Pioneer XRP-440-M Service manual

No.: SK49006
Date: JAN,25, 1995

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XR-P740M,740,640M,640,440M,440
340M,340
XR-J25M,22M,22,15M,11M,11

SX-J320,420,520,720
RX-P840,570,570S,J33,370
M-770

THE CIRCUIT OPERATION OF THE POWER AMP MODULE

Fig-1&2: THE BLOCK DIAGRAM OF POWER MODULE PROTECTION CIRCUIT

Page-1 : 1.THE PRECAUTION IN REPAIRING A SET
Page-2 : THE BLOCK DIAGRAM OF THE PROTECTION CIRCUIT
Page-3 : 2.THE CIRCUIT OPERATION OF THE DETECTORS

3.THE OPERATION OF THE FAN MOTOR
Page-4 : 4.TROUBLE SHOOTING
Page-6 : 5.HOW TO CHECK THE DETECTION CIRCUIT

1. PRECAUTION IN REPAIRING A SET

a. A heat sink for the power transistors should be isolated from
the ground.
A collector of the transistor is directly connected to the heat
sink.

b. A heat sink should be firmly installed onto the power
transistors when checking the circuit, otherwise the transistor

will get damaged or burn out due to thermal runaway.

c. If the AC socket remains plugged into the outlet and power is
in STAND-BY mode,then B1 ±50V and B2 ±25v are still being
supplied.

d. The potential at B1 and B2 on the power module circuit remains
high although the AC socket is unplugged.
Discharge the potential by shorting smoother capacitors C1001
and C1002 on ±50V and C1005 and C1006 on ±25V lines if
transistors and other components on the power module amp. are
to be checked.

PIONEER ELECTRONIC CORPORATION

Issued by

Y.IMAMIZU, Manager
H.E Engineering Sect., Service Dev.

Page-1

"BLOCK DIAGRAM OF THE PROTECTION CIRCUIT"

1.
OUTPUT DC
DETECTION

IS CIRCUIT
ABNORMAL?

ABNORMAL

2.
OVER LOAD
DETECTION

SWITCHING MUTE ON
MUTE CIRCUIT ON

YES

3.
THERMAL
DETECTION

NO

NORMAL
OPERATION

4.
POWER SUPPLY
DETECTION

NORMAL
OPERATION

YES

IS FAULT
ELIMINATED?

NO

ACTIVATING FUSE
BLOW CIRCUIT

BLOWING PRIMARY
FUSE

Page-2

2.THE CIRCUIT OPERATION OF THE DETECTORS

a.DC detector: A circuit operates when neutral voltage at speaker
output exceeds DC ±3V.

b.Over load : Power supply ±11V for the amp IC7501 is ceased
detector and the signal is muted when speaker terminals are
shorted.

*An over load detector does not blow a fuse.
A circuit keeps muting on as long as speakers
are shorted.

c.Thermal : A circuit operates when temperature on a heat sink
detector exceeds 105 degree c.

d.Power : A fuse blow circuit operates when neutral point of
supply the power supply voltage ±12V, ±25V, ±5.6V or
±12V line exceeds ±0.6V. A fuse is blown
immediately without switching mute circuit on.

*In case of detecting DC voltage at speaker output, an over load
current or excessive heat on a heat sink, the amp circuit is
muted by stopping supply of ±11V for an amp IC7501 for two
seconds.
If the detection signal is eliminated during muting on, the
circuit resumes normal operation, but if the detection circuit
keeps on, a fuse is immediately blown.

*In case of detecting abnormal power supply, a fuse is immediately
blown.

3.THE OPERATION OF THE FAN MOTOR

a.Condition of the fan motor rotating at high speed.

1.A speaker output voltage exceeds 3.8V p-p regardless of loading
speakers or headphone.
*Position of the main volume is around 10 o'clock.

2.Temperature on heat sink exceeds 95 degree c.
*Rotating at high speed caused by detecting thermal detector
hardly occurs.



b.Condition of the fan motor rotating at low speed.

1.Temperature on a heat sink exceeds 85 degree c.

2.Function is CD or DECK and in playing.

*The fan motor stops when temperature decreases to 75 degree c.

Page-3