Basically these are whats called Universal Motors. If the Commutator rings are OK, than you can measure the DC Resistance of each coil by putting an Ohm meter on Opposite sides of that ring, checking one set of coils, than move each probe one pad to the right, to test the next coil. Continue till you have gone half way around. All Coils should measure Exactially the same Resistance.
A better test would be performed the same, but Measuring Inductance of each coil, also "Q" or a Ring Test. This would better determine a Shorted turn.
Even Better, Get a "Growler", Specifically made for testing Armatures.
Hope this helps...........Gary