It's time to restore the 11/45.

Robert Jarratt robert.jarratt at
Wed Feb 4 15:33:16 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of tony
> Sent: 04 February 2015 19:03
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: It's time to restore the 11/45.
> >
> > 4) This would also be a good time to broach the subject of whether or
> > not the capacitors need special love, or if that just adds more risk
> > of destroying something.  Those familiar, please chime in as the
> > archive is
> My 11/45 which was working last year until I moved house (I haven't
> reassembled it yet, or attempted to undo any damage caused by the movers)
> still has all the original capacitors in the PSU.
> I find this 'witch hunt' of capacitors curious. Yes, they do fail, but
they are not
> the only, or even most comon, thing to so so.
> BUT!
> There is a capacitor in the front section of the H742 PSU -- not in the
> 'bricks' that, if it fails, causes ACLO and DCLO to pulse at power line
> (or probsbly twice that frequency). This really gives the 11/45 headaches,
> microcode keeps on trying to handle the power failure and won't let you do
> anything else. So while I would not replace any capacitors 'on spec' I
> check that the ACLO and DCLO lines are doing the right things.
> > currently missing so I can't refer to the recent threads on this
> > Datapoint: I didn't mess at all with power supply / caps on my 11/34,
> > was stored right beside the '45 for the same timespan and it's running
> > great now.  Datapoint 2: with my amateur electronics skills / status,
> > there's admittedly some risk just having me poking around in there,
> > "learning" things :-\   Plus, I'm afraid of death from esoteric high
> > voltages that I hear are present in these old power supplies.  Is the
> > one of them?  In a nutshell, this analog / power stuff is FAR FROM my
> The 11/45 PSU is fairly friendly. There is, of course, mains inside, but
there is a
> big
> (looks to be about 1000VA) transformer in the front section, giving out
lots of
> 30V AC outputs. The regulator bricks are fed from 30V, so there are no
> voltages
> inside. But given that it's 30V at 10's of amps, there is enough power
there to
> do damage.
> I have had transistors blown off the PCB when I had a nasty failure in one
of the
> regulator
> units.

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

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

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



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