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(4) Output of operating voltage
Refer to the service manual for the schematic diagram.
(i)
Starting the PWM controller
When the function dial is rotated, the XWP signal becomes L, and this is detected by the HI microprocessor (Pin &ª of
IC301). As a result, the mode changes from the sleep mode to the normal mode. (The 4.19 MHz of X301 starts oscillation).
The H output of the 5VON (Pin !¢ of IC301) of the Hi microprocessor is input to the PWM controller (Pin #º of IC004),
and each regulator starts.
(ii) Switching regulator (SWR)
The 5V REG (Q032, Q035), 2.8V REG (Q034, Q038), 5V REG (Q033, Q037), and 3.1V REG (Q031, Q036) are regulators
combining the step-down SWR and step-up SWR. The former stage transistor in each regulator is for step-down, and the latter-
stage is for step-up.
stage is for step-up.
The voltage is regulated according to the UNREG voltage input.
Fig. 4 5V Regulator
(Important) PWM controller protection circuit
The PWM controller (IC004) monitors the operations of each regulator. When faults occur, it stops all circuit operations to
protect the circuits. Consequently, should a fault occur in even one regulator, IC004 will stop all regulator operations. Take
note that this is not a fault of IC004.
note that this is not a fault of IC004.
By setting the SCP terminal (Pin @£ of IC004) to L during the repair of the power supply circuit, the protection circuit will
stop operating, so that the operations of each circuit can be checked. Check which circuit is outputting the abnormal voltage.
(Repair Tips) Differentiating the malfunctioned circuit
The power supply circuit consists of the step-up circuit and step-down circuit. For example, the unit may operate in the AC
adapter but may not operate in a rechargeable battery where the voltage is low.
Therefore, change the voltage supplied from the DC jack, and determine the faulty section.
If voltage cannot be output due to the faulty step-up circuit, check the 8V REG (IC012, etc.) and 5V REG (Q024, etc.).
If voltage cannot be output due to the faulty step-up circuit, check the 8V REG (IC012, etc.) and 5V REG (Q024, etc.).
(iii) Step-down SWR
When the UNREG voltage is higher than the output voltage, only the former-stage step-down SWR operates. The step-down
SWR is controlled by the PWM controller (IC004), and the output voltage is stepped-down by the switching of the IC004
terminal.
terminal.
If the step-down SWR is operating, to cancel the voltage drop by the diode of the latter-stage step-up SWR circuit, the
internal transistor made up of Q035, Q036, Q037, and Q038 is turned ON, and both ends of the diode (Pins 3 and 5 of the
transistor) are short-circuited. (Refer to Fig. 4, Table-2 “Cancel Output”.)
transistor) are short-circuited. (Refer to Fig. 4, Table-2 “Cancel Output”.)
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