It's time to restore the 11/45.
jacob.ritorto at gmail.com
Wed Feb 4 17:52:45 CST 2015
My NASA EE buddy recommended working up an appropriate load from regular
household lightbulbs. They won't light, naturally, but you can dial in
your load by simply choosing certain wattages and doing the math.
On Wed, Feb 4, 2015 at 4:33 PM, Robert Jarratt <robert.jarratt at ntlworld.com>
> > -----Original Message-----
> > From: cctalk [mailto:cctalk-bounces at classiccmp.org] 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
> > microcode keeps on trying to handle the power failure and won't let you
> > 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
> 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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