Pioneer M-790 Service Manual - Page 19
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M-790
5. ADJUSTMENTS
POWER AMP. UNIT SECTION (Refer to Fig. 1.)
5.1 Handling Precautions
@ Since the heat sink and transistor metallic parts are connected to
the Front Amp output, make sure they do not contact the GND
(chassis) or other circuits.
@ Since there is residual high voltage in the Power Amp Module
Assy +B] (FRONT ASSY) and +B2 (REAR ASSY) even when
the power is OFF, caution should be exercised. (If necessary, the
voltage should be discharged).
@ When handling the Power Amp. UNIT, make sure you do not
touch the fan motor blade.
CAUTION :
5.2 Adjustment and Confirmation of Idle Current
@ Basically, the idle current needs to be confirmed when replacing
a power transistor, driver transistor, or bias transistor, or when
the entire split board Assy of the Power Amp. UNIT has been
replaced.
@ Make sure the heat sink has cooled sufficiently before measuring
the idle current. (Temperature should be the same as room tem-
perature; 25°C is ideal, if possible.)
@ Idle current stipulated value: 3 - 5OmA.
Before performing this adjustment, short the blow trigger shorting pin (shown in Fig. 2) of the FRONT ASSY to prevent the protection
IC from malfunction. After adjustment is completed, remove the short-circuit.
@ Front Amp Side (FRONT ASSY)
Rch side
following procedure.
| Measurement |
tem
Short both sides of C7123 and C7124 on the Rear Amp side.
Do not operate the Rear Amp side.
Lch side
Insert a resistor (0.22Q, 3W or more) in series in the connector
CN7502 +B1 (or —B1) line (terminal No.5 or 6). (Refer to Fig.3)
Short both sides of C7524.
Do not operate Rch side.
Tum oe power ON, wait 6 seconds, and then measure the resistance
Leh Idle current 1=V/0.22 (Q)
voltage in Step 2.
@ Same as Steps | and 2 above.
,
@ Short both sides of C7523,
Do not operate Lh side.
Tum the power ON under the above conditions, and after 6 seconds
measure the resistance voltage in Step 2.
If the measured idle current is greater than S0mA, perform the
For measuring voltage at both sides of
resistor.
confirm that it is below SOmA.
Short between the Point @) pattern in Fig.4 using solder.
Short between the Point ® pattern in Fig.4 using solder.
26
If the idle current is below 3mA, perform the following procedure.
Short between the Point © pattern in Fig.4 using solder.
Short between the Point © pattern in Fig.4 using solder.
Connect R7517 to R7515 in a parallel
circuit.
Connect R7518 to R7516 in a parallel
circuit.
Connect R7551 to R7519 in a parallel
circuit.
Connect R7552 to R7520 in a parallel
circuit.