4 Feb
2015
4 Feb
'15
3:52 p.m.
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>
wrote:
there is
a
-----Original
Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
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.
they are not
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 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
regulator
'bricks' that, if it fails, causes ACLO
and DCLO to pulse at power line
frequency
(or probsbly twice that frequency). This really
gives the 11/45
headaches,
the
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
would
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
subject.
> Datapoint: I didn't mess at all with
power supply / caps on my 11/34,
which
> 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
11/45
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 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
lethal
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
transformer?
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 :-))
Regards
Rob