Aiwa CX-NAK772, Service Manual

Page: 4 / 46

NOTE ON BEFORE STARTING REPAIR
Fig-1
MAIN C.B
D101
C101 C102
2 2
3 4
Charging voltage (V) Discharging
Rated power (W) Parts number
(C101, 102) resistor (ohm)
25-48 100 3 87-A00-247-090
49-140 220 5 87-A00-232-090
1. Forced discharge of electrolytic capacitor of power supply block
When repair is going to be attempted in the set that uses relay circuit in the power supply block, electric potential is kept
charged across the electrolytic capacitors (C101, 102) even though AC power cord is removed. If repair is attempted in this
condition, the secondary defect can occur.
In order to prevent the secondary trouble, perform the following measures before starting repair work.
Discharge procedure
1
Remove the AC power cord.
2
Connect a discharging resistor at an end of lead
wire that has clips at both ends. Connector the
other end of the lead wire to metal chassis.
3
Contact the other end of the discharging resistor
to the positive (+) side (+VH) of C101. (For two
seconds)
4
Contact the same end of the discharging resistor
as step
3
to the negative (-) side (-VH) of C102
in the same way. (For two seconds)
5
Check that voltage across C101 and C102 has
decreased 1 V or less using a multimeter or an
oscilloscope.
Select a discharging resistor referring to the following table.
Note: The reference numbers (C101, C102) of the electrolytic capacitors can change depending on the models. Be sure to check
the reference numbers of the charging capacitor on schematic diagram before starting the discharging work.
2. Check items before exchanging the MICROCOMPUTER
Be sure to check the following items before exchanging the MICROCOMPUTER. Exchange the MICROCOMPUTER after
confirming that the MICROCOMPUTER is surely defective.
2-1. Regarding the HOLD terminal of the MICROCOMPUTER
When the HOLD terminal (INPUT) of the MICROCOMPUTER is “H”, the MICROCOMPUTER is judged to be
operating correctly. When this terminal is “L”, the main power cannot be turned on. Therefore, be sure to check the
terminal voltage of the HOLD terminal before exchange.
When the MICROCOMPUTER is not defective, the HOLD terminal can also go “L” when the POWER AMPLIFIER
has any abnormalities that triggers the abnormality detection circuit on the MAIN C. B. that sets the HOLD terminal to
“L”.
• Good or no good judgment of the MICROCOMPUTER
1
Turn on the AC main power.
2
Confirm that the main power is turned on and the HOLD terminal of the MICROCOMPUTER keeps the “H”
level or not.
3
When the HOLD terminal is “L” level, the abnormality detection circuit is judged to be working correctly and
the MICROCOMPUTER is judged to be good.
4
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