MicroVAX 3100 Model 95 Ripple

[Rob Jarratt]

The spikes are 400mV. The probes are set to x10 and the scope is set for
them to be x10.

Regards

Rob

> -----Original Message-----
> From: Jon Elson <elson at pico-systems.com>
> Sent: 09 May 2020 17:45
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Subject: Re: MicroVAX 3100 Model 95 Ripple
> 
> On 05/09/2020 11:32 AM, Rob Jarratt via cctalk wrote:
> > Hello,
> >
> >
> >
> > I have recently been trying to improve the ripple on the output of my
> > MicroVAX 3100 Model 95 PSU because occasionally it would fry a memory
> > module. I replaced a bunch of capacitors, some of which had started to
leak.
> > However, the ripple does not seem much better. There is a scope trace
here:
> >
> >
> >
> > https://rjarratt.files.wordpress.com/2020/05/microvax-3100-model-95-ps
> > u-ripp
> > le-after-re-capping.png
> >
> >
> >
> > Ch1 is the 12V output and Ch2 is the 5V output. I had an old RD53
> > connected as a dummy load. It is possible that the memory was breaking
> > because of occasional spikes that are worse, but I don't know. Does that
seem
> OK?
> >
> >
> These spikes are very likely not real, but a result of probe ground
impedance.
> There likely ARE some spikes and ripple, but not to the extent of the
giant,
> sharp vertical spikes.  If you are using a X10 probe, does the 200 mV /
div on
> the scope trace reflect that attenuation?
> 
> In other words, are the spikes 400 mV or 4 V?
> 
> Jon