Otari MX-5050 Mini Pro

MX-5050B Maintenance Manual — Digital Edition · Part 3 · scan pages 23-30

Tape Transport Maintenance

Tape transport maintenance includes procedures for adjusting the supply and take-up reel brakes, the capstan pinch roller pressure and the capstan speed adjustment.

3-1 TRANSPORT ACCESS↑ TOP

To gain access to the recorder transport, proceed as follows:

  1. Remove the power cable and place the recorder in an upright position.
  2. Remove the rear cover by removing the six cross-recessed screws on the panel (two screws are with studs.)
  3. Open the control printed circuit board by removing six cross-recessed screws marked "OPEN".
  4. Remove the two side panels by removing the four hex-socket screws on each panel. Fig. 3-1 Tape Transport Access: an exploded view of the cabinet: perforated top and bottom panels and two side panels drawn away from the chassis, each with its mounting screws⤢ zoomFig. 3-1 Tape Transport Access: an exploded view of the cabinet: perforated top and bottom panels and two side panels drawn away from the chassis, each with its mounting screws

BRAKE ADJUSTMENT

The brake system on each reel, stops reel rotation when the stop mode is entered into or when power is removed. The brakes are checked and adjusted with the power removed. Since the brake force is different for each direction of rotation (brake differential), and there is but a single adjustment, the force is checked and adjusted for the best compromise force in each direction.

In the following steps, an empty 10 1/2 inch diameter NAB reel (4 1/2 inch diameter hub) is used and a length of cord or twine is wrapped on the reel. A spring scale is attached to a small loop formed in the free end of the cord or twine.

If 10 1/2 inch diameter NAB reel (4 1/2 inch diameter hub) is not available, a 7 inch diameter reel (2 1/4 inch diameter hub) may be used but all readings must be multiplied by a factor of 2. Proceed as follows:

Refer to table 3-1 for the braking force specifications.

  1. Place an empty 10 1/2 inch diameter NAB reel on the supply reel turntable. Secure with a holddown knob.
  2. Wind a length of cord or twine a few turns counterclockwise on the hub. Tie a loop in the free end of the cord or twine.
  3. Insert the hook of a 0-16 ounce or 0-32 ounce spring scale through the loop and hold the spring scale upright as shown in Fig. 3-2.
  4. Pull on the scale slowly to make the reel rotate counterclockwise (direction "B" in Fig. 3-2). While being sure the cord does not rub against either flange, note the scale reading. The reading should be 7.9 to 9.7 ounces (225 to 275 grams).
  5. Wind the cord or twine in a clockwise direction on the supply reel.
  6. Repeat steps 3 and 4 to make the reel rotate clockwise (direction "A" in Fig. 3-2). The reading should be 3.6 to 4.5 ounces (100 to 125 grams).
  7. If the readings were low in both directions, remove the brake spring (shown in Fig. 3-3) from the existing anchor hole on the brake lever and install the spring in the next hole located father away from the brake solenoid.
  8. If the readings were high in both directions, move the spring anchor point closer to the brake solenoid.
  9. If the brake spring was moved, repeat steps 2 through 6 to check the results.
  10. Repeat the brake adjustment procedure on the takeup reel. Note that a high braking force is present when the takeup reel is rotated clockwise. The braking force specifications are the same as for the supply reel. Table 3-1 Braking Force Specifications
A3.6 to 4.5 ounces (100 to 125 grams)
B7.9 to 9.7 ounces (225 to 275 grams)
Fig. 3-2 Brake Measurement: the supply and takeup reels side by side, a spring scale hooked into a cord wound round each hub, arrows A and B marking the two pull directions, with the braking force table beside them⤢ zoomFig. 3-2 Brake Measurement: the supply and takeup reels side by side, a spring scale hooked into a cord wound round each hub, arrows A and B marking the two pull directions, with the braking force table beside them

Fig. 3-3 Brake Assembly Location: the brake assembly: brake drum, band and band guide, the solenoid at the left, the cushion above, and the two hexagonal socket-head screws⤢ zoomFig. 3-3 Brake Assembly Location: the brake assembly: brake drum, band and band guide, the solenoid at the left, the cushion above, and the two hexagonal socket-head screws

CAPSTAN PINCH ROLLER PRESSURE ADJUSTMENT

The capstan pinch roller's pressure against the capstan is determined by the capstan solenoid spring. This force is adjusted by means of the nut shown in Fig. 3-5. The nut is adjusted to obtain a force of 6.4~7.0 pounds. The resistance of the solenoid coil rises with the temperature and causes the solenoid's force to decrease. Therefore, do not adjust the pinch roller's pressure until the recorder has been operated in the play mode for at least 30 minutes. The following procedure should be adhered to.

Fig. 3-5 Pinch Roller Pressure Adjustment: the pinch roller arm and capstan solenoid linkage, with the lock nut and pressure nut identified at the bottom⤢ zoomFig. 3-5 Pinch Roller Pressure Adjustment: the pinch roller arm and capstan solenoid linkage, with the lock nut and pressure nut identified at the bottom

  1. Use adhesive tape to hold the takeup-tension-arm safety switch in an upright position so that the safety switch is not activated.
  2. Tie a length of cord or twine together to form a continuous loop. Place one end of the loop around the capstan pinch roller shaft.
  3. Press the PLAY pushbutton. The pinch roller will move to make contact with the capstan and both will rotate.
  4. Hook a 0 to 10 pound spring scale to the other end of the cord and pull the cord taut, straight to the center of the capstan as is shown in Fig. 3-4. Do not let the cord come into contact with the rotating pinch roller.

Fig. 3-4 Pinch Roller Pressure Measurement: a spring scale pulling a cord looped round the pinch roller, away from the capstan shaft below it⤢ zoomFig. 3-4 Pinch Roller Pressure Measurement: a spring scale pulling a cord looped round the pinch roller, away from the capstan shaft below it

  1. Pull on the scale and note the scale reading when the pinch roller just loses contact with the capstan (the pinch roller stops rotating). The scale reading should be 6.4 ~ 7.0 pounds.
  2. If a proper scale reading was not obtained in step 5, loosen the locknut and adjust the pressure nut as required. (Turning the pressure nut towards the spring increases pinch roller pressure.) Tighten the locknut.
  3. After adjustment has been completed, check that the solenoid bottoms within the solenoid coil (the pinch roller can easily be pushed away from the capstan). If the solenoid does not bottom, loosen the locknut and turn the pressure nut away from the spring until the solenoid bottoms. Recheck the pressure adjustment and tighten the locknut. SPRING SCALE

PINCH ROLLER

CAPSTAN SHAFT

Fig. 3-4 Pinch Roller Pressure Measurement

CAPSTAN SOLENOID

PINCH ROLLER

LOCK NUT

PRESSURE NUT

Fig. 3-5 Pinch Roller Pressure Adjustment

CAPSTAN SPEED ADJUSTMENT

The capstan speed can only be adjusted on the dc servo capstan motor, by using the speed adjustment controls on the servo control p.c.b.

This adjustment follows the tape speed measurement in Section 4, and the speed control shown in Fig. 3-6 is adjusted as necessary.

Fig. 3-6 Capstan Servo Control P.C.B.

L : 3 3/4 ips M : 7 1/2 ips H : 15 ips

Fig. 3-6 Capstan Servo Control P.C.B.: the capstan servo control board with its L, M and H speed trimmers, noted as 3¾, 7½ and 15 ips⤢ zoomFig. 3-6 Capstan Servo Control P.C.B.: the capstan servo control board with its L, M and H speed trimmers, noted as 3¾, 7½ and 15 ips

3-5 TAPE TRANSPORT TIMING CHART↑ TOP

Fig. 3-7 Control Timing Chart: a timing chart of the transport commands against relay and motor states through play, record, edit, punch-in and punch-out⤢ zoomFig. 3-7 Control Timing Chart: a timing chart of the transport commands against relay and motor states through play, record, edit, punch-in and punch-out

3-6 RECORDING PROCESS TIMING CHART↑ TOP

REC. COMMAND CN R-2

REC. RELAY (RL301/401)

REC. BIAS (T501-7)

REC. AUDIO SIGNAL (IC301-5/401-5)

t1 t2 t3 t4 t5 t6 RECORDING

t1 : Rec. relay operate time ; 7 to 20 msec t2 : Rec. bias start delay time ; 30 msec t3 : Rec. bias rise time (95%) ; 350 msec t4 : Rec. bias fall time ; 40 msec t5 : Rec. relay release delay time ; 230 msec t6 : Rec. signal muting delay time ; 300 msec

Fig. 3-8 Recording Process Timing Chart

Fig. 3-8 Recording Process Timing Chart: a timing chart of the record command, relay, bias and audio signal traces, with intervals t1 to t6 and their times listed below⤢ zoomFig. 3-8 Recording Process Timing Chart: a timing chart of the record command, relay, bias and audio signal traces, with intervals t1 to t6 and their times listed below

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