False alarm, I think. (Beyonwiz wired incorrectly?)

[matthewc]

EDIT: I tried switching around the terminals and it didn't make a difference. I think what I'm seeing is just a consequence of the unearthed secondary side of the transformer tending to track the sinusoidal input waveform, and probably not a real danger. Consider this a false alarm.


While tinkering around with an oscilloscope I noticed something potentially dangerous: my Beyonwiz seems to have its ground plane (including chassis) biased to active rather than neutral.

It seems that the white plug from the mains may be wired the wrong way: blue is connected to the terminal marked L and brown is connected to the terminal marked N. [Edited, thanks]

If anyone else happens to have their BW open, or has a multimeter handy to check the metal part of the chassis, could you check if yours has the same problem or if it's just a rare assembly error?

[Htnut]

Nothing wrong with the BW. Brown should be L (live) and blue N.

[matthewc]

Yep sorry, I confused myself when writing the post, I meant it the other way round. Blue is connected to live and brown to neutral in my BW. When looking at the AC power plug as you put it in the socket, neutral is on the left and live on the right (tracing from the contacts labelled on the power supply), which I'm pretty sure is backwards.

[peteru]

If I recall correctly, the Beyonwiz is not grounded, just double insulated. The only path to common ground would be thorough the antenna connection and only if your system is grounded (in multi-residential dwelling it has to be grounded by law)

So, you'll always get floating ground, sometime enough to actually get zapped when you touch things. There's a gas outlet near my Beyonwiz, which is grounded. I touched a metal part of the gas outlet it while I was handling the Beyonwiz and got a hefty zap. Enough for a spark and to make me jump.

The Topfield TF5000PVRt used to exhibit similar behaviour. It would give you quite a buzz and people have been know to fry USB ports on their PCs.

I would have preferred it if the Beyonwiz had a grounded chassis with a ground isolate switch, like my subwoofer.

[prl]

Anyway, neutral shouldn't be connected to the case. That would just need one wiring error anywhere in the path to the device to give you a BW that could be tricky to pick up

Have you tested resistance from neutral to case?

[matthewc]

Yes you're right, neither neutral or active is actually connected to the case. The DC resistance is healthily high.

The AC coupling is what I was looking at, which I've subjectively experienced as my BW feeling 'wooly'. My initial worry was that it might have related to the backwards wiring on the input, but now that I think of it, I doubt that the power supply does anything with the input other than passing it through a transformer - and given that the secondary side of the transformer is not earthed, it seems not unexpected that the floating voltages follow the sinusoidal input.

I doubt that it poses a serious danger, so my apologies for being alarmist.

[tonymy01]

In switch mode supplies you often find ceramic caps tieing the high voltage input to the chassis, presumably for noise isolation, so these can store up enough charge to zap you a tiny bit also.

[DaveR]

In switch mode supplies you often find ceramic caps tieing the high voltage input to the chassis, presumably for noise isolation, so these can store up enough charge to zap you a tiny bit also.

If I recall correctly, the Beyonwiz is not grounded, just double insulated. The only path to common ground would be thorough the antenna connection and only if your system is grounded (in multi-residential dwelling it has to be grounded by law)

So, you'll always get floating ground, sometime enough to actually get zapped when you touch things. There's a gas outlet near my Beyonwiz, which is grounded. I touched a metal part of the gas outlet it while I was handling the Beyonwiz and got a hefty zap. Enough for a spark and to make me jump.

The Topfield TF5000PVRt used to exhibit similar behaviour. It would give you quite a buzz and people have been know to fry USB ports on their PCs.

Could this pose any danger to someone with a pacemaker
I have been zapped by PVRs on occasion. I've even measured it at around 100v AC (at a very small current level).

[peteru]

Could this pose any danger to someone with a pacemaker

No idea, but this is probably one experiment I would not be conducting.