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High Voltage Control Circuit:
High Voltage Control Circuit is working basically by using switching theory with the main component
ICF01 (KA3843). Circuit operating theory is explained as following:
* Refer to the Schemathics in the Page 63 (Schematic Diagram 4-4)
1) When Power ON and the Vcc DC level of pin7 of ICF01 (KA3843) exceeding 8.4V, ICF01 starts
to work and the oscillate frequency is decided by RF04, CF04.
2) When ICH2 is working normally the output square wave of pin6 will turn on QF01. The
ON/OFF cycle of QF01 will make the primary of FBT(pin 1~2) acted like a Switching Power
X'FMR.
3) AFC signal is differential by CF05, RF06 and connected with CF04 in order to force ICF01 in
synchronization. Then, the high voltage will be always synchronized with horizontal deflection.
4) Usually loading change will cause unstable condition, so a high voltage feed back system is
designed to maintain the stability of the high voltage circuit. This feed back system is started from
voltage sensor on the pin12 of the FBT. This sensor voltage compares with voltage of the
OP1 via the buffer(OP2) of LM358 and returns to ICF01.
LM358 OP1 is controlled by following factors:
1) A feed back reference high voltage circuit that consists of RF21,VRF01 and RF20 to adjust
the high voltage.
2) During the period the horizontal frequency is changed, for example, H-UnLock will be from
low to high (the time frequency changes). H-Unlock is controlled by pin 17 (H-UnLock) of
ICH01 TDA4841. After differential circuit that consists of RF17 and RF18, the signal will turn
QF03 on when frequency changed and reduce the high voltage by paralleling with
RF21,VRF01 and RF20.
X-RAY High Voltage Protection CRT
X-RAY High Voltage Protection CRT is to get a DC level voltage by utilizing the output waveform of
FBT's pin4 to pin9(GND) via a rectifier consists of DH18, CH45. This DC level voltage inputs to the pin2
(X-RAY) of ICH01 TDA4841 The preset X-RAY protection voltage is 6.3V. If the high voltage is higher
than the preset voltage, the DC level voltage input into the pin2 will also be higher than 6.3V.
It also means the HD signal is off, then horizontal deflection is off and the high voltage is also off.
Video-Amplifier/On-Screen-Display
The video amplifier system is consist of the Pre-Amplifier, the Video-Power-Amplifier, and the Cutoff-
Voltage-Adjusting circuits.
The functions of the Pre-Amplifier ICC01(KA2506) include:
* Refer to the Schemathics in the Page 62 (Schematic Diagram 4-3)
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