Sounds like the telehone protective device at the
entry to your premises shares the same earth 'ground'
with your AC mains.

Connecting the scope 'ground' to one side of the
bridge forced current into the 'protective'
ground, but, the so-called 'ground' wasn't really
ground BUT did feed back into the phone system
through the 'protective' device (composed of
varistors, they used to be made of gas-filled
arc-suppression 'tubes' - like neon bulbs that
fire at 60 volts or so ...)


Jim

----- Original Message -----
From: "Edson Brusque" <ebrusque@TERRA.COM.BR>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, February 14, 2002 5:49 AM
Subject: Re: [EE]: bad oscilloscope?


> Hello Picple,
>
> > Yes, i plug the scope in the main, switched on, self test passed ok,
then
> > attach the probe to channel 1, the clip in the probe to one wire of ac
> line
> > (not shure if neutral or live), and the pin of the probe to the other
wire
> > of ac..-> spark!.
>
>     hehehe, I have a very weird experience times ago. I was buildin
> something on a prototype wireboard, with the mains AC going thru 4 diodes
in
> a bridge rectifier configuration and something (mostly resistors zener and
> caps, I was building a no-trafo PSU). So I connected the scope probe clip
on
> circuit earch (that is constantly changing phase/neutral because of the
> bridge rectifier) and ALL the phones on the house started ringing! It take
> me some time to figure that one thing had to do with the other and
> disconnect the clip. I waited some seconds with a bit '?' inside my head
and
> then curiosity made me connect the clip again...
> RRRIIIIIIIIIIIINNNNNGGGGGGG! I disconnected and decided not to think about
> it.
>
>     Ohhh, I burned two modems when doing this.
>
>     Best regards,
>
>     Brusque
>
> -----------------------------------
> Edson Brusque
> Research and Development
> C.I.Tronics Lighting Designers Ltda
> Blumenau  -  SC  -  Brazil
> www.citronics.com.br
> Say NO to HTML mail
> -----------------------------------
>

>

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