Rotel RA 610 Service Manual

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RDTEU

SERVICE MANUAL
RA-61O 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 original type.

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

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

6. Silicon grease must be applied between the transistor and the mica insu.
lator, 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.
Connect 8 ohm BOwatts resistor across L speaker terminals. in parallel

with the load resistor. connect the vertical input leads of the oscillo-

scope.
Connect an audio generator, set for 1,000Hz (sine wave), to Lchan.
AUX input.

Check the DC balance. Connect AC power cord and rotate volume control
to clockwise position, -full volume. Increase generator output until
sine wave on scope just starts clipping, -equal clipping on the posi-

tive and negative half cycles of the signal.

Rotate volume control to counter-clockwise position to get 0.9 volts
RMS 8 ohm (0.1 watts) output. Adjust crossover distortion. adjust VR
505 until the crossover is extinguished. See Fig. 1(A). Or adjust idling
current using a DCmV meter, DCmV meter across R908 resistor on rear
chassis; rotate VR505 to obtain a 15mV reading on DCmV meter (on
signal input). See Fig 1(B).

Repeat preceding steps for right channel.