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.
TIA,
Gary
