A device for the restoration of kinescopes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Repair of kinescopes is an urgent and economically feasible task. To solve it, the author offers a simple device that you can make yourself. The device is much more compact and convenient to use, and most importantly - cheaper than branded ones, but not inferior to them in terms of efficiency.

Kinescope malfunctions are a fairly common problem when repairing TVs and monitors. High voltages and difficult temperature conditions soon reveal violations of technological standards when assembling a kinescope. Malfunctions of picture tubes are quite diverse and have their own ways of eliminating using various tricks. Most often, masters are faced with a decrease in cathode emission and interelectrode short circuit.

One of the methods for increasing the emission of cathodes is to increase the filament voltage of the kinescope. Another method is the regeneration of cathodes by a high-voltage discharge that burns out the surface layer. The success of this procedure, as the author sees it, depends largely not on the device itself and methods of influencing the surface of the active layer, but on the quality and condition of the cathodes of the restored kinescope. Interelectrode short circuits that occur due to the destruction of electron gun components are usually eliminated by passing a short-term pulsed current through the closed electrodes, for example, by discharging a capacitor. In essence, these processes are poorly controlled, and the results of recovery are unpredictable.

Various devices and methods for restoring the performance of kinescopes in general have long been developed and known. Currently, the circuitry of devices is being optimized through the use of modern element base, for example, microcontrollers are used to implement well-known algorithms. The ergonomics of instruments is being improved through the use of various indicators and scales. Working modes are modified. For example, to form a more stable electric discharge, pulse modulation of the voltage applied to the cathode is used. Modulation makes it possible to activate the process of electrical breakdown for a longer time at minimum regeneration currents and voltages. Periodic shutdown of the kinescope filament voltage during regeneration is used, which, due to a change in the temperature of the heater and cathode components, has an additional effect on the ongoing processes.

Basically, methods for restoring kinescopes were developed in the 50s ... 60s, now descriptions of instrument circuits and methods for restoring kinescopes are rare. Nevertheless, a device of this type is still necessary today for any master repairing TVs or monitors. Summarizing the experience of working with various devices, I offer my own version. It differs in that it provides for the possibility of pre-setting the current value in the zone of electrical breakdown. This solution, combined with ease of use, is a new solution in cathode regeneration.

The device is compact and easy to use, and in terms of efficiency it is not much different from complex branded devices in large elegant cases. It does not require a set of interchangeable panels for various types of kinescopes. The result of the restoration is observed immediately on the TV screen. Over the years of operation, the circuitry of the device has been well developed, the cost is low, even a radio amateur can assemble and configure it. Not a single TV or monitor has been harmed over many years of using the device, but, nevertheless, a warning: the author is not responsible for the consequences of using the proposed method and device.

A schematic diagram of the device is shown in Figure 1. The device consists of a power supply unit and a limiter-modulator. The power supply unit of the device includes components T1, D2, C1, C2. The rectifier on D2, through current-limiting resistors, charges the capacitors C1 and C2 to a voltage of 400 ... 450 V. The energy of the capacitor C2 is used to discharge in the kinescope through the limiter-modulator on Q1. The control voltage on the limiter-modulator is supplied from the capacitor C1. An independent power supply allows you to maintain the stability of the characteristics of the limiter when the capacitor C2 is discharged. To modulate the current source with reverse pulses, winding III of the transformer T1 is used. The depth of current modulation is set by resistor R4 within 40…60%. The current limit within 30 ... 800 mA is set by resistor R7. Red LED D3 is used as a base voltage stabilizer and indicator. Resistor R8 sets the value of the maximum current in the discharge circuit. Resistor R6 is limiting, R9 is a current sensor. Transistor Q1 can be used type BU508, S2000 or similar, but without a resistor in the base-emitter circuit. The average power dissipated by the transistor is small, so you can do without a heatsink. Diode D2 type BYW54 or any pulsed, with a reverse voltage of at least 600 V. Transformer T1 is wound on a ferrite core from a surge protector of a TV or monitor power supply, the dimensions of the core are not critical due to low power consumption. Winding I contains 20 turns of wire 0,53 mm, winding II - 180 ... 200 turns of wire 0,12 mm, winding III contains 30 turns of the same wire. Capacitors C1 and C2 are rated at 450 volts.

Rice. 1. Schematic diagram of the device

Structurally, the device is made in a compact plastic case. The positive terminal of the device and the wires for its connection to the glow terminals are equipped with alligator clips. It is convenient to draw a negative conclusion in the form of a probe, which is a thick metal needle mounted in a case from a felt-tip pen. It is convenient to place the SW1 button in the same probe.

Working with the device is as follows. We connect the power outputs with the help of "crocodiles" to the filament outputs of the kinescope of a working TV. The correct connection is determined by the glow of the LED D1. After a few seconds required to charge the capacitors, the device is ready for use. We connect the positive output to the modulator (most often it is a common wire), the negative one to the restored cathode. By setting the current to a minimum, we close the button SW1. The result of regeneration is checked by the quality of the image on the screen after the device is disconnected from the cathode. Figure 2 shows the output waveform. If necessary, increase the current with resistor R7, turn on the device and check the result again. Thus, by gradually increasing the current, it is possible to influence the cathodes of any kinescopes in the least "traumatic" way.

Rice. 2. Output waveform

In some TV models, protection may work during regeneration. In this case, the TV is restarted by turning it on again and the process can be continued. Long-term practice of using this device has shown that no defects appear in TV sets. If necessary, turning off the kinescope filament voltage can be simulated simply by turning off the TV. The temperature inertia of the cathodes and the energy stored in the capacitors of the device make it possible to carry out regeneration while maintaining the required modes. To supply a negative voltage, which is recommended in some methods, you just need to swap the leads connected to the kinescope. To use the device in lamp TVs or monitors that do not have a pulsed glow, it is necessary to wind a temporary additional winding of 3 ... 5 turns on a horizontal transformer and connect the power terminals of the device to it.

When working with the device, do not forget about the safety regulations.

Publication: library.espec.ws

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