On 9/3/25 11:18, Rob Jarratt wrote:
-----Original Message-----
From: Jon Elson via cctalk <[email protected]>
Sent: 03 September 2025 15:39
To: [email protected]
Cc: Jon Elson <[email protected]>
Subject: [cctalk] Re: Repairing an Olivetti M24 PSU
Those are not real. They are conducted interference from the switching
supply getting into the scope preamp via the ground lead.
I have seen this MANY times, ignore it.
Jon
Thanks Jon, obviously I don't have enough experience to know this. How can I
recognise this in the future?
Switching power supplies generally radiate a ton of
electrical fields at their switching frequency. If you see
insanely high frequencies in these measurements, you can
usually assume they are radiated interference. You can also
turn on the scope's bandwidth filter. I did see REAL ripple
in one of the traces, there were long straight lines with
slight tilt between the noise pulses, those are the real ripple.
Improving the ground connection at the scope probe also
helps. The power supply injects currents into the ground
terminal due to capacitance between output transformer
windings, and these current flowing in the probe's ground
braid contaminates the measurement. Possibly running a HEAVY
copper braid between the scope's ground terminal and the
power supply ground will reduce the effect.
Jon
