Adjustment Procedures

Figure 5-5. Power Supply PP-3940/G, rear view.

(4) Set controls R23, R24, and R44 to

5-3. Adjustment Procedures

their midrange position (fig. 5-3).

Note: Perform the procedures given in paragraph

c. Procedure.

5-1 before peforming these instructions. These pro-

(1) Connect the dc voltmeter test leads

cedures should be performed whenever it is necessary

to replace faulty (fig. 5-1 and 5-2) transistors.

between the right side of resistor

a. Initial Requirements.

R45 on the outer component board

(1) Be sure that a coating of heat-trans-

and to the left (negative) terminal

of dc voltmeter M2 (fig. 5-3).

ferring silicon grease is used between

the power transistor insulators and

(2) Connect the ac voltmeter test leads

their heat sink (applicable to tran-

to the terminals indicated in (1)

sistors Q7, Q10, and Q16 and pass-

above.

ing stages).

(3) Set the ac voltmeter dc range switch

(2) Check all terminals of transistor Q7,

to 50-volt range. (Set up the meter

for normal vacuum-tube voltmeter

Q10, or Q16 for continuity to the

best sink before connecting any wires

(vtvm) operation as described in TM

to the transistor collector, emitter,

11-6625-438-10.)

and base terminals. All elements of

(4) Set the ac voltmeter range switch to

the lowest ac volt range (0.001 volt).

these transistors should be electrical-

ly insulated from the heat sink as-

(5) Turn the power supply POWER

sembly.

switch S1 to ON.

(3) In replacing the passing stage power

(6) Adjust resistor R44 for a dc reading

of 6.0 to 6.1 volts on the dc voltme-

transistors, observe the same precau-

ter. The meter reading should be not

tions as described above. (All tran-

higher than 50 microvolt root mean

sistors must float above chassis

square (rms).

ground.)

(7) Connect the power supply power line

b. Initial Control Settings.

(1) Turn the COARSE ADJ. control fully

cord to the output of the variac. Use

Multimeter TS-352/U across the var-

counterclockwise (fig. 2-1).

iac secondary to monitor the ac volt-

(2) Loosen the shaft coupling setscrews

age.

between variac T1 and variable re-

(8) Connect the variac to a power source

sistor 30 (fig. 5-1).

and turn on the power supply POW-

(3) Set the FINE ADJ. control fully coun-

ER switch.

terclockwise (fig. 2-1).

5-7