TM 10-3930-653-14&P (0.008 in) from commutator surface, commutator (armature) should be turned on a  lathe,  so  that  the  out- of-roundness is less than 0 05 mm (0.0020 in) insulating mica should also be undercut so that the depth of it is 0.5 to 0.8 mm (0.020 to 0 31 in). Wear  limit  of  the  commutator  diameter  is,  2  mm (0.08 in).  It the commutator is beyond repair, replace. Note It is recommended to replace commutator as an assembly if worn or damaged. Fig. 4-162.  Inspecting Commutator for Out-of-Roundness Fig. 4-163.  Undercutting Insulating Mica (3) Inspect  soldered  connection  of  armature  lead  and commutator.  If loose connection is found, solder it using rosing flux. (4)Armature test for ground Using   a   circuit   tester,   place   one   test   probe   onto armature shaft and other onto each commutator bar. If    the    tester    shows    continuity,    the    armature    is grounded and must be replaced Fig. 4-164.  Armature Test for Ground (5) Check   armature   for   short   by   placing   it   on   the armature   tester   (growler)   with   a   piece   of   iron   over armature  core,  rotating  armature.    If  the  plate  vibrates, armature is shorted Fig. 4-165.  Armature Test for Short-Circuit (6) Check  armature  for  continuity  by  placing  probes  of tester on two segments side by side.  It tester shows no continuity, circuit is open 4-98