Punch solenoid coil problem on old Flexowriter

Gary Oliver go at aerodesic.com
Tue Oct 13 12:09:48 CDT 2015

I'm in the process of refurbishing an old model SPD Flexowriter (from 
the 1950s.)  When I
placed it in storage, all worked ok.  The storage room was dry (though 
not heated or cooled)
and there were no mice or other vermin involved in it's repose. However, 
upon starting it
back up (and lubing every moving part beforehand) I discovered the punch 
wasn't firing
"on all cylinders."

After disassembling the punch solenoid block, I discovered two of the 
coils were now open
(corresponding to the two missing positions) but also, two coils had 
apparently shorted
somewhere and changed value.  From a nominal 850 ohms, the two were now 
about 150 and
500 ohms.

I have a lot of old gear with relays (similar to these driver coils) and 
I've *never* had a problem
with an open relay coil (that wasn't caused by obvious damage.)  Is this 
a problem any of you
have experienced and if so, have you ever discovered the root cause?  I 
presume it is some
corrosion, but the open coils were open near the middle of the winding 
(#41 AWG wire with
about 11000 turns.)  The breaks were NOT at the junction of the #41 and 
the sturdier wire
that connects to the terminal block.

Also, question 2: the Flexowriter parts list shows two different coils 
(both 850 ohms) used in this
assembly.  Four of one and four of another.  I'm presuming these are 
magnetically polarized
so that half are North-up and half are North-down in order to not have 
truly strange things
happen all 8 are firing and you get so much magnetism that some 
armatures are repulsed
rather than pulled, but I don't find that mentioned in the manual. I'm 
planning an experiment
with a hall-effect sensor to verify.  So far my failures have all been 
one type so I don't have any
to visually examine while I'm unwinding them.  The Flexo parts differ 
only in their part
number - no other visible differences are seen.

I am rebuilding the coils as I have an ample supply of #41 but I want to 
know if I need
this 'normal/reverse' polarity thing if it exists.  So far, I've rewound 
one coil with a match
in wire direction to the one it replaced and it seems to be ok.


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