A device for checking and restoring kinescopes. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A device for checking and restoring kinescopes. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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The device is designed to test and restore kinescopes, as well as other cathode ray tubes and radio tubes. It allows you to evaluate the emission current of the electron gun, check the presence of interelectrode short circuits and leaks in the circuits cathode - heater, cathode - modulator, accelerating electrode - modulator, accelerating electrode - focusing electrode, as well as between the electrodes of radio tubes: cathode - heater, cathode - control grid, screen grid - control grid, screen grid - pentode grid. If necessary, these combinations can be easily replaced by others.

Using the device, it is also possible to partially restore the emission of electron guns of kinescopes by calcining the cathode (training) or by discharging a capacitor. Moreover, emission can be restored at different filament voltages and at different discharge powers. You can also try to eliminate leaks and interelectrode short circuits in CRT and radio tube circuits.

A wide range of adjustment of incandescence and discharge power allows you to work with almost any electrovacuum devices. The scheme of the device is shown in Fig.1.

(click to enlarge)

Its main element is the network isolating transformer TV1, which allows you to change the filament voltage from 0 to 15 V in 0,5 V increments, as well as the voltage on the electrodes from 0 to 600 V.

Neon bulb HL2 and measuring head PA1 are used as indicators. The lamp indicates the presence of leaks, short circuits and breaks in the electrode circuits. Its glow becomes noticeable if the resistance of the series target in which it is included does not exceed 15 MΩ. In this case, a voltage of 300 ... 350 V must be applied to the circuit.

The measuring device is used as a calibrated indicator of the parameters of the tested CRT, as well as an indicator of the filament voltage. In a new tube, applying a voltage of 400 V to the modulator causes a cathode current of about 60 mA. During the aging phase, this current decreases to 10 mA and even to 1 mA.

Work with the device should begin with the connection of a CRT (radio tube) using an adapter cord with a panel for this type, after which the rated heating voltage is set using switches SA3, SA4. The control of the filament voltage is carried out by the PA1 measuring device in the first position of the SA6 switch.

Depending on the position of the SA4 switch, the filament voltage is changed by the SA3 switch from 0 to 7,5 V and from 7,5 V to 15 V, respectively. Switch SA5 turns on (off) the glow.

To check the purposes of the cathode - modulator (cathode - control grid), cathode - glow switch SA8 is switched to the "Cathode" position (in this case, the cathode is connected to the minus of the power source), and the switch SA6- to the position K-P or K-M, respectively.

Next, the SA2 switch is set to the "300 V" position, and the SA7 switch to the "HL" position. In this case, the glow of a neon bulb indicates the presence of a leak or short circuit in the cathode-heat or cathode-modulator circuit in accordance with the position of switch SA6. With a heated glow, the glow of a light bulb in the cathode-modulator circuit indicates the cathode current, and the brightness of the glow is directly proportional to the leakage current (emission current).

To eliminate a short circuit or leakage, briefly press the SB1 button. If the lamp continues to glow when the button is released, it is necessary to increase the discharge voltage with the SA2 switch and press the SB1 button again.

To control the circuits of the accelerating electrode - modulator (screen grid - control grid), and the accelerating electrode-focusing electrode (screen grid - pentode grid), switch SA8 is switched to the "Accelerate" position. In this case, an accelerating electrode (screen grid) is connected to the minus of the power source. Switch SA6 selects the electrode with respect to which the control will be carried out. To eliminate the noticed short circuits or leaks, you should also press the SB1 button (you must start with the lowest discharge voltage).

For color kinescopes, the cathode is selected by switch SA9.

After eliminating short circuits and leaks, you can begin to restore the emission current. Initially, it is necessary to control the current of the cathode (cathodes). To do this, switch SA6 is placed in the "K-M" position, switch SA8 is in the "Cathode" position, and switch SA7 is in the "RA" position. The voltage on the electrodes is selected by the SA2 switch within 400 V. Then, by pressing the SB1 button, the circuit is closed, and the device shows the cathode emission current.

At the first stage of recovery, the cathode should be calcined ("training"), then press the SB1 button and check the result. If the readings increased slightly, you can proceed to other recovery methods.

To do this, it is necessary to increase the voltage on the modulator with the SA2 switch to 500 ... .600 V. Then press the SB1 button and follow the readings of the device. While holding this mode, it is necessary to increase the current to 60 mA and then release the button. Heating of the cathode-heating unit does not lead to the formation of defects in it. The value of the current of the new tube in the specified mode can serve as a quality criterion. If this method does not give the desired result, it is necessary to turn the SA7 switch to the "HL" position. In this case, while pressing the button SB1, the discharge current of the capacitor C1 will flow through the cathode-modulator circuit.

In order not to damage the cathode, it is necessary to start recovery from the lowest discharge voltage (selected by switch SA2), and press the button for a short time (no more than 1 s). After each recovery, it is necessary to monitor the emission current and leakage.

If the desired result is not achieved, you can increase the filament voltage by 1 ... 2 V and repeat the recovery process again.

After the complete elimination of short circuits, leaks and the restoration of emission, it is necessary to "train" the cathode again.

The transformer can be wound on a Sh32 core, the width of the set is 50 mm. Winding W1-2-440 turns of PEV 0,2. Winding W3-10 - 1200 turns of PEV 0,12 with taps from 100,200,400,600,800 and 1000 turns. Winding W11-27 - 30 turns of PEV 0.51 with taps from the first 15 turns.

Authors: V.Yakovlev, Petrikov; Publication: N. Bolshakov, rf.atnn.ru

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