Zenith B25A10Z Service Manuallines

Also see for B32A24Z: Operating guide Specifications

Contents

Zenith B25A10Z Service Manuallines Manual pdf 52 page image

CM151 3-1 CA - SERVICINGHIGH VOLTAGE AND X-RADIATION PROTECTIONA potential source of x-rays is the picture tube, if thehigh voltage (HV) is out of specification . When the HVis operating properly, there is no x-radiation . For theCA chassis family, the HV has no adjustments . A HVshutdown circuit is used to prevent excessive HV andx-ray emissions.THEORY OF OPERATION (SHUTDOWN CIRCUIT)This circuit basically monitors the sweep pulse voltagederived from the sweep transformer TX3204 pins 5 & 6.This voltage is rectified, and applied to a 12V zenerdiode ZDX3004. When the HV reaches its maximumallowed ,value (see drawing) the zener diode conducts,the voltage on pin 29 of the video processor (ICX2200)increases until it reaches the threshold voltage of 3.5VDC, and shuts down the TVIf the shutdown circuit has operated, themicrocontroller will prevent the TV from being turnedon again, without first having to unplug the AC cord toreset the microcontroller.SERVICINGSECTION 3TIP: Make a momentary short between the OUTPUT andGND of the IC6002 (RESET CIRCUIT) this will reset themicrocontroller IC6000.Apply signal through the video generator or tune theTV color receiver to crosshatch pattern. Connect anaccurate HV meter between the picture tube anode andchassis ground. Access Video Menu and adjustBrightness and Contrast controls for minimum screenluminance . Wait until, the Video Menu or displaydisappear. Read HV meter.SCREEN B+ VDC HV NOM HV MAXSIZE (0 BEAM) KV KV25 124.0 +/- 2% 28 2927 124.0 +/- 2% 27 2932 128.5 +/- 2% 30 31.536 128.5 +/- 2% 30 31.5MODULE LEVEL REPAIR ONLYCOMPONENT LEVEL REPAIRCA CHASSISSHUT DOWN CIRCUITVideo ProcessorICX2200RL2RINP29CGNDZDX3004DX3005RL1