Troubleshooting - Sherwood RD-7502 Service Manual

Symptom
Power On Failure
1. FLT does not light up.
2. ST-BY LED does not light up.
Fuse Disconnection.
(Power On)
Key Disorder.
Power Off in 2~3 sec.
after Power On.
Bump Sound
(During input-select switch's change.)
Sounds from Speaker when
Head phone's connected.
Bass / Treble Control Failure.

TROUBLESHOOTING

Cause and Remedy
A) AC-Cord check.
B) Power Trans (Main/ST-BY) check.
C) Fuse's disconnection check.
D) Connector's disconnection or disjunction.
Change or close insertion of the connector.
E) Inferior ST-By switch.
F) VFD Driver I.C & Resonator check.
1. VFD Driver I.C VCC(+3.3)V check.
2. VFD Driver clock pulse check.
A) Inferior transformer.
B) AMP drive TR out. (POWER TR)
C) AMP drive TR out. ( POWER TR )
D) voltage check.
1. B+ ( 40 )V, B- ( 40 ) V
A) Key's being pushed check.
B) Key signal input components inferior.
C) Key data check.
D) µ-COM I.C or Resonator inferior.
1. µ-COM IC VCC +3.3V check.
2. µ-COM clock pulse check.
A) Regulator I.C out.
1. Signal IN/OUT check.
B) Drive transistor out. ( POWER TR )
C) Protection circuit check.
1. Output DC check.
2. µ-COM I.C protection terminal check.
D) Connector's disconnection or disjunction
E) SLEEP MODE cancellation.
A) FRONT Mute transistor's out and inferior.
µ-Com front mute control PORT check.
B) CENTER Mute transistor's out and inferior.
µ-Com center mute control PORT check.
C) SURROUND Mute transistor's out and inferior.
µ-Com surround mute control PORT check.
D) SURROUND BACK Mute transistor's out and inferior.
µ-Com surround mute control PORT check.
A) HEADPHONE JACK connection inferior.
A) Bass volume check.
1. Resister/Capacitor correction figure check.
2. BASS VR's property inferior.
18
Ref No.
F ( 300,301)
CN301,CP514
SW(700)
I.C701 SC16315
I.C701 Pin No13
I.C701 Pin No5
Q206( FL, FR, C, SL, SR, SBL, SBR )
Q205 ( FL, FR, C, SL, SR, SBL, SBR )
SW ( 700 )
I.C402 Pin No. ( 38,39,40 )
I.C402 Pin No. ( 23,35,36,84 )
I.C402 Pin No. ( 82,83 )
I.C 300 (LM1117S_3.3V)
Q205 ( FL, FR, C, SL, SR, SBL, SBR )
Q206 ( FL, FR, C, SL, SR, SBL, SBR )
u-COM Pin No. ( 76 )
CP (411)
Q ( 511 )
IC501 Pin No. ( 30 )
Q ( 509 )
IC501 Pin No. ( 29 )
Q ( 510 )
IC501 Pin No. ( 26 )
Q ( 507 )
IC501 Pin No. ( 25 )
CN702
I.C401
I.C401 PIN No. ( 13,14)