It's time to restore the 11/45.

tony duell ard at
Thu Feb 5 00:08:36 CST 2015

> Interesting. I bought an 11/45 about a year ago which I still need to look
> at. I have been wondering about the PSU in particular and how to test it
> before attempting to power the machine.
> I am guessing I could test the transformer part fairly easily on its own,
> without any of the bricks, and without loading it, just checking that the
> outputs are all 30VAC. I haven't looked yet, but is it just a big
> transformer?

The front section of the PSU is the big mains transformer and a PCB 
with the +15V supply, ACLO, DCLO, LTC circuitry on it. You can 
disconnect this and test the transformer on its own. For 230V 
mains the 115V fans (throught the PSU and CPU) run off the
transformer primary as an autotransformer.

> Presumably I can then test each brick individually, with a suitable dummy
> load, and to make testing on the bench simpler, I could feed it 30VAC from

You can. The pinouts are not the same in all cases (but are in the printset and
IIRC on the bricks themselves). The -15V brick needs a +15V DC input as well, 
but that is at minimal current and not hard to provide.

> my Variac rather than have to hulk the huge transformer part around.

Bad idea. A plain Variac does not provide isolation from the mains so you 
are actually now working on mains-connected circuitry (read : dangerous and
you can't clip a 'scope on it). The input voltage is not that cricitcal (I think it can
be as low as 20V) and doesn't have to be AC. I think 30V DC from a bench supply
would work.

One very useful thing I made up was a cable with an 8 pin mate-n-lock
connector on each end. I use it to run the bricks outside the PSU chassis 
-- although they lose the cooling fan blast, they do not overheat for short
periods on dummy load (they are switching regulators anyway, so they run
quite cool). I then sit the brick I am testing on top of the CPU (pulled out 
from the rack). Of course the problem is finding the connectors.

> Is there anything bad about my plan? (There must be, it is too simple :-))

See above...


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