A device for checking kinescopes in the Electronic magnifier mode. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Radio amateurs did not often use the “Electronic Magnifier” mode in their devices to check and restore the emission of picture tube cathodes. The author of the published article managed to make a simple device that implements just such a mode.

There are a lot of devices for testing picture tubes described in various technical literature. However, only the descriptions of three devices [1-3] are known (to the author), which provide testing in the “Electronic Magnifier” mode. But repeating them is not easy. Thus, in [1] the ratings of some parts and information about the line transformer are not indicated. Although the device described in [2] can not only test picture tubes in the “Electronic Magnifier” mode, but also restore the emission of their cathodes, it is therefore more complicated. In particular, to make it you need to wind four transformers, and it is especially difficult to make a high-voltage transformer. A similar device discussed in [3] contains fewer parts and is more compact. But it also requires winding three transformers, and also using three rather expensive transistors.

In connection with the above, a relatively simple device is proposed for repetition, which also operates in the “Electronic Magnifier” mode [1,2]. To make it, in addition to a ready-made old line transformer, you may have to wind only one more low-voltage transformer (if you don’t find a ready-made one) and use only one cheap transistor.

It should be recalled that in the “Electronic Magnifier” mode, a bright spot (projection of the cathode) of irregular circular shape appears in the central part of the kinescope screen. When focusing the image, areas of normal (light, uniformly colored areas) and decreased or increased (various darkening, flare, dots, etc.) emission of the cathode are visible on it. If the area of ​​dark areas of the image begins to increase during restoration of cathode emission, then the process must be stopped immediately, otherwise it will lead to destruction of the cathode emission layer.

The schematic diagram of the device is shown in fig. one.

The voltage converter in the device is based on a line transformer T1 from a tube TV - TVS110LA, a voltage multiplier E1 and a transistor KT818V. Moreover, it is necessary to use a transistor of the pn-p structure, since when using a transistor with a different structure, the pulse amplitude is smaller.

Power transformer T2 is selected based on the condition of obtaining two voltages 18...20 and 6,3 V at a current of 1 A. Voltage multiplier UN8,5/25-1,2A - from a color TV ULPTsTI or UPIMCT. Capacitor C3 - K73-13, C5 - MBGO. Resistor R4 - PP2-12 (wire). This resistor focuses the image on the kinescope screen. It can be taken from the mixing unit of ULPTSI TVs.

Cathode switch S1 - PG2-ZPZN. The KT818V transistor can be mounted on the aluminum frame of the TVS110LA transformer; only the panel into which the kenotron was inserted should be removed.

Contacts from a disassembled PL31b panel for the 61LK4Ts kinescope were used as connectors. The accelerating electrode of the kinescope being tested is connected to socket A1, the second anode to A2 (with a standard connector), the focusing electrode to F, the cathodes to R, G, B (respectively “red”, “green” and “blue”). The kinescope modulators are left free. The filament leads are connected to the filament winding III of transformer T2 through the same connectors.

On the front panel of the device, switch SA1, resistor R4 and a terminal block are attached for connecting the wires going to the kinescope being tested.

To check, connect the kinescope to the device through the appropriate connectors, and set the resistor R4 slider to maximum resistance (to the rightmost position in the diagram). Turn on the device. After the resistor R4 is warmed up by the engine, a projection of the switched-on cathode is displayed on the screen. Switch SA1 connect other cathodes and compare their projections. If there is insufficient vacuum in the kinescope, then an ionization glow will be noticeable in the bulb near the base.

In the device it is very easy to obtain a recovery mode for the emission of picture tube cathodes. To do this, it is necessary that the filament winding of transformer T2 provide, in addition to the nominal 6,3 V, additional voltages 8; 9,5 and 12,5 V. Another switch is added to switch them. Additionally, another resistor and a button are used, connected according to the diagram in Fig. 2.

The degree of charging of which depends on the position of the focus control R4 is connected to socket M. An additional switch is installed in the circuit of one of the terminals of winding II of transformer T2. It, the filament voltage switch and the SB1 button are also located on the front panel of the device.

When restoring cathode emission, you first need to warm up the kinescope at a nominal filament voltage (heater) of 6,3 V for 5... 10 minutes. In this case, turn off the converter with an additional switch. Then (at the first stage) a filament voltage of 8 V is sequentially applied to the heater for 2 minutes, 9,5 V for 2 minutes, 12,5 V for 1 s, 9,5 V for 30 s, 8 V for 30 s and finally 6,3 V. Turn on the converter again and check the cathodes of the kinescope.

If the result is unsatisfactory, proceed to the second stage of recovery. First, install the resistor R4 slider in the middle position for picture tubes with a screen diagonal of less than 51 cm, or in the extreme left (according to the diagram) position for picture tubes with a diagonal of 51 cm and larger. Then select the worst cathode with switch SA1, turn on the filament voltage of 8 V and press button SB1 four to five times at intervals of several seconds. The nominal filament voltage of 6,3 V is turned on again and the cathode being restored is checked.

Literature

1. Adamovich V. N. et al. The second life of color kinescopes. - M.: Radio and communication, 1992.
2. Makarets S. Restoration of kinescope cathodes. - Radio, 1996, No. 11, p. 10, 11.
3. Timoshkov A. A device for checking and restoring kinescopes. - Radio amateur, 2002, No. 2, S. 27, 28.

Author: S.Voronov, Moscow

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