Sherwood RX-772, Service Manual

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Ref No.
Power On Failure A) AC-Cord check.
1. FLT does not light up. B) Power Trans (Main/ST-BY) check.
2. ST-BY LED does not light up. C) Fuse's disconnection check. F 501
D) Connector's disconnection or disjunction. CP(500, 503)
Change or close insertion of the connector. FPC101
E) Inferior ST-By switch. SW501
Fuse Disconnection. A) Inferior transformer.
(Power On) B) AMP drive transistor out. (POWER TR) Q306(L, R), Q307 ( L, R )
C) voltage check.
1. B+ ( 55 )V, B- ( 55 ) V
Key Disorder. A) Key's being pushed check.
B) Key signal input components inferior.
C) Key data check. I.C201 Pin No. ( 49 )
D)
μ
-COM I.C201 or Resonator inferior.
1.
μ
-COM IC B+( 5 )V check.
I.C Pin No. ( 15, 16 )
2.
μ
-COM clock pulse check. I.C Pin No. ( 10, 11 )
Power Off in 2~3 sec. A) Regulator I.C out.
after Power On. 1. Signal IN/OUT check.
B) Drive transistor out. ( POWER TR ) Q306 ( L, R ), Q307(L, R)
C) Protection circuit check.
1. Output DC check. Q512
2.
μ
-COM I.C protection terminal check.
u-COM IC201 Pin No. ( 1 )
3. Posistor's disconnection check. CP507
D) Connector's disconnection or disjunction CP502
E) SLEEP MODE cancellation.
Bump Sound A) SPK Mute transistor's out and inferior. Q ( 316L, 316R , 318L, 318R)
(During input-select switch's change.)
μ
-Com front mute control PORT check.
IC201 Pin No. ( 28 )
Sounds from Speaker when A) HEADPHONE JACK connection inferior. JK302
Headphone's connected. B) IC 201(µ-Com) inferior.
1. IC201 H/P RLY control "PORT" check. Pin No. (5)
Bass / Treble Control Failure. A) VOLUME I.C check.
1. Capacitor correction figure check. C(135L, 135R, 154L, 154R)
C(136L, 136R)
2. Signal IN/OUT terminal check.
3. I.C104 voltage check. ( +6.8 )V, ( -6.8 )V I.C PIN No. ( 37, 38 )
4. I.C104 CLK/DATA I.C PIN No. ( 15, 14 )
TROUBLESHOOTING
Cause and Remedy Symptom