TM 9-6115-658-13&P 4-8 Figure 4-3.  Unit PMCS Routing Diagram. Table 4-1.  Unit Preventive Maintenance Checks and Services ITEM NO. INTERVAL ITEM TO BE CHECKED OR SERVICED PROCEDURE NOT FULLY MISSION CAPABLE IF: Before performing any maintenance that requires climbing on   or under trailer, make sure that trailer handbrakes are set,   trailer front landing leg/support leg is lowered, and leveling- support jack is lowered.  Injury to personnel could result from   trailer suddenly rolling or tipping. 1 Semi- Annually POWER CABLES   Inspect power cables for worn, frayed,   or cracked insulation, loose terminal lugs, and loose connections.  Tighten as needed. Power cable is unserviceable. 2 Semi- Annually SWITCH BOX ASSEMBLY   Inspect switch box assembly (refer to paragraph 4-13). 3 Semi- Annually MOUNTING RAILS Inspect for cracks and deformation. Mounting rail is cracked or deformed. 4 Semi- Annually FIRE EXTINGUISHER a. Inspect for broken seal and damage to handle. b.  Weigh to determine whether charge is sufficient.  Weight is 13 pounds when fully charged.  If weight is 12.5 pounds or less, send to specialized activity for recharging. Fire extinguisher not charged. WARNING