PDP 11/24 - A Step Backwards

[Rob Jarratt]

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-bounces at classiccmp.org> On Behalf Of Matt Burke via
> cctalk
> Sent: 29 March 2022 01:31
> To: cctalk at 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