You were right, it is switching noise. As you said, I was zoomed in too far, I hadn't paid proper attention! The actual ripple is about 50mV peak to peak.
https://rjarratt.files.wordpress.com/2022/03/pin-1-5v-averaged-ripple.jpg Regards Rob > -----Original Message----- > From: cctalk <cctalk-boun...@classiccmp.org> On Behalf Of Matt Burke via > cctalk > Sent: 29 March 2022 01:31 > To: cctalk@classiccmp.org > Subject: Re: PDP 11/24 - A Step Backwards > > On 28/03/2022 23:22, Rob Jarratt via cctalk wrote: > > Its 600mV, but it is more of a spike than a ripple. Here is a trace: > > https://rjarratt.files.wordpress.com/2022/03/pin-1-5v-ripple.jpg > > > > I think that's just switching noise. You appear to be zoomed in on the point > where the main switching transistor is turning back on. Here is a trace from > an H7100 power supply (connected to a 70A dummy load) for > comparison: > > http://www.9track.net/posts/h7100_trace.png > > If you turn on averaging mode on the oscilloscope (acquire menu) then that > should filter our some of the noise and you will be able to see the actual > ripple a bit better. It should be noted though that a differential probe is > required for accurate ripple and noise measurements. > > Regards, > > Matt