![]() ![]() I'm not sure I got those settings exactly right (with the meter off the camera), but you should be able to see the ends of the potentiometer element easily, and check for maximum and minimum resistance at the crossover. 370K (maximum), and at around f/16, 1/1000 sec, ASA 40 it is approx. At somewhere around f/2, 1 sec, ASA 100 it is approx. ![]() The aperture lever, which moves the wiper, and the shutter speed & ASA setting, which turns the potentiometer resistive element, operate the main potentiometer. The meter is centered when there is a voltage of. In meter mode, with the pushbutton up, the switch yellow, red, and white leads connected, the voltage divider is the two CdS photocells (60% center and 40% full frame) and the fixed 41 ohm resistor, against the main potentiometer and the meter (with trimpot) in parallel. If the meter is open, full battery voltage will be imposed on the meter with no meter movement. The best way to check the meter for continuity is to check voltage from the meter lead to ground with the battery installed and the meter switch in the battery test position. All potentiometers and the resistor can safely be checked with an ohmmeter if you test with the battery removed and the switch off, and read directly across a single potentiometer. Be careful not to put an ohmmeter across the meter even indirectly. 025 volts at 16 micro-amps is much less than what an ohmmeter will put out. This means the meter movement is about 1560 ohms (.025/.000016), and that the voltage at the switch is about. With a 2.7 volt battery this results in a current of about 16 micro-amps ((2.7. When the test button is pressed, current flows from battery negative, through test adjust trimpot, through the switch (green to white, pushbutton down), through the meter adjust trimpot, and then through the meter to case ground to battery positive. The meter movement is centered when it has 0.025 volts across it. In both test and meter modes, the circuit is a voltage divider. ![]() ![]() How the Nikon FTn lightmeter works: Refer to the schematic below. It was prepared without any information from Nikon, Inc., and is provided without any guarantee as to completeness or accuracy. Nikon FTn meter adjustment and cleaning procedure About this document: This document was prepared by a camera repair hobbyist as an aid to other camera repair hobbyists. ![]()
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