Zenith B32A24Z Service Manual download pdf (Page 53)

CM151 3-1 CA - SERVICING

HIGH VOLTAGE AND X-RADIATION PROTECTION

A potential source of x-rays is the picture tube, if the

high voltage (HV) is out of specification . When the HV

is operating properly, there is no x-radiation . For the

CA chassis family, the HV has no adjustments . A HV

shutdown circuit is used to prevent excessive HV and

x-ray emissions.

THEORY OF OPERATION (SHUTDOWN CIRCUIT)

This circuit basically monitors the sweep pulse voltage

derived from the sweep transformer TX3204 pins 5 & 6.

This voltage is rectified, and applied to a 12V zener

diode ZDX3004. When the HV reaches its maximum

allowed ,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 3.5

VDC, and shuts down the TV

If the shutdown circuit has operated, the

microcontroller will prevent the TV from being turned

on again, without first having to unplug the AC cord to

reset the microcontroller.

SERVICING

SECTION 3

TIP: Make a momentary short between the OUTPUT and

GND of the IC6002 (RESET CIRCUIT) this will reset the

microcontroller IC6000.

Apply signal through the video generator or tune the

TV color receiver to crosshatch pattern. Connect an

accurate HV meter between the picture tube anode and

chassis ground. Access Video Menu and adjust

Brightness and Contrast controls for minimum screen

luminance . Wait until, the Video Menu or display

disappear. Read HV meter.

SCREEN B+ VDC HV NOM HV MAX

SIZE

(

0 BEAM

)

KV KV

25 124.0 +/- 2% 28 29

27 124.0 +/- 2% 27 29

32 128.5 +/- 2% 30 31.5

36 128.5 +/- 2% 30 31.5

MODULE LEVEL REPAIR ONLY

COMPONENT LEVEL REPAIR

CA CHASSIS

SHUT DOWN CIRCUIT

Video Processor

ICX2200

RL2

RIN

P29

GND

ZDX3004

DX3005

RL1

1 2 ... 48 49 50 51 52 53 54 55 56 57 58 ... 110 111

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Zenith B32A24Z Service Manual Page 53

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