Distortion Measurement Check

TB 11-6626-620-35-2

(19) Depress Test Instrument RESET switch.

4-1. Distortion Measurement Check. a. Per-

(20) PERCENT DISTORTION meter shall in-

formance Check.

dicate 0.

(1) Slowly adjust the pattern generator %

(21) Set Test Instrument POLARITY switch to -.

DISTORT control from O to 50.

(22) PERCENT DISTORTION meter will in-

NOTE

dicate beyond 25%.

The % DISTORT control must be moved

(23) Depress Test Instrument RESET switch.

slowly so that the meter pointer will not

(24) PERCENT DISTORTION meter will in-

jump to off scale. If the meter pointer

dicate 25%.

jumps to off scale, press the RESET button

(25) Make the Test Instrument and pattern

and repeat the % DISTORT control ad-

generator switch settings shown in table 4-1, and in-

justment.

dications shall be as indicated therein.

(2) The Test Instrument SIGNAL lamp shall

Table

4-1.

Distortion

Measurements

flicker, LATE lamp will light and PERCENT

Test Instrument

DISTORTION meter indicator shall follow control O

Pattern generator

Indication

to 50.

RATE switch

PERCENT DISTORTION

RATE switch

(3) The indication on the PERCENT DISTOR-

(bauds)

meter (%)

TION meter shall move from 0 to 49.2% distortion in

63 increments (this is derived from a binary count cir-

7.5/45.5 . . . . .

*24 t0 26

45.5 . . . . . .

7.5/50 . . . . . . .

24 to %

50 . . . . . . . .

cuit).

7.5/74.2 . . . . .

74.2 . . . . . .

24 to 26

(4) Set the Test Instrument DISTORTION

7.0/150 . . . . . .

150 . . . . . . .

20 to 25

SELECT switch to MARK/SPACE.

(5) Depress Test Instrument RESET switch.

* Depress Test Instrument RESET switch to obtain each

(6) PERCENT DISTORTION meter indicator

shall drop to 0.

indication.

(7) Set the pattern generator DISTORT SELECT

b. Adjustments.

switch to BIAS MARK and % DISTORT control to O.

(1) With power cord disconnected, remove Test

(8) Set the Test Instrument DISTORTION

Instrument from case.

SELECT switch to SPACE/MARK.

(2) Remove (12) screws from top panel of the Test

(9) Slowly adjust the pattern generator %

Instrument.

DISTORT control from 0 to 50.

(3) Remove card 1A2A15 from the Test In-

(10) Test Instrument EARLY lamp light and

strument. Remove extender card 1A2A7 from dummy

PERCENT DISTORTION meter indicator shall

socket and insert into 1A2A15 socket.

follow control 0 to 50.

(4) Insert card 1A2A15 into the extender card

(11) Depress Test Instrument RESET switch.

1A2A7.

(12) PERCENT DISTORTION meter indicator

(5) Set RATE switch to 75.

shall drop to 0.

(6) Set CURRENT SELECT switch to 20).

(13) Return the pattern generator to the same

(7) Set FILTER to OUT.

positions as indicated in paragraph 3-3 above.

(8) Set DISTORTION SELECT switch to PEAK

(14) Set the Test Instrument DISTORTION

TOTAL.

SELECT switch to PEAK TOTAL.

(9) Connect the Test Instrument to an AC power

(15) Slowly increase the pattern generator %

source.

DISTORT control from 0 to 40% and then return to

(10) Do not apply an input signal.

20% .

(11) Turn POWER switch to ON.

(16) The Test Instrument PERCENT DISTOR-

(12) Depress the Test Instrument RESET switch.

TION meter indicator shall follow control to 40% and

(13) Connect a lead momentarily between the

remain there until the Test Instrument RESET

chassis and base (2 contact printed circuit board con-

switch is depressed.

nectors) of transistor Q6 on card 1A2A15.

(17) Set the pattern generator % DISTORT con-

(14) Adjust R15 of card 1A2A15 for a 25 percent

trol to 25%.

indication on the PERCENT DISTORTION meter

(18) Set the Test Instrument POLARITY switch

(fig. 4-l). (R)

to +.