[GreenKeys] UPDATE- shockingly basic question - Teletype Model 33 ASR

[Andy KN4UCL]

I have a cheap little Hantek DSO5102P which is grounded.  So assuming I
managed to correctly hook up the earth crocodile clip from my scope to the
teletype ground (presumably any part of the chassis) I should be ok to have
a little probe around, yeah?

On Thu, Feb 11, 2021 at 6:09 PM Jim Cooper <jim.w2jc at gmail.com> wrote:

> On 11 Feb 2021 at 12:29, Nick England wrote:
>
> > *Across* the resistor???? Do you
> > mean scope probe to one side and
> > ground clip to the other?
> >
> > Careful! If part of the loop is
> > grounded, and you hook up the scope
> > ground to the wrong spot, you can
> > short out the power supply. Sparks
> > sparking! Fuses fusing! Transistors
> > blowing quickly to protect the fuse!
>
> Well, yes ...  but never a good idea to
> stick an instrument that's not 'floating'
> into any circuit.
>
> > I am a M33 ignoramous, but isn´t
> > there a selector magnet driver?
> > That´s where Russ was talking about
> > ripple, not a signal loop.
>
> Well, the complaint is bad characters
> being printed ...  scoping across the
> selector magnet should give the same
> waveform as scoping across the current
> limit resistor, except you might also see
> spikes from the inductance ...   and wouldn't
> your caveat about ground hold for clipping
> on the SM as well ?
>
> > I could be reading this all wrong.
> > Nick
>
> or maybe I am ...
>
> >
> > On Thu, Feb 11, 2021 at 11:55 AM Jim Cooper <jim.w2jc at gmail.com>
> > wrote:
> >
> > > On 11 Feb 2021 at 11:20, Andy KN4UCL wrote:
> > >
> > > > *Well that makes sense. Looking at
> > > > my ring binder (Tech bulletin 310B
> > > > Vol2) I have a power supply circuit
> > > > diagram, but I am not sure where I
> > > > would physically plug in my highly
> > > > underused budget Hantek scope...*
> > >
> > > If your scope can handle the voltage,
> > > one simple place to put the scope is
> > > across the current limiting resistor
> > > in the loop (usually about a 2k resistor).
> > >
> > > You will then see the square pattern of
> > > the character code.
> > >
> > > w2jc
> > >
> > >
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