Richardson's handbook of projection (1930)

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MANAGERS AND PROJECTIONISTS 1357 order to send a comparatively large current through the contacts of the switches, so that any high resistance will be discovered. The voltmeter draws so little current that resistance at the contacts would not show up unless they were so bad that it was nearly an open circuit. Use only \y2 volts to test, or, if using a storage battery, 2 volts. l>e sure that the film disc switch is on disc and that the two keys at the top of the fader are in their proper position. When working on these switches, be very careful not to bend any of the blades, unless it is seen that they do not touch each other properly; if such is the case, proceed very slowly and be sure of what you are doing, for -if you should get two or three of the blades all out of shape you are in for a world of grief. In testing the film attenuator and the circuits associated with it, i.e., all the wiring and apparatus between the output of the film amplifier and the input to the film disc transfer switch, it is very necessary to see that the output of the amplifier is not shorted at the 6-pole switch. The output is marked on the switch. It is connected to the long stationary contacts that are bellied out, and to the corresponding movable blade. Sometimes these two are in contact when the switch is in the off position, and on some switches they are still in contact if the switch is not entirely closed. The methods of testing the circuits betwreen the PEC amplifier and the fader are quite similar to those used when looking for trouble located between the disc pick-up and the fader. Shorts or grounds again kill the signal. One side of this circuit is also grounded in the fader. The point to remember when testing for continuity is that an open circuit in the line going to the attenuator