3. Excessive Anode Current Protector Circuit
The excessive anode current protector circuit is installed in this model for the purpose of protecting CRT
when an excessive anode current flows through the CRT due to failure of the current limiting circuitOs
(ABL circuitOs) voltage detection system and control system. The excessive anode current protector
circuit consists of IC502 (1/2), D901, D512, D513 and their peripheral circuit components. The anode
current is monitored in the form of voltage level as the anode current flowing through the high voltage
coil of FBT is converted from current to voltage by R804 of the PC board.
The voltage difference between the converted voltage and the reference voltage D901, is divided by the
resistance-type-voltage-divider R514 and R515, and is sent to the positive (+) terminal of the comparator
IC502 (1/2). At the same time, the reference voltage D901 is divided by the resistance-type-voltage-
divider R518, R522 and R517, and is applied to the negative (-) input terminal as the protector operating
voltage. As the anode current flows, the converted voltage decreases and the input voltage to the positive
(+) input terminal decreases and the current decreases.
As long as the ABL circuit operates, the positive (+) input terminal remains higher than the negative (-)
input terminal so that the comparator output is kept high.
If the anode current flows due to failure of the ABL circuit and the positive (+) input terminal exceeds the
ABL setting voltage of the comparator and becomes lower than the protector setting voltage, the compar-
ator output goes low. As the result Q501 is turned on through D502. The high voltage converter stops
operating in the same manner as the over-voltage protector so that the high voltage output is held down.
IC501 (1/2) has the latch function with D512 and D513. If the comparator output goes low, the level is
maintained
4. Dynamic Focus Circuit
The DFX signal for the vertical line correction (for X-axis) and the DFY signal for the horizontal line
correction (for Y-axis) are inputted from the E board.
The DFX signal is amplified by Q301, Q302, Q303, Q304 and Q305, and is stepped up by T301. The
DFY signal is amplified by Q321 and Q322.
The amplified DFX and DFY output signals are drive the focus pack so that the GM voltage that is the G4
voltage of CRT is modulated until the optimum focus is obtained over the entire screen.
5. Screen (G2) Voltage Regulator Circuit
The screen regulator circuit consists of IC401 (1/2), Q201 and Q202.
The G2 regulator circuit is controlled by the G2 control voltage that is supplied from the BK board so that
the optimum cathode voltage is obtained.
At the same time, the power supply voltage for this circuit is the high voltage that is obtained by rectify-
ing the drain pulse voltage at Q109.
BVM-D32E1WA/D32E1WE/D32E1WU6-5 |
ACEC
