Nikon DP-1 adjustment and cleaning procedure

Nikon DP-1 meter adjustment and cleaning procedure

By Glen Walpert, May 1999

About this document:

This document was written by a camera repair hobbyist as a random act of senseless kindness. It
was prepared without any information from Nikon, Inc., and is provided without any guarantee
as to completeness or accuracy.

How the Nikon DP-1 lightmeter works:

Refer to the schematic below. In both test and meter modes, the circuit is a voltage divider. The
meter movement is centered when it has about 0.025 volts across it, at about 16 micro-amps.

When the test button is pressed, current flows from battery negative, through test adjust trimpot,
through the switch and then through the meter to case ground (battery positive.

CAUTION: Note that .025 volts at 16 micro-amps is much less than what most ohmmeters will
put out. Be careful not to put an ohmmeter across the meter even indirectly. Checking the ring
resistor or meter adjust resistor with an ohmmeter can destroy the meter movement, if the battery
test button is not pressed to disconnect the meter from those resistors during resistance checks.
Checking the meter directly with an ohmmeter is very likely to destroy it. It is best to perform
resistance of the ring resistor or meter adjust resistor with a small plastic or paper strip holding
the test switch in the middle position, connected to neither the normal or test contacts.

The best way to check the meter for continuity is to check voltage across the meter with a 3 volt
or less battery temporarily clipped with - to the meter top half test contact and + to the ground
contact (the ones that connect to the meter bottom half). Press the test switch to complete the
normal test circuit. If the meter is open, full battery voltage will be imposed on the meter with no
meter movement.

In meter mode, with the test button not pressed and the camera power switch on, the voltage
divider is the two CdS photocells (60% center and 40% full frame) and the CdS trim resistors,
against the main potentiometer and the meter adjust trimpot.

The aperture lever, which moves the wiper, and the shutter speed & ASA setting, which turns the
potentiometer resistive element, operate the ring resistor. At somewhere around f/1.2, 2 sec, ASA
400 it is approx. 495K (maximum), and at around f/32, 1/2000 sec, ASA 400 it is approx. 0.6
ohms (minimum). 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.

There are no stops, the potentiometer will wrap around from maximum to minimum at long
exposures and wide apertures, causing the meter to stop functioning (needle will drop to off

position).
The photocell resistance (both cells) varies from over 4 million ohms in a fairly dark room to less

than 200 ohms when the meter is held about 6 inches from a 60-watt bulb.
The above measurements are from a single working meter. Small variance can be expected from

meter to meter.

Nikon DP-1 Meter Schematic

Troubleshooting:

Check your batteries, they should be about 1.5 volts each, and you should have -3 volts on the
meter power contacts at the top of the camera body when the film advance lever is pulled out to
the on position.

Meter completely dead - this could be an open circuit anywhere, including the meter movement.
Check the entire circuit.

Test function works but meter reads erratically or not at all - bad contact on main potentiometer
or poor connection; disassemble, inspect and clean.

Adjustment (meter on camera):

Peel off the leather meter cover and remove the small oval metal plate covering the adjustments.
Two trim potentiometers will be accessible, the left trim is for meter test and the right trim is for
meter sensitivity. The adjustments are independent and can be done in any order.

(Note: It is not necessary to remove the leather cover to disassemble and clean the DP-1.)

Fig. 1 - DP-1 adjustment locations

Adjustment should be done with fresh batteries.
Set the meter test trim so that the needle is centered when the test button is pressed.
Focus the camera (full frame) on an evenly illuminated 18% gray card, and adjust the sensitivity

to agree with a known accurate meter. If you don't have a known accurate meter, you can make
an approximate setting by using film manufacturers recommended setting for direct sunlight. For
example, set the camera to ASA 100, 1/125 sec, f/16, and adjust the meter to center the needle
when aimed at a gray card in direct sunlight. You could then make fine adjustments based on test
shots, for example, if tests indicate you need 1/2 stop more exposure, set up with the gray card,
center the needle, open up 1/2 stop, and re-center the meter using the sensitivity trim adjustment.

The two CdS trimpots are only accessible with the meter disassembled. These trimpots should
only need adjustment if the CdS cells are replaced, and the adjustment would normally be done
with a calibrated light box. If you check the meter sensitivity over it's full range, and find that the
meter is off at the ends after adjusting the main sensitivity adjustment to be correct in the middle,
it should be possible to trim the dark or bright sensitivity with a trial-and-error procedure.
Decreasing the resistance of either trim will increase the meter sensitivity at that end.

If meter cannot be adjusted, disassemble, clean and inspect.