Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV set2.3.1 Horizontal driver2.2.9 Servicing informationFor repairs and fault-finding in the power supplyunit the following should be noted:Always connect the unit via an isolation transformer,especially when fault finding the primaryside.The horizontal driver stage is controlled fromI 2521 on the signal board via pin 13 fromconnector W 1511. The pulse at this point is2.5 Vss.U25The load on C 620 remains active long afterthe unit has been switched off. Discharge theload if necessary via a low-resistance resistor.C521!R521T528D532R532T531Q534Operation of the power supply unit without thedigital unit is possible. For this pin 5 on pinconnector W 8181 is connected to earth, butnot until a voltage is applied to the standbypower supply. For specific failures, this testcan also be done with an integrated digitalcomponent.C527 R527C528D527C526R533Basic boardUBA check of the horizontal output stage cannotbe made by withdrawing the deflection plug.For this test L 534 must be unsoldered. Anextra load is not required.R526C524D526Q526A separate test of the power supply unit functionwithout interference from the chassis canbe achieved by unsoldering one side of thesecondary side rectifier diodes. The rectifierbranch for the UB (D 651) and U7 (671) mustbe available. The UB can then be loaded witha 100 Watt LED.U5R1044R2563Q2561R2561R2558R2562Signal boardQ2556 R2557HQ2951DEFLECTIONI 2521Video /deflectionprocessor879I 2801CCUU 7 and UB are necessary for power supplycontrol, so do not deactivate them.U52.3 Horizontal deflection and highvoltage productionOn the 100 Hz Chassis Q 2500 the horizontaldriver, horizontal output stage and high voltageproduction are essentially the same asthe predecessor.Capacitive control via C 524 prevents driverstage Q 526 being held conductive continuouslyif components are faulty or there are nocontrol pulses. Diode D 526 enables rapiddischarge of C 524, if Q 526 is controlled inthe blocking phase.Document Q 2500 21 © Loewe ProCollege