GMC T Series 1994 Repair Manual page 583

Figure 13—Testing the Armature for Grounds
Figure 14— Checking the Field Coils for Grounds
(SD-300)
6. Armature for grounds by using a test lamp (figure
13).
• If the test lamp lights when one test probe is
placed on the commutator and the other test
probe is placed on the armature core or shaft,
the armature is grounded.
7. Brushes for wear. If the brushes are worn to half
the size of a new brush, replace the brushes. On
the SD-260,'the brushes and brush holders are an
integral part of the frame and field assembly, so the
assembly must be replaced.
F1970
Figure 15— Checking the Field Coils for Opens
8. Brush holders for dirt or damage.
• Make sure that the brushes are not binding in
the holders.
9. Brush springs for distortion or discoloring. If the
springs are weak, bent, or discolored, replace
them. On the SD-260, replace the frame and field
assembly.
10. Field coils.
• Look for burned or damaged insulation, dam­
aged connections or loose poles. If the condi­
tion of the coils is doubtful, replace them. On
the SD-210 and SD-260, replace the field and
frame assembly.
11. Field coils for grounds.
• Connect a self-powered test lamp between the
field frame and the field connector (figure 14).
Make sure the brush ends do not contact the
field frame.
— If the test lam p lights, the fie ld coils are
grounded and must be repaired or replaced.
On the SD-210 and SD-260, the field and
frame assembly must be replaced.
12. Field coils for opens.
• Connect a self-powered test lamp between the
field connector and each of the positive brushes
(figure 15)
— If the test lamp does not light at both
brushes, the field coils are open.
(SD-300)