JPH04104591A - Degaussing circuit for cathode ray tube display device - Google Patents

Abstract

PURPOSE:To automatically perform degaussing by detecting the direction of the cathode ray display device and flowing direct current through a coil so as to be turned to the magnetic field at the time of initial adjustment. CONSTITUTION:The serial circuit of a manual degaussing switch 3, relay contact 6', and a relay driving circuit 4 with timer is parallely connected to the serial circuit of a degaussing coil 5 and a thermistor 11, further, a rotation detecting mechanism 10, a device direction detecting mechanism 9, a memory control circuit 7, a DC power supply 8, and a relay driving circuit 6 are equipped. When a power supply switch 2 and a manual degaussing switch 3 are turned on and the operations of the device direction rotation is performed, at first, the current flows through the degaussing coil 5, the degaussing operation is performed to degauss/uniform the magnetization of a shadow mask, then, the direction where this device is placed is detected, the difference in the direction of the optimum adjustment in a factory is detected in advance, the direct current flows the degaussing coil 5 so as to be turned to the magnetic field in the direction, and the constant direct current magnetic field is generated. Thus, the degaussing can be automatically performed even when the display device performs the change of the direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a degaussing circuit for demagnetizing magnetism in a shadow mask of a color cathode ray tube display device.

[Conventional technology]

Conventionally, this type of degaussing circuit has two types: one that conducts degaussing by passing a attenuation current through a thermistor to a degaussing coil installed around the shadow mask when the power switch is turned on, and the other that degauss the degaussing coil by pressing a manual degaussing switch whenever necessary. Some display devices perform demagnetization by passing an electric current through them, and display devices are equipped with one or both of the demagnetization circuits. In addition, due to problems such as color shift on the display screen, adjustments were made to the deflection yoke assembly of the cathode ray tube in consideration of the earth's magnetism.

[Problem to be solved by the invention]

In a display device equipped with the conventional degaussing circuit described above, if the direction of the display device (left or right) is changed during operation, the shadow mask of the cathode ray tube becomes magnetized due to the influence of the earth's magnetism, causing color shift on the display screen. A problem was occurring. Each time the orientation of the display device is changed in order to remove this magnetization, a manual demagnetization switch must be pressed to perform demagnetization. In addition, after changing the direction, the magnetic field is different from that at the time of initial adjustment (factory adjustment), so there are many problems such as color shift on the display screen, especially in large display devices. There were drawbacks such as the need to ensure that no trouble occurred during rotation, and a large amount of man-hours required for adjustment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a degaussing circuit that eliminates the drawbacks of the prior art and that automatically degausses the display device even when the display device changes orientation and maintains the optimum magnetic field when adjusting the cathode ray tube.

[Means to solve the problem]

The present invention provides a degaussing circuit for a shadow mask that includes a degaussing coil near the shadow mask of a cathode ray tube display device and degausses the coil by passing a damping current through the coil.
A mechanism that detects the rotation direction of the display device compares the rotation detection signal and direction detection signal from this detection mechanism with preset data, and sets the control circuit, DC power supply, and relay drive circuit to operate the display device. It is characterized by automatically demagnetizing the shadow mask each time it rotates, detecting the orientation of the device at that time, and generating a constant magnetic field by passing a direct current through the coil to match the magnetic field at the time of initial adjustment.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 shows a degaussing circuit according to an embodiment of the present invention. In this degaussing circuit, an AC power supply 1 or a power switch 2 common to the display device is used. It is connected to the degaussing coil 5 via a positive thermistor 11 and a relay contact 4'. The degaussing coil 5 is provided around the outside of the cathode ray tube near the shadow mask. Degaussing coil 5 and thermistor 11
Manual degaussing switch 3 and relay contact 6 are connected in parallel to the series circuit of
' and a series circuit of a relay drive circuit 4 with a timer are connected. Furthermore, rotation detection mechanism 10. Device direction detection mechanism 9. Memory control circuit 7. DC power supply 8. It has a relay drive circuit 6.

First, an outline of the operation of the circuit of this embodiment will be explained. Power switch on, manual degaussing switch on.

When various operations for rotating the device direction are performed, a current is applied to the degaussing coil and the demagnetizing operation is used to demagnetize the shadow mask and make it uniform.Then, the direction in which the device is placed is detected, and the direction in which the device is placed is detected. The difference from the optimal adjustment direction is detected, and a constant DC magnetic field is generated by passing a DC current through the degaussing coil so that the magnetic field is in that direction.

Next, the operation of this degaussing circuit will be explained in detail. When the power switch 2 is turned on, the circuit current flows through the manual degaussing switch 3, the relay contact 6', and the timer-equipped relay drive circuit 4. The timer-equipped relay drive circuit 4 is a circuit that is turned on for a set time to perform demagnetization and then turned off.

After the power switch 2 is turned on, the timer drives the relay for a certain set time, and the relay contact 4' turns on, and the current flows from the positive thermistor 11 to the relay contact 4' to the degaussing coil 5.
The current causes the resistance value of the positive thermistor 11 to rapidly increase, changing from several ohms to hundreds of ohms. For this reason, the circuit current generates a large magnetic field at the beginning, as shown in Figure 3.
It becomes an alternating magnetic field that gradually attenuates and demagnetizes the shadow mask of the cathode ray tube. After the set time, the timer-equipped relay drive circuit 4 is turned off, the relay contact 4' is turned off, no current flows through the degaussing coil, and the degaussing operation ends.

Next, the device direction detection mechanism 9 detects the current direction of the device, compares it with the direction in which the cathode ray tube assembly was optimally adjusted (factory adjustment), and operates the memory control circuit 7 so that the magnetic field is the same as the factory adjustment. A signal is sent to the DC power supply 8, and a current corresponding to this amount of change is passed through the degaussing coil 5 to generate a correction magnetic field, which is used as the magnetic field at the time of factory adjustment.

Next, when the manual degaussing switch 3 is pressed while the device is in operation, the current to the timer-equipped relay drive circuit 4 is temporarily turned off and the device returns to its initial state. Next, the timer-equipped relay drive circuit 4 is turned on, and current flows through the degaussing coil 5 through the positive polarity thermistor 711 to perform an operation similar to the automatic degaussing operation described above to perform demagnetization and magnetic field correction.

Next, when the display device rotates, the rotation detection mechanism 10 detects the rotation, and the device direction detection mechanism 9 detects the direction of the device at this time. As shown in FIG. 2, the rotation detection mechanism 10 and the device direction detection mechanism 9 are composed of a position display plate 13 attached to a part of the rotating part of the device and a position detector 12 attached to the fixed part of the device. There is. The position display board 13 has a detector 14 in which the device is attached (horizontal direction) and a magnet (Al to A8) on the outer circumference of the position display board 13.
) is attached, and the position detector 12 is an electromagnetic relay operated by magnetism. When the relay drive circuit 6 receives a signal from the circuit detection mechanism 10, it amplifies the signal, drives the relay for 1 to 2 seconds, and then returns to its original state. After that, the system refuses to accept signals for several tens of seconds.

Now, when the orientation of the display device is changed while it is in operation, the position detector 1 of the rotation detection mechanism 10
2 outputs a signal, and the rotation detection relay drive circuit 6 drives the relay according to the signal, keeping the relay contact 6' in an OFF state for 1 to 2 seconds. When the relay contact 6' is turned off, the timer-equipped relay drive circuit 4 enters the initial state and performs the same operation as when demagnetization is performed by pressing the manual degaussing switch. That is, a current flows through the positive-polarity thermistor 11 to the demagnetizing coil 5 to perform demagnetization, and a DC current flows to the demagnetizing coil 5 to correct the magnetic field.

〔Effect of the invention〕

As explained above, the present invention can prevent shadow mask magnetization due to the influence of earth's magnetism from occurring when the orientation of the display device is changed while the display device is in operation. The operation of the control circuit automatically demagnetizes the magnetic field, creating the optimum magnetic field adjusted at the factory.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a degaussing circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific example of a rotation detection mechanism for detecting left and right rotation of a display device, and a device direction detection mechanism, and FIG. 3 is a diagram of a circuit. FIG. 3 is a diagram showing a decaying current or a decaying alternating magnetic field. 1... AC power supply, 2... Power switch, 3... Manual degaussing switch, 4... Relay drive circuit with timer,
4', 6'... Relay contact, 5... Demagnetizing coil, 6
... Relay drive circuit, 7... Memory coil circuit,
8... DC power supply, 9... Device direction detection mechanism, 10.
... Rotation detection mechanism, 11... Thermistor, 12...
Position detector, 13... Position display board, 14... Direction detector.

Claims (1)

[Claims] A degaussing circuit is provided with a degaussing coil near the shadow mask of a cathode ray tube display device, and demagnetizes the coil by passing a damping current through the coil.The degaussing circuit includes a mechanism for detecting the circuit direction of the display device, and a rotation operated by a signal from this detecting mechanism. Degaussing of a cathode ray tube display device, characterized in that it is equipped with a detection circuit, a memory control circuit, a relay drive circuit, and a DC power supply circuit, automatically demagnetizes the display device every time it rotates, and generates a constant magnetic field with this coil. circuit.