Operating instructions

6.1.7 Brakes

Braking is accomplished primarily through the servo control of the reel

motors. As a safety backup in case of power failure, mechanical brakes have

been provided. A padded felt band is spring loaded against a brake drum

attached to the reel motor shaft. The felt band is held away from the brake

drum during Play, Record, Fast Forward, and Rewind modes. Only during

Unload mode and when the power is off, do the brakes engage. The

mechanism is designed so the holdback tension is greater than the feed

tension (i.e., for the Supply reel motor, the counterclockwise tension is

greater than the clockwise tension, and vice-versa for the Take-up reel

motor). Repeat the following procedure for both the Supply and Take-up reel

brakes. Refer to Figure 6-6 and Figure 6-7.

1. Turn off the power to the machine.

2. Mount an empty 10" reel on the reel table.

3. Attach about 70 cm (2 feet) of string to a spring scale (spring gauge).

4. Check the holdback tension by winding the free end of the string around

the reel hub (clockwise for Supply reel, counterclockwise for Take-up

reel) and pulling on the spring scale to unwind the string. Read the

tension while steadily pulling the spring scale to unwind the string.

Since the reading on the spring scale is dependent upon the speed at

which the string is pulled, two or three measurements should be taken

and averaged. The tension should be 600 to 1000 grams (Figure 6-6).

SUPPLY REEL

SPRING GAUGE

STRING

TAKE-UP REEL

A: FEED TENSION

B: HOLDBACK TENSION

Figure 6-6

Measuring Brake Tension

BRAKE BAND

BRAKE DRUM

BRAKE

SOLENOID

Figure 6-7

Brake Tension Adjustment Nut

Section 6 Alignment

6 - 10

October 1990

MTR-90III Operation and Maintenance Manual