Isolation Diode Test

TM 5-4110-217-14

(4)

Connectohmmeter to bracket and

NOTE

grounded brush. Resistance reading should be zero

A shorted stator coil (20) to core would appear as a

Repeat same test on brush lead wire as described In

shorted negative rectifier diode assembly (14)

paragraph (3) above

c Isolation Diode Test (fig. 5-9). If a commercial

(2) To check the positive diode assembly (15),

diode tester is used, follow tester manufacturer's testing

connect test probes to regulator (auxiliary) terminal and

Instructions. If a commercial tester is not available, use

the first diode left of brush cover. Then reverse test

a 12 volt DC test lamp. Connect the test lamp to output

probes. The same procedure and results apply as in

terminal and auxiliary terminal of isolation diode (1) Then

paragraph (1) above

reverse test probes The test lamp should light in one

NOTE

direction but should not light in the other direction. If the

If the above procedures do not find the

test lamp lights in both directions, the isolation diode is

difficulties In the alternator, replace with a new

shorted. If the test lamp does not light in either direction,

alternator

isolation diode is open. Repeat test after Isolation diode

has been removed to ascertain findings d.

In-Circuit

f. Installation. Refer to paragraph 3-46h and install

Rectifier Diode Test (fig. 5-9). Any commercial in-circuit

alternator

diode tester will suffice to make the check Follow tester

5-5 Carburetor.

manufacturer's recommended testing procedure If the In-

a. Remove the carburetor (fig. 5-10) as instructed

circuit tester indicates that the diodes (14) and (15) are

in paragraph 3-26.

faulty, recheck diodes individually after diode assemblies

b. Disassemble the carburetor as illustrated on

have been disconnected from stator assembly (20).

figure 5-10.

Shorted stator coil (20) or shorted insulation washers

c. Clean all carburetor parts with an approved

(18) or sleeves (16) on positive diode assembly (15)

solvent. Pay particular attention to all air and fuel

would make diodes appear to be shorted.

passages. Dry all parts with compressed air

(1) To check negative diode assembly (14),

d. Inspect all carburetor parts for damage or

connect tester to ground terminal and first diode to right

deterioration.

Replace all defective parts during

of brush cover. Then successively check between

reassembly.

ground terminal and second diode to right of brush cover

NOTE

and ground terminal and third diode to right of brush

Check the carburetor float level in the following

cover.

manner.

With the carburetor top casting

(2) To check the positive diode assembly (15),

inverted, gasket, float and needle valve

connect tester to regulator (auxiliary) terminal and first

installed, measure distance between gasket

diode to the left of brush cover. Then successively

and top edge of float (bottom edge when

check between regulator terminal and second diode to

inverted. With float resting lightly against the

left of brush cover and regulator terminal and third diode

needle in its seat measurement, there should

to left of brush cover

be 5/16" between the float and gasket on the

e. Rectifier Diode Test Using a Test Lamp (fig.5-9).

free end (opposite end from needle valve) of

A test lamp will not indicate an open condition unless all

the float. If adjustment is necessary, the lip

three diodes of either assembly are open However, a

(next to needle) should be bent very carefully.

shorted diode can be detected. This test is not 100

e Using the carburetor repair kit, reassemble the

percent effective but can be used if so desired when an

carburetor

in-circuit diode tester is not available. Use a 12 volt DC

f. Install the carburetor and adjust the idle and high

test lamp only, otherwise diodes will be damaged.

speed needles as described in paragraph 3-26.

(1) Connect test lamp probes to ground

5-6. Gasoline Tank.

terminal and first diode to right of brush cover, then

a. Draining Gasoline Tank (fig. 3-23). Place a

reverse test probes. The test lamp should light In one

clean empty container under fuel tank plug (16).

direction but not in the other direction If the lamp lights in

Remove plug (16) and drain tank (12). Replace

both directions, one or more of the rectifier diodes of the

plug after draining.

assembly being tested are shorted. If the lamp does not

b. Removal. Disconnect fuel lines from gasoline

light in either direction, all three diodes in the assembly

tank Loosen two straps (13) holding tank to refrigeration

are open Recheck diodes individually after disassembly

unit. Lift out tank.

to ascertain findings.

c. Cleaning and Inspection.

(1) Flush gasoline tank with approved cleaning

solvent.

Clean exterior of gasoline tank with an

approved cleaning solvent. Dry exterior thoroughly.

Change 3 5-5