Troubleshooting guide

A. Visual Analysis For Defective BR/BBR Components.

1. Remove top and left side panels of Power Source. Inspect the 500 A BR fuse links (F3 and F4) mounted in

the Main Transformer secondary bus bars to see if they have blown. If not blown, check the 30 A BBR

cartridge fuses (F1 and F2) with an ohmmeter to determine if they are open.

2. If either or both of the fuses protecting its respective bridge assembly are open, it's a sign that one or more

of the diodes or SCRs in that particular bridge may be shorted.

3. Refer to figure 3-1 for the makeup of a fuse and information to prevent hardware from loosening due to thermal

cycling.

NOTE

Figure 3-1 depicts one end of one fuse. The other end is the same.

MAINTENANCESECTION 3

BUS BAR

NOTE 3

NOTE 4

FUSE

NOTES 1 & 2

FUSE SUPPORT

4. Check for cracked or broken ceramic around each diode pigtail of SCR body. If cracked, it's a sign of a shorted

diode or SCR. When the larger diodes or SCRs fail, they most commonly fail shorted.

B. Testing Main Bridge Rectifier (MBR) Assembly.

The Main Bridge essentially contains three groups of components to be tested: Power Diodes D4, D5, and D6;

Freewheeling Diode D7; and SCRs 4, 5, and 6. The group testing sequence does not require electrical isolation;

however, to determine the specific faulty component in a group, some form of isolation may be required as follows:

1. Checking Power Diode Group D4, D5 and D6.

(a) If fuse links F3 and F4 are not blown, use an ohmmeter set at its lowest resistance scale and check

the diode group as described in step 1.(c). Checking any one diode within the group will determine

if the group is good or if a shorted condition exists. If there is a short, you must electrically isolate to

Figure 3-1. Fuse Assembly

NOTES:

1. Fuse link must be in direct contact with copper bus bar (no hardware in between).

Apply electrical joint compound between fuse link and bus bar.

2. Wire brush bus bar and fuse link at mating point prior to installing to prevent

overheating and to ensure good electrical contact.

3. Any 1/4-inch bolt or screw is usable if threaded completely to head or within 1/4 inch

of head. A 1/4-inch threaded rod may be substituted for bolt or screw.

4. It is critical that a space (one full turn) remain between nuts.