Zenith R50V26 Service Manual

Also see for R50V26: Operating guide

Contents

Zenith R50V26 Service Manual Manual pdf 30 page image

CIRCUIT DESCRIPTIONSPV154 - 923-03506 3-6 ZP26/28 - SERVICINGB+ GENERATION FOR SUB POWER SUPPLY DRIVERVcc for the Driver IC is first generated by the AC input.This voltage is called Start Up Voltage. I901 requires16V DC to operate normally. It will begin operation at6.8V DC on pin (4) of I901.When AC is applied, AC is routed through the main fuseF901 (a 6 Amp fuse), then through Line filters L901,and L902 to prevent any internal high frequency radia-tion back into the AC power line. After passing the fil-ters it arrives at the main full wave bridge rectifier D901where it is converted to 150V DC voltage to be suppliedto the power supply switching transformer T901 pin (1).One leg of the AC is routed to a half wave rectifier D906where it is rectified, routed through R903 and R904(22K ohm resistors), filtered by C910, clamped by a 30VZener D902 and made available to pin (4) of I901 asstart up voltage. When this voltage reaches 6.8Vdc, theinternal Regulator of I901 is turned On and begins theoperation of I901.When the power supply begins to operate by turning onand off the internal Switch MOS FET, the 150V DC routedthrough T901, in on pin 1 (Drain) and out on pin 2which is the Source. The Source of the internal SwitchMOS FET is routed out of pin (2) through three low ohmresistors to hot ground. When the internal Switch MOSFET turns on, it causes the transformer to saturate, build-ing up the magnet field. When the internal Switch MOSFET turns off, the magnet field collapses and the EMF iscoupled over to the secondary windings, as well as thedrive windings. The drive windings at pin (5) producea run voltage pulse which is rectified by D903, filteredby C909, then routed through R906, filtered again byC908, clamped by D902, and now becomes run voltage(16V) for I901.DEFLECTION POWER SUPPLY VISUAL LEDSThe Chassis has 4 Green and 1 Red LEDs on the Deflec-tion Power Supply PWB. This chassis utilizes 4 GreenLEDs in the power supply cold side and a Red LED in theHOT side.POWER ON MODEWhen the Power is turned ON, the LEDs light;1) DP06 Indicating Vcc applied to the Power SupplyDriver IC IP01 pin 4 (Colored RED)2) DP23 Indicating 115V Deflection B+ is available(Colored GREEN)3) DP37 Indicating SW +5V B+ is available (ColoredGREEN)4) DP11 Indicating SW +9V B+ is available (ColoredGREEN)5) DP35 Indicating 28V B+ is available (ColoredGREEN)LED USAGEThe Visual LEDs are useful in Trouble Shooting. Withoutremoving the back cover, some diagnostics can bemade. By observing the operation of the Red and GreenLEDs, the technician can determine if the DeflectionPower Supply is running. By monitoring these LEDs atturn on, one can determine if a line is loaded. If anLED tries to light then goes off, or only lights dimly, aloaded condition should be considered. Remember, thispower supply doesn’t operate when the set is inStandby. The following will examine each LED and howthey are lit.DP06Indicating Vcc applied to the Power Supply Driver ICIP01 pin 4 (Colored RED). If B+ (Vcc) is present onthe Deflection Power Supply Driver IC? LED will be ON.DP23Indicating 115V Deflection B+ is available (ColoredGREEN). This LED is connected directly to the 115 Vdeflection B+ line. If it’s lit, 115V is available.DP37Indicating SW +5V B+ is available (Colored GREEN).This LED is connected directly to the SW +5V B+ line.If it’s lit, +5V is available.DP11Indicating SW +9V B+ is available (Colored GREEN).This LED is connected directly to the SW +9V B+ line.If it’s lit, +9V is available.DP35Indicating 28V B+ is available (Colored GREEN). ThisLED is connected directly to the +28V B+ line. If it’slit, +28V is available.DEFLECTION POWER DRIVER B+ GENERATIONSTART UP VOLTAGE GENERATIONVcc for the Driver IC is first generated by the AC input.This voltage is called Start Up Voltage. IP01 requires21V DC to operate normally. It will begin to regulateat 14V DC on pin (4) of IP01.When AC is applied by the relay on the Sub PowerSupply R901, AC is routed through the connector PQD1.Then it arrives at the main full wave bridge rectifierDP01 where it is converted to DC voltage. One leg ofthe AC is routed through RP02 and RP03 (3.9K ohmresistors), filtered by CP05, and made available to pin(4) of IP01 as start up voltage. The Red LED DP03 isilluminated by this power supply. When this voltagereaches 6.8Vdc, the internal Regulator of IP01 is turnedOn.RUN VOLTAGE GENERATIONAfter the transformer TP91 is started, a pulse is outputfrom pin 8. This pulse is rectified by DP02, filtered by