Pioneer XW-NAV1-K Service Manual page 31

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(5) AC Detection Circuit of Power Supply Part
Overview
Power failure detection circuit of this model does not directly monitor AC voltage.
It monitors AC negative voltage, second part winding transformer input, which is in proportion to DC voltage at first side
smoothing condenser C501, which detects amount of AC input voltage. Even though AC voltage is blocked, it works
normally on condition that C501 voltage is more than regular amount.
Detection Circuit
Regarding second part winding transformer input (before D513 rectification), AC negative volatage is gained by passing
D514.
Normally, because an electric current which exceeds threshold count flows in D515, Q502 turns ON.
Then, "H" is returned to Sub U-CON terminal (POWER_FAIL: IC3001/18 pin), and the situation which live AC voltage from
a wall socket is detected.
When it become AC OFF/power failure, accompanied by AC input voltage, C501 DC voltage gets lowered.
In adttion, AC negative voltage at second part winding transformer input is lowered. When electric current which does not
exceed threshold of D515 and does not flow, electric current does not flow in Q502 base terminal, and it turns OFF.
Because of this, "L" is returned to Sub U-CON terminal, and the situation whitch AC voltage is stopped is detected.
Detection and Return
When POWER_FAIL detection starts, POWER_FAIL terminal of Sub U-CON waits interrupting.
During both STANDBY and P. ON, the situation is discriminated at 4 mSec intervals. Then, when the results are "L" and
the same twice, the fact that AC is stopped is confirmed.
After POWER_FAIL detection, change SYS_POWER-H signal (IC3001/70 pin) to "L", and turn P. CON off.
Afterward, stop main CLOCK (16 MHz)'s oscillatory, and make Sub U-CON wait mode.
This time, only POWER_FAIL terminal gets effective regarding interrupting from outside. (1 Sec timer for backup usage is
TE
L 13942296513
renewed.)
How to return: When POWER_FAIL terminal becomes "H" ten times at 20 mSec intervals, we assume voltage is applied
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