Rotel RA 310 Service Manual

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RDTEU

SERVICE MANUAL
RA-31O Pre-Main Stereo Amplifier

- Roland Electronics Co.. Ltd.-

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ALIGNMENT PROCEDURE

PRECAUTIONS

1. Always disconnect the chassis from power line when soldering. Turning the
power switch OFF is not enough. Power line leakage passing through the
heating element may destroy the transistors.

2. Never attempt to do any work on the transistor amplifiers without first
disconnecting the AC line cord and waiting until the power supply filter
capacitors have discharged.

3. Replacement for output and driver transistors, if necessary, must be made
from the same beta group as the orignal type.

4. If one output transistor burns out (open or short) always remove all the
output transistors in that channel and check the bias adjustment, the control
and other parts in the network with an ohm-meter before inserting a new
transistor. All transistors in one channel will be destroyed if the base biasing
circuit is open on the emitter end.

5. When mounting a replacement power transistor, be sure that the bottom of
the flange. the mica insulators and the surface of the heat sink are free of
foreign matter. for they may cause transistors failure.

6. Silicon grease must be applied between the transistor and the mica insulator,
and between the mica insulator and the heat sink for better heat conduction.

PREDRIVER/DRIVER ADJUSTMENT

1. Set BALANCE, BASS and TREBLE controls to their center position.

2. Set MODE switch to STEREO", SPEAKER switch to "ON" and SELEC-
TOR switch to AUX" position.

3. Connect an 8 ohm. 50-watt resistor across L speaker terminalsln parallel
with the load resistor. connect the vertical input leads from the oscilloscope.

4. Connect an audio generator. set for 1,000 Hz (sine wave), to L chan. AUX
input.

5. Connect the AC power cord and rotate the volume control to clockwise
position, to full volume. Increase the generator output until the sine wave
on the scope just starts clipping. Adjust the DC balance, VR701, for equal
clipping on the positive and negative half cycles of the signal. (Fig. 1)

7.

Rotate the volume control to counter-clockwise position, to achieve 0.1
watt (0.9 volt RMS, 8 ohm) Output. To adjust for crossover distortion,
adjust the VR702 until the crossover is extinguished. Or, adjust idling
current using a DCmV meter, across R716 resistor on "AF-17 driver
board and rotate VR702 to obtain a 10 mV reading on the DCmV meter
(no signal input).

Repeat the preceding steps for the right channel.

Fig. 1 DC Balance Adjustment

or l:>

Fig. 2 Crossover Distortion Adjustment

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ENTIRE UNIT INOPERATIVE
I.

If the pilot lamp does not light

A. Check to see if the AC Power Supply Cord is properly connected to
the power source.

B. Check to see if there is adequate voltage from the power source.
C. If A & B are OK, check to see if the AC fuse is not blown.
1. If the AC fuse is OK,

a. AC Power Supply Cord is cut. or
b. Primary Winding in the Power Transformer is cut, or
c. Power Switch connection is faulty.

2. If the AC fuse is blown,
a. Primary Winding in the Power Transformer is shorted out, or
b. Secondary Winding in the Power Transformer is shorted out, or
c. Rectifier (D901 = 181850) is shorted out.