Hello Folks,
Thanks for all thoses interestings comments.
As Ive reconnected the ground, and turned power ON : no differential
main shut down occur, even when my finger
played with chassis parts. I also mesured voltage between ground and
chassis : close to zero -- few mV-..
The idea to use the same wall socket to avoid ground loop is fine.
Question : sometime when troubleshooting radios, I use a ground lead
between scope and radio to avoid using probe's aligator clip.
What do you think about ? can I introduce false mesurements ?
Regards
Alain
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Le 15.08.2018 ¨¤ 20:40, Richard Knoppow a ¨¦crit?:
??? A hot chassis can also be caused by RF filter capacitors connected
from each side of the line to the chassis. I would be much more
suspicious of these if they exist in the 453 than of the electrostatic
shield in the power transformer. If there are such caps in the 453
lift them to see if the voltage on the chassis disappears. You might
want to replace them. There are special capacitors for this service
which fail open so they don't connect the line directly to the chassis.
??? The voltage on the chassis will depend on the amount of
capacitance and the impedance of the measuring device.
??? You can always generate a long argument by discussing the
differences between lightening protection grounds, power line safety
grounds and grounds to eliminate common impedances in AF and RF circuits.
On 8/15/2018 1:52 AM, Craig Sawyers wrote:
That would be typical if the chassis is ungrounded. Capacitance
between the primary and shield (which
is connected to the chassis) in the mains transformer will cause
this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous
thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope
safe first.
Craig
