Genius Essential Insights on Monitor Block Diagram for Models

U

The Switching Regulator is synchronized to the horizontal pulse and drives a power MOSFET. Unlike most regulators that have a common GND, this power supply has a common V+ and current is supplied from V- to GND. The MOSFET is connected to V– and signal ground (GND) through a transformer which is used as an inductor for series switch mode regulation. An operational amplifier, voltage reference, comparator, and oscillator in the power supply controller IC are used to accomplished regulation by means of pulse width modulation.

The transformer has two taps on the main winding which are used to generate the +16 volt and +24 volt supplies. It also has a secondary which is referenced to V- and supplies the power supply. Since the power supply is generating its own power, a special start up circuit is built into the power supply controller IC that delays start up until the capacitor which supplies the IC is charged up enough to furnish the current to start the power supply. This capacitor is charged with current through a high value resistor from the raw dc supply. This self sustaining action is why the power supply chirps when an overload or underload occurs. Additional secondaries to drive the horizontal raster shift circuit and the video amplifiers are also included in the power transformer.

V

The Load consists primarily of the horizontal flyback circuit. The power supply will not operate without the load since the voltage that sustains the power supply comes from a secondary in the power transformer and depends on some primary current to generate secondary current.

W

A+12V regulator is used to supply current, to all the control circuits in the monitor, with the exception of the power supply. Many of the control circuits are decoupled from the +12 volt line with a resistor or diode to minimize noise from common current loops.

X

The Over Voltage Protect circuit is built into the power supply and monitors the flyback transformer peak pulse voltage. This circuit will turn off the power supply and hold it off if the EHT exceeds its maximum rated value. Since excessive X-ray output occurs with excessive EHT, this circuit provides X-ray protection.

Y

The Fault Detector senses beam current and temperature. This circuit will activate the power supply shutdown circuit if either the maximum temperature is sensed or if the beam current becomes large enough to threaten the FBT.

Z

The Degaussing circuit is connected across the isolated AC line. A posistor is used to allow a large current to flow, in the degaussing coil, on power up. This current is then gradually reduced by the increased temperature of the positive temperature coefficient thermistor in the posistor. A relay is used to short the degaussing coil after the degaussing operation. This greatly reduces posistor residual current in the degaussing coil. When repairing a monitor, the degaussing coil should be unplugged, to avoid possible damage to the degaussing coil shorting relay.

14

		XX93 Monitor Block Diagram.
				On Video Board.					G2≈ 290V	2 For Dual Focus
GAME									G1≈ –20V
				VIDEO			Beam
VIDEO	3	VIDEO	3		3				3
				AMPS.			Current
		Interface							CRT
RGB				Bias			Feedback
		A			B
								C
				3					VDY	H
SYNC		BLANKING			Auto
				3
V. & H.		F.B.P.			Bright				HDY	≈	25KV
							G	3		EHT
		V retrace		3
		Beam limit						D
		M. gain
				CRT AUTO		Beam current
		High temp. limit
		I		BIAS IC			buffer

H. sync (FBP)

Program pulse

Dynamic Focus

SYNC

VERTICAL

V. sync

Grid pulse

used only on Dual

Interface

SYNC

CA3224E

Focus CRTs

E

J

DELAY

2

F

Horizontal

Dynamic

VERTICAL

Focus

Vs

VERTICAL

CONTROL &

H2

OSCILLATOR

OUTPUT

LA7851

LA7838

K

I. V. Feedback

L

V+

Vertical

+

Dynamic

G2

EHT

Focus

	LA7851			H1
	HORIZONTAL	H.	H.	FBT
Hs	CONTROL	Driver	Output	2
	Sync delay	N	O	P
	M
H. Pos.
		PINCUSHION
	V. Size &
	V. Ras. Pos.

REMOTE

HORIZONTAL

DIODE

CONTROLS

Size Control

Modulator

(PCB)

Q

R

S

Beam Current

+52V to +129V

ISOLATION

VOLTAGE

LOAD (VIDEO & DEFLECTION)

Transformer

DOUBLER

V

(IN GAME)

Raw DC

320V

+16V

+12V

+12V

T

SWITCHING

Regulator

V-

-200V

REGULATOR

+24-27V

W

Shutdown Sync

U

Vertical Deflection

Supply

DEGAUSSING

FAULT

OVER

+24V

VOLTAGE

FBP

CIRCUIT

DETECTOR

PROTECT

Z

Y

X

15