Canon Canovision8 E50E Service Manual page 172

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5. Protection Circuit
When the voltage is applied to the primary circuit excessively, the voltage at pin 8 of IC51 goes
high to operate the latch circuit, end then the PWM signa? is stopped to be outputted.
To detect the excessive current, the current of primary circuit is converted into voltage by R8 and
9. {This voltage has the negative potential to ground.) It is fed to pin 18 of [C51 for detection,
For example, if the secondary circuit's output termina? is shorted and the excessive current appears,
the circuit is protected in the following manners.
Output terminal of secondary circuit shorted > Voltage at secondary circuit dropped + Emission of PHC1
photodiode stopped > Duty ratio of PWM output at pin 2 of ICST increased > Current of primary side
increased + Potential between R8, 9 and ground increased > Excessive current'is detected at pin 18 of
151 (negative potential) > Latch circuit in 1C51 operated > PWM output stopped.
To reset the latch circuit operation, remove the causes (ex. shorting) of failure and emit the charge
mainly at C7 fully by unplugging the power supply and leave it for 1 minute approximately.
Also, to protect the circuit from defective parts, F1 and TF21 (temperature fuse) are installed
ISECONDARY'
RECTIFIER
CIRCUIT
Chapter [J] Adjustment
1. Qutput voltage adjustment
M, EQ. Digital voltmeter
T.P. Refer to Fig. 5
6.8 40.10
* Note: Preform the adjustment without charges.
(1) Remove the cover and the external shield
case.
{2) Connect (+} and (-) terminals of digital
vottmeter to {+) and {-) on C.B.A.
respectively.
(3) Adjust the voltage to 6.8 20.1V.
Fig. 5