Points to Look For

(1) First of all, find out what type of power supply your set has. The power

supply you'll use may be any of the following: Rectifier type, battery,

dynamotor, or vibrator.

(2) These are a few checks that you can make, regardless of the type of set

you're working on.

Check the power supply input circuit.

Make a

continuity check for open or shorts in the input cables, ac line cords, or

on-off switches.

Don't overlook fuses, as a burned-out fuse may be the

only trouble.

A continuity check should also be made of the output

circuit of your power supply. Remember, a continuity check is always made

with the power off.

(3) Then turn on your set and see if the B plus voltage is normal.

Use your

voltmeter to make this check.

e. Points to Look For.

Here are a few specific points to look for in the

various types of power supplies:

(1) Rectifier type.

Check all cables leading to or from the power supply.

Then check for the following:

(a) Bad rectifier tube.

(b) Open filter choke in the power supply.

(c) Filter choke shorted or choke leads shorting to chassis.

(d) Open or shorted power transformer windings.

If shorted, there is a

good possibility the fuse will blow.

(e) Shorted filter capacitor.

If this is the trouble, the rectifier tube

will glow with a bright red color and probably burn out.

(f) A short or open in the B plus line leading to any stage using power

from the power supply.

If shorted, there is a good possibility the

fuse will blow. If open, the voltage will be removed from the stage.

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

(2) Battery type.

If your set is battery-operated, then noisy, weak, or

unstable operation is usually caused by weak batteries. Be on guard for

signs of corrosion around battery terminals. If the supply voltage is not

normal, replace the batteries without checking further.

If your set is

not going to be used for a long period of time, remove the batteries.

(3) Vibrator type.

The function of a vibrator is to change a steady dc

voltage to a pulsating dc voltage.

This pulsating dc voltage is then

converted to a higher ac voltage by a step-up transformer. Most vibrator

supplies contain a vibrator, a power transformer, a rectifier, and a

filter.

Complete inoperation is usually caused by a defective vibrator.

If the vibrator is operating normally,

322 L5

38