Of course, the above tests can not be made as outlined if no plugs are used in the input control panels, but a similar test can be made by turning the exciter lamp rheostats to their "Off" positions instead of disconnecting the plugs. Under this condition the procedure is the same except that the rheostats are turned "on", one at a time, instead of reconnecting the plugs.

246. Short-circuit on the "A" Supply Line of a PG-1 Equipment. -In case of a short-circuit on the "A" supply line of a PG-1 equipment the fuse in the 15-volt generator circuit will blow, and the filaments of the voltage amplifier tubes, the power amplifier tubes and the exciter lamps will not light. Since the PG-1 has a complete duplicate amplifier and power supply equipment, it will be necessary to isolate the defect immediately unless the short-circuit is in the exciter lamp circuit of one of the projectors.

In case the fuses blow in the low voltage generator circuit of one of the motorgenerator sets, change over to the other amplifier rack. Leave the input switches on the input panel in their "open" positions until the input switches of the rack being shut down have been "opened." Then, as the last operation of putting the rack to be used into operation, "close" its input switches one at a time. If the short-circuit is in the exciter lamp circuit of the projector, the fuses of the 15-volt generator circuit will "blow" when one of the lever switches is closed. The defective projector is indicated by the input switch which causes the fuse to "blow." In case of a short-circuit in the exciter lamp circuit of one projector, the equipment can still be operated for sound-on-film from one projector only and for sound-on-disc. To do this, turn the exciter lamp rheostat of the defective projector to its "Off" position and operate the remainder of the equipment in the usual way.

247. Short-circuit on the "A" Supply Line of a PG-2 Equipment. -In case of a short-circuit on the "A" supply line of a PG-2 equipment the fuses in the 15-volt generator circuit will "blow." To isolate the defective part of the equipment turn the exciter lamp switches to the "Off" positions, open the lever switches on the power amplifier panels and replace the "blown" fuse. If the fuse blows again before any of the amplifier rack switches are closed, the indication is that the short-circuit is either in the voltage amplifier or in the storage battery circuit. The storage battery circuit can be opened by removing the upper of the two 50 ampere fuses in the low voltage generator circuit. See Figure 118. If necessary, the equipment can be operated with the battery disconnected, but an appreciable hum may be heard from the loud speaker. If the fuse does not blow when replaced, close the lever switches of the power amplifier panels one at a time. If the fuse "blows" when one of these switches is closed, the indication is that the short-circuit is in the power amplifier unit with which the switch is used. In this case leave the lever switch of defective power amplifier open and operate using one power amplifier.

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