MicroVAX 3100 Model 95 Ripple

[Jon Elson]

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-psu-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