[sdiy] Casio CZ-3000 with mains to chassis fault

Ingo Debus igg.debus at gmail.com
Wed Sep 1 17:05:47 CEST 2021


> Am 31.08.2021 um 06:59 schrieb cheater cheater via Synth-diy <synth-diy at synth-diy.org>:
> 
> Hmm, I mean, I can see that, but this hurt way more than the mains
> shock I got a couple years back. Makes sense given that static is
> higher voltage

It's not the voltage that matters when you get zapped, it’s the current. Mains voltage can kill a person or the shock can be so light that it even doesn’t get noticed.

There are two kinds of EMI suppression capacitors: a X cap is connected between the prongs of the mains plug and Y caps are connected between one prong and the chassis. A X capacitor can have several 100 nF, so you can get a good zap when touching both prongs when the device was recently unplugged (and turned off, otherwise the X cap quickly discharges into the device). There should be a bleeder resistor that discharges the X cap in a couple of minutes.
Y capacitors are much smaller, so I think it’s unlikely to get a strong zap from them.

I remember unboxing a new computer (styrofoam box, plastic bags, all that stuff) at work in a professional ESD-safe environment. I still got zapped… It seems to me more likely that you got zapped by ESD than by a capacitor previously charged from mains voltage.

Ingo


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