PHILIPS L04EAA CHASSIS
Manual de Servicio

EN 76

9.

L04E AA

Circuit Descriptions, List of Abbreviations, and IC Data Sheets
EHT_info The �PHI2 correction� is to correct the storage time deviation of the Line Output Transistor, which is causing geometry distortion due to brightness change. Line EHT_info is to correct the geometry distortion due to EHT deviation. Both of them feedback through the EHTO and PH2LF pin, and correct the geometry through the East-West circuit. Power Down The power down connection is for EHT discharge during AC Power �Off� state. In the Hercules, if EHT_info > 3.9 V, it will trigger the X-ray protection circuit via a 2fH soft stop sequence. The Hercules bits OSO (Switch Off in Vertical Over scan) and FBC (Fixed Beam Current Switch Off) will discharge the EHT with 1mA cathode current at over-scan position. During switch-off, the H_out frequency is doubled immediately and the duty cycle is set to 25% fixed, during 43 ms. The RGB outputs are driven �high� to get a controlled discharge of the picture tube with 1 mA during 38 ms. This will decrease the EHT to about half the nominal value (= safety requirement). When bit OSO is set, the white spot/flash during switch-off will be written in overscan and thus will not be visible on the screen. Careful application must guarantee that the vertical deflection stays operational until the end of the discharge period. 9.3.5 DAF The Dynamic Astigmatic Focus (DAF) circuit is required by 34RF sets only. It provides vertical DAF and horizontal DAF. Both of the parabola signals are derived through integration by using chassis available signals: � The vertical parabola is using RC integration (via R3403 and C2401) on the Frame sensing resistor saw tooth (Frame_FB). The horizontal parabola is obtained by 2 RC integration (R3409, R3410, C2402, C2403) on the +9V LOT output. Both of the parabolas are added on the output stage through adder TS7402 and TS7403. The collector of TS7402 emitterdrives TS7401 and is amplified by pull up resistor R3411. D6401 and C2405 provide the rectified supply voltage. 9.3.6 X-ray Protection The X-ray protection circuit rectifies the filament voltage and uses it to trigger TS7481 when the EHT is too high. TS7481 is biased at �off� condition by D6480, R3482, and R3483 during normal operation. When the EHT goes too high, the voltage across R3482 will tend to increase as well, while the voltage across D6481 is fixed. Up to certain level (triggering point), TS7481 will be �on� and will force the EHT_info > 3.9 V. The chassis will be shut down through a soft stop sequence. 9.3.7 Vertical Deflection The Frame stage consists fully of discrete components. This has the advantage for better flash behavior than when an IC was used. The Frame differential drive signal from the Hercules comes from a current source. Resistors R3460 and R3461 convert them into a voltage, and feed them into the differential amplifier TS7455 and TS7456. The output of TS7456 is input to the next amplification stage of TS7452. Finally, TS7451 and TS7453 deliver the Vertical yoke current to the coil and feedback through the sensing resistors R3471 and R3472. D6458 and TS7454 are used to bias TS7451 and TS7453, to get rid of zero crossovers, which can cause horizontal lines at the screen center. The negative supply is from -12V and the positive scanning supply is from +12V through D6459. The flyback supply is derived from D6455, D6456 and C2456. This circuit is a voltage doubler, which stores energy in C2456 during the Line flyback �

Panorama For Wide Screen sets, the S-correction of the picture has to adapt between the different picture modes. In particular, between 16:9 Wide Screen and 4:3 picture modes. This is achieved with the (separate) Panorama circuit (see diagram �G�). A signal (I2SDI1) from the UOC controls the state of TS7463. When in the normal 16:9 Wide Screen mode, the signal is �low� and therefore TS7463 is switched �off�. When the 4:3 mode is selected, this signal from the UOC is pulled �high�, switching TS7463 �on�. The relay 1463 on the Panorama panel is subsequently turned �on� and, in effect, paralleling capacitor C2475/C2474 to the S-Cap C2469/ C2470. This changes the overall effective S-correction. The relay is switched �on� in 4:3 and Superwide picture modes. 9.3.3 Auxiliary Voltages The horizontal deflection provides various auxiliary voltages derived either directly or indirectly from the secondary pins of the LOT: � +9V: This supplies the Hercules�s flyback driver. � � � � � +11V: This supplies the frame amplifier. -12V: This supplies the frame amplifier. 50V: This supplies the frame amplifier. Filament: This supplies the heater pins of the picture tube. VideoSupply (+200V from primary side of LOT): This supplies the RGB amplifier and Scavem circuit at the CRT panel.

Notes: � The V_T voltage (to tuner) is drawn from V_batt. � The EHT voltage is generated by the Line Output Transformer (LOT). The Focus and Vg2 voltages are created with two potentiometers integrated in the transformer. 9.3.4 Beam Current The beam current is adjusted with R3451 and R3452. The components R3473, R3453 and C2451 determine the EHT_info characteristic. The voltage across C2412 varies when the beam current changes. This EHT_info is used to compensate the picture geometry via pin 97 of the Hercules when the picture changes rapidly, and compensate the phase 2 loop via pin 113 of the Hercules. Also from the EHT_info line, a BCL signal is derived and sent to the Hercules for controlling the picture�s contrast and brightness. When the picture content becomes brighter, it will introduce: � Geometry distortion due to the impedance of the LOT causing the EHT to drop. � Picture blooming due to the picture characteristics Because of the above mentioned, we will need a circuit for Beam Current Limiter (BCL) and EHT compensation (EHT_info). These two circuits derive the signal from the picture tube current info through LOT pin 10. BCL � When the BCL pin voltage goes to 2.8 V, the Hercules will start to limit CONTRAST gain. � When it reaches 1.7 V, then the BRIGHTNESS gain limit will start to react. � When BCL pin voltage goes to 0.8 V, the RGB will be blanked. Components TS7483, R3490, R3491, R3492, and C2483 are for fast beam current limiting (e.g. with a Black-to-White pattern). Components R3454, D6451, D6450, C2453, R3493, and C2230 are for average beam current limiting. C2453 and R3493 also control the timing where average beam current limiting is more active or less active.