a. Repair of Pressure Plate. Replace if damaged.

NOTE: To remove the pressure plate, slide it lengthwise as indicated by the arrows in

fig. 4-29 A . Lift up the end (fig. 4-29 B ) until the spring is free. To install the pressure plate, hook one end in the spring, and lift the free ends of the spring with tweezers. Engage the other end of the pressure plate.

b. Checking Pressure Plate. Depress the pressure plate with the fingers, and check for adequate and even pressure.

4-16. Baseplate Assembly

(Fig. 22)

a. Film Positioning Disc. Replace if damaged.

b. Loch Assembly. Replace damaged parts.

c. Tripod Bushing. Replace baseplate.

d. Baseplate. Replace baseplate if it is badly dented, or bent out of shape.

Section II. EXPOSURE METER

4-17. General

In so far as possible, determine the repairs to be made before disassembling the exposure meter. Reference to chapter 2, section 2 (troubleshooting) will assist in isolating the component requiring repair or adjustment. Disassembly beyond that necessary should be avoided. In most instances, sub-assemblies become accessible by removing the housing (par. 3-10). Worn or damaged parts should be replaced before reassembling the exposure meter. Parts to be cleaned, lubricated or adjusted must be removed. Before testing the meter, set the indicator needle to mechanical zero, as described in TM 11-6720-244-12, paragraph 4-5c(5).

4-18. Battery Test Circuit

(Fig. 40)

Test the battery as described in TM 11-6720-244-12, paragraph 4-5c and figure 3-6. If the indicator needle does not rest on, or slightly beyond, the battery-test index, proceed as follows:

a. Replace the battery.

NOTE: Select a replacement battery that measures 1.35 volts.

b. If the indicator does not reach the index (with fresh battery installed) replace resistor (Rl). (Value of the resistor should be 2,000-ohms).

c. If the indicator rests much beyond the index, replace resistor (R2). (Value of the resistor should be 100-ohms).

4-19. Coil assembly

(Fig. 40)

If the exposure meter readings are erratic, or if there is no indication, proceed as follows:

a. Desolder red lead from the coil assembly.

b. Check coil resistance and continuity with a multi-meter. Coil resistance should be approximately 1,500-ohms.

NOTE: Place the multi-meter probes on the coil assembly frame and coil point from which the lead was desoldered.

If the coil indicates an open circuit, or ground, replace the entire meter circuit insert (13).

c. Resolder red lead after checking coil. 4-20. Switches and Battery Contact

(Fig. 41)

If the coil assembly is not defective, proceed as follows:

a. Clean and adjust contact points of switch (1).

b. Clean and adjust contact points of switch arm (6).

c. Adjust battery housing spring tension.

4-21. Photo-Resistor (CdS cell)

Check the cell as follows:

a. Place a fresh battery, or one known to be of full voltage, in the exposure meter.

b. Completely cover the meter cell window with the finger, or other opaque material.

c. Actuate the exposure meter release button and note the deflection of the indicator needle. It should not move into the first black sector of the light-intensity scale.

NOTE: The meter indicator needle should be set to mechanical zero before making the test.

d. If the indicator needle deflects into, or past, the first black sector replace the entire meter circuit insert.

4-22. Checking and Calibration

CAUTION: The test instrument (42-655.01-Z1W7), calibration test instrument (42-655.01-Z1W22) and voltage regulator (KH10) should be turned on and twenty minutes allowed for stabilization.

a. Place the 1.33-volt battery substitute (part of calibration test instrument 42-655.01-Z1W22) in the meter battery housing.

b. Place the meter cell window tightly against the illuminating window of test instrument 42-655.01-Z1W7.

NOTE: All extraneous light should be excluded from the test instrument illuminating window and the meter cell window.

c. Set the meters film speed index to ASA 25, the sensitivity switch to the black index, and the shutter speed scale to 1/8-second.

d. Set the left button of test instrument 42-655.01-Z1W7 to its low-light position. Depress button number 8.

e. Actuate the exposure meter release button. The indicator needle should align with f/5.6 on the black aperture scale. If it does not, proceed as follows:

(1) Remove housing (par. 3-10).

(2) Adjust potentiometer (P1), fig. 40.

(3) Replace housing, but do not secure. Note that indicator needle aligns with f/5.6 on the black aperture scale. If it does not, readjust potentiometer until it does.

f. Set the meters film speed index to ASA 25, the sensitivity switch to the red index, and the shutter speed to 1/8-second.

g. Set test instrument 42-655.01-Z1W7 as described in paragraph d above, and position meter as described in b above.

h. Actuate the exposure meter release button. The indicator needle should align with f/5.6 on the red aperture scale. If it does not, adjust potentiometer (P2), fig. 40.

i. Repeat the test-adjusting procedures for low and high sensitivity meter settings until the readings are correct. If correct readings cannot be obtained by adjusting the potentiometers, replace the entire meter circuit insert (13), figure 40.

j. Check the exposure meter indicator needle readings through the entire range as follows:

(1) Place the meter cell window tightly against the illuminating window of test instrument 42-655.01-Z1W7 and actuate the exposure meter release button.

(2) Set the test instrument light level, and depress the numbered button as indicated in the table below. Set the exposure meter film speed index to ASA 25; set the meter sensitivity index, and shutter speed scale index to correspond with the test instrument settings indicated in the table. The meter indicator needle should point to f/5.6. A tolerance of l/2-f/8top is permissible.