Shure AUDIOMASTER 1200 Service Manual Download

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VR1101 OUTPUT VOLTAGE OFFSET ADJUSTMENT

1. Connect a dc voltmeter between SHR-11 terminal AC and

ground (see Figure 2).

2. Adjust VR1101 so that V1 equals 0 V ±15 mV

VR1102 DRIVER BALANCE ADJUSTMENT

1. Connect a dc voltmeter between CP1101 and ground (see

Figure 2).

2. Adjust VR1102 so that V2 equals 1.2 V.

VR1103 IDLE CURRENT ADJUSTMENT

1. After the unit has been turned on for at least five minutes,

connect a dc voltmeter between R1126 and R1127 as shown
(see Figure 2) and check the idle current. If the value of V3
does not equal 6.6 mV ±3.3 mV, use a razor blade to carefully
remove from the top and side of VR1103 the old cement that
prevented its adjustment from changing.

2. Adjust VR1103 so that V3 equals 6.6 mV ±3.3 mV.
3. Apply a drop of cement (white glue, hot melt glue, caulk, etc.)

to VR1103 to eliminate movement due to vibration.

VR1201 TEMPERATURE SENSOR THRESHOLD ADJUSTMENT

If U1201 or other SHR-12 parts are replaced, VR1201 will

probably require recalibration as follows.

1. Turn off the unit long enough for the heat sink to reach

ambient temperature. Remove all input signal sources and
speaker loads.

2. Measure the heat sink temperature or ambient temperature

around the heat sink. Consult the graph in Figure 3 to
determine the proper voltage at test point CP1402.

3. Attach a dc voltmeter between CP1402 (+) and ground (-).
4. Apply power to the unit and quickly adjust potentiometer

VR1201 on SHR-12 until the proper voltage is reached.

SHR-11 POTENTIOMETER ADJUSTMENTS

FIGURE 2

SHR-12 TEMPERATURE SENSOR BOARD

To remove SHR-12 from the large heat sink, remove the

Power Amplifier Board Assembly from the 1200 as described
above. Then remove the two Phillips screws that hold SHR-12 to
the small vertical heat sink. When replacing SHR-12, U1201
(mounted on the solder side of the board) must physically
contact the vertical heat sink in order to ensure correct opera-

tion of the power amplifier over-temperature protection circuitry.

In addition, apply a small amount of Wakefield Type 120 Thermal
Joint Compound to the top surface of the IC to allow good heat
transfer.

TEMPERATURE SHUTDOWN SENSOR CALIBRATION

FIGURE 3

SHR-14 MAIN BOARD

The 1200 contains four internal fuses mounted on the Main

Board (SHR-14). If replacement becomes necessary, replace
only with identical Normal Blow fuses: two 0.75 A 250 V, and two
8 A 250 V. Do not continue to replace fuses if a fuse continues to
blow; have the trouble corrected.

To remove SHR-14 from the chassis, remove the three Phillips

screws on each of the long sides of the board and the single
screw next to the two 8 A fuses on the short side of the board.

This will allow the board to be lifted free of the chassis. If it is

necessary to completely separate SHR-14 from the 1200,
remove all seven connectors (be sure to label the four 4-pin
connectors and their receptacles to ensure proper reattachment).
Unsolder the six transformer and two fan leads from pins AA

through AH, and the two ground leads connected to Al and AJ.

Be sure to label leads also so they can be resoldered to the
proper pins. Unsolder from connection pins AA and AB of
SHR-11 the red and green wires attached to the solder side of
SHR-14. (Remove cable ties as necessary.) The SHR-14 board
can now be completely detached from the 1200.