TM   10-3930-638-24&P 3-13.  STARTER  AND  SOLENOID  REPAIR  (cont) STEP LOCATION ITEM ACTION REMARKS TESTING  (cont) Rotate armature slowly one or more revo- lutions. If the armature is shorted, the steel blade will vibrate. Turn power off . Position armature in growler, as shown. Turn power on c. Armature (10) Test commutator Follow directions supplied with growler bars and test commutator bars for abnormal readings.  Abnormal  readings  will  indi- cate a short, open or poor connection. If  testing  indicates  commutator  is grounded,  the  armature  is  shorted  or commutator  readings  indicate  a  short, or an open or poor connection, replace armature 17 Disconnect field coil ground connection. Use test lamp. Connect one test probe of the test lamp to the connector (2) and the other probe to the frame (7). If the test lamp lights, the field coils (52) are grounded. If coils are grounded, remove and replace coils. Touch test probes to each end of the field coil windings. If the test lamp does not light, the field coils are open. If coils are open, replace coil assembly (52) REASSEMBLY 18 Field  frame a. Field coil assembly Assemble  and If  removed (7) (52) position b. Four pole shoes Position (51) c. Eight screws (50) Install d. Grommet (49) Install If  removed Test Field  coil  assembly (52) 3-109