It does prove frustrating.
Your best bet is someone who will show up to the next phonograph show
who can spell "electric motor". These things are not hard to fix
actually. The most likely problem is that the field is grounded and as
it is only a 2 wire device the case is also hot. It could also be the
resistor has seen better days. The field coils are wrapped with linen
strips and may or may not be then coated with tar. Either way when
running on AC the coils flex at a 60 cycle rate and over time the
wrapping fails and then the enamel on the wire wears through. This
usually occurs at one or more of the 4 corners of the pole shoe.
You can verify a field ground by connecting the motor to power and then
checking the frame to ground for voltage. Any reading of voltage
indicates a field ground. I have attached a drawing of a universal
motor, showing DC supply but the AC is identical, and you can see that
at least 2 grounds are required to bypass any field windings. This is
what you usually find when digging into these, multiple points of failure.
On 02/15/2013 10:07 PM, Vinyl Visions wrote:
Jim& Rich,Thanks for the info. My motor is definitely a Universal motor with carbon brushes.
The brushes are in excellent shape and the armature runs true. The main problem I'm having is
shorts, as opposed to opens. The motor runs until a load is applied, then you can basically shut
it down with your fingers. The "REAL" problem that I have had is due to our
geographical location - North Carolina. There are some very good motor shops, but they won't mess
with a small problem motor that doesn't generate any return business. If you find a mom& pop
operation, they work whenever they get around to it... I left it with one place and the owner
promised he would get to it in a week - two months later I went back to check and it was still
sitting on his desk in the same place I left it. Another said he could rewind it, then quit his
job. Another guy sent it to Michigan to someplace that was willing to work on it, but wanted $900
with no guarantees that they could fix it. As far a
s
electrical engineers go, 99.9% of the population probably don't know what electrical engineers do
for a living and they are not in abundance around here, except at the nuclear power plant. The guy
who works on your motor may or may not have graduated high school and knows how to fix one or two
common motors that are used commercially - give him a challenge and it ends right there. I am tired
of being asked by people in motor shops - "What are you going to use it for?" or
"What's wrong with it?" If I knew what was wrong and how to fix it, I wouldn't be asking
them. What difference does it make what I'm going to use it for? I just want it to run... AND if I
did explain that I wanted to use it in a lamp phonograph... you get the picture. Do I sound
stressed?
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