Microvax II 'primer'?

Jon Elson elson at pico-systems.com
Mon Jan 22 10:49:19 CST 2018

On 01/22/2018 07:43 AM, Jules Richardson via cctalk wrote:
> On 01/21/2018 04:04 PM, Rob Jarratt wrote:
>> You might find that the filter capacitor goes up in smoke 
>> soon after you
>> connect the PSU to the mains, even without powering it on.
> Yes, Adrian Graham mentioned that (via FB), too. I seem to 
> have extremely good luck with the RF filter caps, unlike 
> other people, but I'm always prepared for the cloud of 
> smoke :-)
>> Otherwise it is certainly wise to check the PSU visually 
>> for any obviously
>> failed electrolytics. If  you have one of the DEC load 
>> boards you could
>> connect the PSU to that as a dummy load. I don't think 
>> there is much in the
>> way of dependency on the CPU to run the PSU.
> At this stage I've got no idea if it's a SMPSU or a linear 
> (I've not popped the panel off)... I suppose if it's 
> linear then it perhaps doesn't even need a load to do its 
> thing. If it's a switcher then I expect it'll at least 
> need something on +5V, and maybe +12V too (unless it has 
> built-in load resistors to keep the regulation happy, as 
> designs occasionally do).
All VAX and uVAX main power supplies are switching types.  
If you see an electrolytic cap in there with a 200+ V 
rating, that's a certain giveaway of a switching supply.


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