Smoke From PSU Socket

Tony Duell ard at
Mon Mar 28 14:09:40 CDT 2011

> > If a properly-funcitoning DELNI draws anyhting like 10A from the mains, I
> > will eat one :-). I am sure it would be fine.
> I am absolutely sure it will be fine in this respect.

I have now dione what I should have done ages ago amnd looked at the 
DELNI printset on bitsavers (under dec/ethernet IIRC) [1]. I find that 
the printset is always the best manual to look at first :-)

[1] As you all know by now, looking at on-line documentation is rather 
more work for me than for most people, which is why I didn't instnatly 
look at bitsavcers to see if there was anything useful.

Anyway, I was somewhat suprised by the PSU. It's not an SMPSU. At least 
one of the regulators looks to be a switching type,, but the power supply 
starts with a mains transformer (running at 50Hz or 60Hz). The primary 
windings of that transformer go to the nromal series/parallel switch and 
then to the mains input. Oh yes, there's a fuse in series with the live wire.

Now, 10A, even at 110V is over 1kW. a 1kW (more correctly 1kVA) 
trransformer is a big lump of iron. I doubt one would fit in the DELNI 
case. So I am sure a 10A filter will be fine.

When you replace it, make sure that the wire that goes to one end of the 
fuseholder goes to the live output tag on the filter. It's very clear 
from the schematic.

[Modifying the case]

> > And if it isn';t, a file will take care of the problem :-)
> Hmm... I definitely don't want to do that. From the pictures on the

Well, agreed, I'd rather mont have to do it, but it's better to slightly 
enlarge the hole than have a non-working device, isn't it?

> Schaffner site it *looks* like it will fit the cutout just fine. I'd like to

I think it will, these things come in fairly standard sizes. 

Admittedly it was just an IEC320 plug, not one with a built-in filter, 
but I found a generic plug from the local electroncis shop was a perfect 
fit as a replacement for a broken one in an HP9820 calcluator made over 
25 years earlier. No cutting, filing or drilling needed.

> measure the old one, but I can't get the damn thing out at the moment. One
> of the nuts holding it in is in an awkward position, annoyingly, I don't
> have the 1/4" spanner you need to undo the nut and pliers won't reach. I am
> going to have to find a suitable spanner first.

SInce when have pliers been a substitue for a spanner??? Darn it, I don't 
even like using adjustable spanners if I can avoid it.

Incidentally, I find I need 3 sets of spanners to work on classic 
computer stuff : 

Inch size (to fit USA built stuff mostly). And I need odd sizes like 
11/32" sometimes.

Metric sizes (needed on just about anything modern-ish, and everything 

BA sizes. BA is a strange thread used mostly on older British stuff. You 
need BA spanners to work on Creed teleprinters, for example.

AAnd yes, open-end, ring (box end?) and nutdrivers are all useful. 


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