Dynamotor type

you'll hear a slight buzz.

If you touch a properly operating vibrator,

you'll also feel a slight vibration. One word of caution: if you replace

a vibrator, always put in a new buffer capacitor.

Other troubles are

similar to those for any conventional ac operated power supply. They are:

(a) Bad rectifier tube.

(b) Open or shorted power transformer windings.

(c) Open filter choke.

(d) Shorted or leaky filter capacitor.

(e) A short in the B plus line leading to any stage using power from the

power supply.

(f) Open bleeder resistor (if used as voltage divider also).

(4) Dynamotor type.

You'll find that dynamotor-type supplies are used in

practically all Army aircraft, and in many vehicular installations.

Except for the values of the component parts, filter circuits used in

dynamotor power supplies are similar to those in rectifier units. Always

disconnect the dynamotor at the output terminals before you make any

resistance measurements in the filter circuit. Then you will be able to

make an accurate resistance check of the filter circuit components. Some

trouble points to check when examining a dynamotor power supply follow:

(a) Low battery voltage source.

(b) Loose power cable connection, or wrong cable connections.

(c) Worn dynamotor brushes.

Replace those that are less than 1/4 inch

long, measuring from the commutator to the brush pressure spring.

Watch the polarity mark when replacing worn brushes and watch for

broken or loose brush pigtails.

(d) Dirty or worn commutator.

If the dynamotor commutator is accessible,

hold a piece of fine sandpaper against the commutator while the

dynamotor is operating.

WARNING:

Don't use this method if the dynamotor puts out a high

voltage like the 1,000-volt dc output in Radio Set AN/GRC-19.

(e) Open or shorted armature windings.

f. Operational Check. Now that you've made a good visual inspection and checked

the key circuits for shorts, you're ready to make the operational check.

This

check will help you sectionalize trouble in your receiver or receiver-transmitter.

All this test consists of is operating the equipment

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