Repair Introduction; Explanation Of Circuits - Marantz MR2020 Service Manual

2-2. REPAIR INTRODUCTION

PREPARATION FOR CD BLOCK
1. Set a disc for repair into product.
2. Tur n the product upside down on the jig (Parts
No.*MR2021JIG). Take care that the top cover will not
damaged, especially the 4 levers. (Refer to "How to
disassemble MD2020")
3. For the top panel will not open while repairing, remove
the connecting wires of panel motor from the connector
(J812).
4. Repair and operate it on the upside down position of
the product.
PREPARATION FOR MAIN AMPLIFIER PCB (P704)
1. Main amplifier is BTL output.
2. For removing the main amplifier PCB (P704) from the
product, remove the wire (W802) from the terminal
(WU02) of microprocessor PCB (PU04). Connect
another wire with terminal (WU02) and GND as chassis
instead of the wire (W802).
REMARK
Remove the bottom case from the product, Do not output
signals of over 1W from both channels more than 10
minutes continuously.

2-3. EXPLANATION OF CIRCUITS

FAN OPERATION
The voltage added to the diode (D852) is depended on
the resistance of the thermistor (R857) and resistors
(R855,R858). When the temperature of the heat sink
goes up, the resistance of the thermisor (R857)
decreases, and the voltage added to the diode (D852)
increases.
1. When the temperature of the heat sink is over 70
degrees Celsius, then D852 is on, through R852, Q851
is on, and the fan starts to revolve.
2. When the temperature of the heat sink is approx. 100
degrees Celsius or more, through R853, Q853 is on,
and the product is STAND-BY status. But, if the fan
revolve normally, the temperature of the heat sink will
not be over 100 degrees Celsius and not be STAND-
BY status. Therefore, the procedure of the over heat
protection circuit check is as follows;
(1) Connect the test point (J814) with a resistor of 680
ohm.
(2) If the product is STAND-BY status, this circuit is normal.
(3) Remove the resistor of 680 ohm from the test point
(J814).
FAN OPERATION CHECK
Keep outputting 2.5W from both channels of the product.
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