Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV set2 Basic boardThis main heading covers the analoguestages from the power supply circuit throughthe power output stages to beam current limitation,irrespective of whether or not they arecontained on the basic board. In order tomaintain consistency, several smaller stageson the basic board are also described.2.1 Standby power supplyThe Q 2500 receiver once again contains astandby power supply circuit, thus limiting currentconsumption in this mode to < 2 Watt.The use of a new CCU SDA 6000 on the signalboard increases the standby power consumptionfrom 1 W to 2 W, compared to theolder model. To meet the requirements of increasedpower consumption, there is now asmall, blocking oscillator type power supplyattached to the operating control, which suppliesthe U5 SB.Siemens Corporation has announced a newindex of the SDA 6000, that needs only 1 Wpower in standby operation. This will be implementedon the signal board, but thestandby power supply will not be changed.mode. All of this contributes to the standbymode’s low power consumption.2.1.1 Standby power supply circuitThe main voltage is fed via W 8103 the switchS 8101 and W 8611 to the basic board andcontinues via the line filter (C 612, T612,C613) and the 3-pole pin connector W613/BBback to pin 2/3 of operating control W 8613.The 220V is rectified by the bridge rectifier D8133 and smoothed by C 8133. The blockingoscillator type power supply consists essentiallyof the control circuit I 8131, in which theswitching transistor for the primary blockingoscillator winding is integrated, the transformerT 8101 and the opto-coupler I 8122. Anoperating voltage of about 18V is led fromwinding T 8101 pin1/2 via D 8138/D 8131 andC 8132 to I 8131 on pin 4. Control input I 8131pin 3 is supplied with secondary side currentcontrol information by opto-coupler I8122.This control circuit stabilises the secondaryside output voltage derived from the windingpin 5/8 of T 8101 at 5V. This is then fed via W8181 pin 8 to the signal board. I8122 is fittedwith an internal excess temperature, excesscurrent and excess voltage switch protection.The blocking oscillator type power supply operatesat a switching frequency of about 50kHz.The circuit itself is mounted together with theIR receiver and the LEDs on its printed circuitboard. It supplies the U5 SB, which maintainsfunctioning of the IR detector, the processorcircuit and the operating software. The lasttwo circuits operate in standby mode, i.e. theclock frequency is reduced internally so thatonly those stages required to recognize aswitch-on command are maintained in operation.Because of the NexTView function with U3.3 the TV RAM is retained in self refreshDocument Q 2500 12 © Loewe ProCollege