[GreenKeys] WU Modeal 2-A "Iron Horse" doesn't strike

[Ethan Blanton]

Greetings all,

I have a Western Union Model 2-A "Iron Horse" perforator that I'm
trying to debug.  It is an extremely simple device, and it seems to
check out, so I'm a bit stuck.  I'm hoping one of you has some advice!

The symptom is that the solenoid does not strike when a key is
pressed.  If I move the punch mechanism out of the way (which takes
several pounds of force, and may be too heavy, but I don't think
that's the fundamental issue), the solenoid does move, but with no
more than a couple of ounces of force.  Certainly not enough to drive
a punch through a paper tape, even *without* the mass of the punch
mechanism or the return spring.

The individual coils in the solenoid seem OK (they each measure about
78 ohms, and are 82 ohms nominal according to the manual) and the
solenoid windings are properly in series and receive full line voltage
when a key is pressed.  The impedance across the line cord with a key
pressed is almost exactly the impedance of the solenoid coils, so I
don't believe they're being under-currented.

This unit is *extremely* simple (it doesn't even have the repeating
mechanism shown in the manual), and I have removed all unnecessary
devices from the harness (e.g., the EOL lamp) for testing.  The
devices remaining in the circuit are the keyboard contact that
triggers the solenoid (nominal resistance when closed) and a 100 ohm
wire wound resistor (checks at almost exactly 100 ohms) in series with
a 1 uF (oil can?) capacitor that is in parallel with the solenoid and
appears to be line filter of some sort.  The capacitor is the only
part that seems suspicious, and I tried replacing it with a 1 uF 400 V
capacitor out of some film capacitors in the junk bin, but this had no
effect (I didn't see how it would, but ...).

Any ideas?  Is the solenoid bad?  I don't see how the coils could be a
problem, really (they look fine, they have nominal resistance, they
aren't getting warm, etc.).  Something in the armature?  I haven't
disassembled it (I think I see how, but I can't see everything, so
...), perhaps it's missing some iron?

Thanks,
Ethan