Replacement of Power Modules and Output Diodes
Input rectifier, D13, is a power module. When mount- ing power modules, the heat sink and module mount- ing surface should be clean and free of burrs and for- eign material. Apply heatsink compound (Dow 340) as a uniform layer ideally .010” thick, to eliminate all air pockets. This may be verified by mounting and then removing the module. When removed, the compound on both surfaces will appear textured as if a vacuum had created veinlike ridges when the parts were sepa- rated. If the compound does not have this appear- ance, apply more heatsink compound and recheck.
Replacement of output diodes D1 thru D12 is similar. Clean and brighten mounting surface with fine steel wool. Compound should be used on surface between diode and heat sink when mounting individual diodes.
The compound should be applied to the heat sink in a very thin layer, less than 0.001 in. DO NOT apply on diode stud and mounting nut threads.
Components must have proper torque applied to mounting screws and to electrical terminals. Torque the modules according to the following:
| Component to Heat Sink | Terminal |
Component | Torque ±10% | Torque ±10% |
Switch Board |
|
|
Module | 44 Inch - Lbs.(1) | N.A. |
| (5N - m) |
|
Capacitor | N.A. | 55 Inch - Lbs. |
|
| (6.3 N - m) |
Input Rectifier | 6 Inch - Lbs.(2) | 26 Inch - Lbs. |
(0.7 N - m) | 3 (N - m) | |
Output Diode | 25 Inch - Lbs. | N.A. |
(3 N - m) |
|
(1)Retorque after 3 hours to allow for spread of compound.
(2)Tighten in staggered fashion one quarter turn at a time.
Environment Protection
High voltage connections are covered with an RTV sealant to prevent malfunction in severe environ- ments. Sealant must be applied to connections which have been opened or otherwise lost their protection. A noncorrosive electronic grade sealant such as Dow Corning 3140, 3145, 738, Columbus Adhesives 0172 or GE
High voltage areas which require sealant are as listed: - Input rectifier D13, all 5 terminals.
Printed Circuit Board Replacement
1.Handle PC Boards by edges only.
2.Store PC Boards only in the bags that disperse static charges.
3.Inspect PC Board for burned conductors or com- ponents. If damage is visible, inspect the machine wiring for grounds or shorts to avoid damaging a new PC Board.
4.If there is no visible damage to the PC Board, install a new PC Board and see if the problem is fixed. If the problem is fixed by the new board, reinstall the old board and see if the problem reoc- curs. If the problem does not reoccur, check the wiring harness and plugs for loose connections.
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