue could be coming from.... any advice or suggestions appreciated.
 

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Most if not all switch mode power supplies these days have no earth so the 0V output pin will be at around 70V or more, I have never understood why this is deemed safe by regulations. The best fix is to run a "safety" earth directly to the mount and any other metal parts.

Alan

Edited by Alien 13
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Switch-mode supplies contain 2 capacitors, one from one mains terminal to output (positive) and likewise from the other mains terminal to output (negative). The idea is they feed interference away into the mains supply, reducing RF noise. The capacitors are low value, meaning there is no electrocution risk (see below though).

There are three consequences, one being that the output "floats" at half mains voltage. Another is that a capacitor failure can place mains voltage on the output - which is why a "fail open-circuit" class of capacitor is supposed to be used. These cost more, so you may find unsafe substitutes in dubious-source gear. The  third consequence is in connecting other gear, with an earth and sensitive inputs, to the powered-up gear. It can and does destroy sensitive electronic input circuits as the capacitors discharge the "floating" voltage. Connect all gear first then apply mains, to avoid that risk. Usually not mentioned in the manual!

Edited by wulfrun
clarity
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