Microvax II 'primer'?

Jules Richardson jules.richardson99 at gmail.com
Mon Jan 22 07:43:33 CST 2018

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).

I see on the output rating label that it lists connection points for 
different outputs, so maybe I just need to slap a couple of suitable 
resistors onto the +5V and +12V outputs so that they draw an amp or so, and 
see how it goes.

> Once you have the machine up and running...

Lets not get ahead of ourselves ;-)

> I am not sure if 4MB is enough to do that though.

Hmm, one of the things that I'm clueless about right now is how the bus 
evolved over the years - I've still got a pile of Q-bus boards which I 
saved from a recycler last year, and I know there's a 4MB board (made by 
Clearpoint, if I remember right) among them. But if that's designed for 
earlier PDP hardware then it's possibly no use whatsoever in a Vax world...



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