In case of SPU equipments, if the tubes of the voltage amplifier and the exciter lamps in the projector do not light, the trouble may be due to a discharged storage battery. This can be checked by changing the four-pole double-throw battery switch to the other position. If changing over the battery switch does not cause the tubes to light, the indication is that there is a short-circuit or open circuit in the "A" battery line.

Of course this test cannot be made on the PG-1, PG-2, and PG-13 equipments. In case the voltage amplifier tubes and the exciter lamps fail to light on these equipments, the fuses in the low voltage generator circuit should be checked. If the fuses burn out immediately when replaced, the indication is that there is a shortcircuit in the low voltage generator circuit.

245. Short-circuit on the Voltage Amplifier "A" Battery Line of SPU Equipments. -In case of a shortcircuit on the voltage amplifier "A" battery line, the tubes of the voltage amplifier, the pilot lamps, and the exciter lamps of the projector will not light. If the short-circuit is between the storage battery and the four-pole battery switch, the tubes and lamps will light when the battery switch is changed to the other position. (In no case should the storage battery be left short-circuited. If opening the battery switch does not clear the short-circuit the batteries should be disconnected at the battery terminals.) If the tubes and lamps cannot be lighted check the fuses in the four-pole battery switch box. If changing the position of the four-pole switch does not permit the tubes and lamps to be lighted, check the fuses in the four-pole battery switch box. If they are "blown," test for the location of the short-circuit as follows:Turn the battery switch "off" and disconnect the plugs to the input control panel. Insert new fuses to replace those "blown" and turn the battery switch "on." If the fuses burn out make the same test with the other voltage amplifier in the circuit, and reconnect the plugs on the input control panel, one at a time, and note under what conditions the fuses burn out. The trouble will be found to be in the part of the circuit which "blows" the fuses when connected.

If fuses "blow" when either voltage amplifier is connected in the circuit and the plugs are out of the input control panel, the indication is that the "short" is either in the connection between the four-pole switch and amplifier rack or in the cables connected to a plug of the input control panel. However, it is very improbable that such a short-circuit should occur.

If the fuses "blow" when one of the voltage amplifiers is connected and not when the other voltage amplifier is connected, the short is in the voltage amplifier unit which is connected when the fuses blow.

If the fuses do not "blow" until one of the plugs is reconnected to the input control panel, the indication is that the "short" is between the particular plug which causes the fuses to "blow" when it is reconnected, and the projector, or in the projector itself. The most probable location of such a "short" is in the projector itself. If the fuses "blow" when one of the plugs is reconnected to the input control panel, leave the plug in and turn the exciter lamp-rheostat associated with it to its "Off" position and make the same test again. If the fuses do not "blow" under this condition, the equipment can be operated from "disc" but not from "film," except that it can be operated from "film" using the other projector only.

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