Shooting a kinescope with a suction cup. Picture tubes and their problems

We present a push-pull pulse converter assembled on a TL494 PWM controller. This makes the circuit quite simple and easy to repeat for many radio amateurs. At the output there are highly efficient rectifier diodes that double the voltage. You can also use a voltage converter without diodes - getting an alternating voltage. For example, for electronic ballasts (when powered by LDS), constant voltage and switching polarity are not relevant, since the ballast circuit has a diode bridge at the input. The schematic diagram is shown in the figure - click to enlarge.

The 12-220 V converter uses a ready-made high-frequency step-down transformer from the computer's AT or ATX power supply, but in our converter it will become a step-up transformer. Typically, these transformers differ only in size, and the location of the pins is identical. A non-working PC power supply can be found at any computer repair shop.

Operation of the circuit. Resistor R1 sets the width of the output pulses, R2 (together with C1) sets the operating frequency. We reduce the resistance R1 - we increase the frequency. We increase the capacitance C1 - we reduce the frequency. We use powerful MOS field transistors in the voltage converter, which are characterized by shorter response times and simpler control circuits. IRFZ44N, IRFZ46N, IRFZ48N work equally well here.

A radiator is not needed, since prolonged operation does not cause noticeable heating of the transistors. And if you still want to put them on a radiator, do not short-circuit the flanges of the transistor housings through the radiator! Use insulating gaskets and bushing washers from a computer power supply. However, for the first start, a radiator will not hurt; at least the transistors will not immediately burn out in the event of installation errors or a short circuit at the output.

A correctly assembled converter circuit does not require adjustment. It is advisable to use a non-metallic housing to prevent high voltage breakdown on the housing. Be careful when working with the circuit, as 220 V voltage is dangerous!

Discuss the article CONVERTER 12-220

Such an inverter is designed to produce alternating current 220 V 50 Hz from a car battery or any 12 V battery. The inverter power is about 150 W and can be increased to 300.

The circuit operates as a Push-Pull type converter. The heart of the inverter is the CD4047 microcircuit, which acts as a master oscillator and simultaneously controls field-effect transistors. The latter operate in key mode. Only one of the transistors can be open. If both transistors open at the same time, a short circuit will occur and the transistors will burn out instantly. This can happen due to improper management.

The CD4047 chip, of course, is not designed for high-precision control of field workers, but it copes with this task quite well.

The transformer was taken from a non-working UPS. It is 250-300 W and has a primary winding with a middle point where the plus from the power source is connected.

There are many secondary windings, so you need to find a 220 V network winding. Using a multimeter, the resistance of all taps that are on the secondary circuit is measured. The required leads should have the highest resistance (in the example, about 17 Ohms). All other wires can be bitten off.

It is recommended to check all components before soldering. It is better to select transistors from the same batch with similar characteristics. The capacitor in the frequency-setting circuit must have low leakage and a narrow tolerance. These parameters can be checked with a transistor tester.

A few words about possible replacements in the scheme. Unfortunately, the CD4047 chip has no Soviet analogues, so you need to buy it. “Field switches” can be replaced with any n-channel transistors that have a voltage of 60 V and a current of 35 A. Suitable from the IRFZ line.

The circuit also works great with bipolar transistors at the output, although the power will be much lower than when using field-effect transistors.

Gate limiting resistors can have a resistance of 10 to 100 ohms. It is better to set from 22 to 47 Ohms with a power of 250 mW.

The frequency-setting circuit must be assembled only from those elements indicated in the diagram. It will be finely tuned to 50 Hz.

A correctly assembled device should work immediately. But the first launch must be done with insurance. That is, in place of the fuse according to the diagram, install a resistor with a nominal value of 5-10 Ohms, or a 12 V (5 W) lamp, so as not to blow up the transistors if problems arise.

If the converter is working normally, the transformer makes a sound, and the keys should not heat up at all. If this is the case, then the resistor can be removed and power supplied directly through the fuse.

The average current consumption of an inverter at idle can be between 150 and 300 mA, but this will depend on the power supply and the transformer used.

Next, the output voltage is measured. In the example, the values ​​were from 210 to 260 V. This is within normal limits, since the inverter is not stabilized. Now you can turn on the load, for example, a 60 W lamp. You need to drive the inverter for about 10 seconds, the keys should heat up a little, since they do not yet have heat sinks. The heating on both keys should be uniform. If this is not the case, then look for jambs.

The inverter is equipped with a Remote Control function.

The main power plus is connected to the midpoint of the transformer. But for the inverter to work, it is necessary to apply a low-current plus to the board. This will start the pulse generator.

A few words about installation. As always, everything fits well in the computer's power supply case. Transistors are installed on separate radiators.

If a common heat sink is used, it is necessary to isolate the transistor housings from the radiator. The cooler was connected directly to the 12 V bus.

The biggest drawback of this inverter is the lack of short circuit protection. In this case, the transistors will burn out. To prevent this from happening, a 1 A fuse is needed at the output.

A low-power button supplies plus from the power source to the board, that is, it starts the inverter as a whole.

The power busbars from the transformer are attached directly to the radiators of the transistors.

By connecting a device called an energy meter to the output of the converter, you can make sure that the voltage and frequency are within normal limits. If the frequency differs from 50 Hz, then it must be adjusted using a multi-turn variable resistor, which is present on the board.

During operation, when no load is connected to the output, the transformer is quite noisy. When the load is connected, the noise is negligible. This is all normal, since rectangular pulses are supplied to the transformer.

The resulting inverter is unstabilized, but almost all household appliances are designed to operate in the voltage range from 90 to 280 V.

If the output voltage is higher than 300 V, then it is recommended to connect a 25-watt incandescent light bulb to the output in addition to the main load. This will reduce the output voltage to a small extent.

In principle, it is possible to power commutator motors from a converter, but they heat up 2 times more than when powered from a pure sine wave.

The same thing happens with consumers that have an iron transformer. But it is not recommended to connect asynchronous motors.

The weight of the device is about 2.7 kg. This is a lot when compared with pulse inverters.

Attached files:

How to make a simple Power Bank with your own hands: diagram of a homemade power bank

Colored spots are considered to be the main defects of picture tubes that appear during operation; they are a consequence of a violation of beam convergence; loss of color purity may also occur; reducing the emission of one or all three beams of an electronic spotlight.

The first two defects can be easily eliminated by demagnetizing the picture tube with a special demagnetization loop or a simple demagnetization choke. After this, if necessary, the standard procedure for bringing together the kinescope beams is performed. The same method is applicable to eliminate similar defects in domestic and imported picture tubes with a diagonal of 14, 20, 21 and 25 inches. In order to avoid defects in the convergence of rays and color purity in the TV in the future, you should install the TV away from any metal objects (the use of a metal stand or a metal frame for mounting the TV to the wall is completely unacceptable).

When you apply “mains voltage” to the TV, 220 volts are supplied to a type of thermistor called, through which the kinescope demagnetization loop located on its bandage is powered, i.e. on the back of the kinescope. When the TV is demagnetized, the posistor reduces the power supply to the loop. And so on every time you turn on the TV to the AC network. And if your TV is constantly in standby mode, that is, you turn it on only from the remote control, then power is supplied to the posistor continuously and the demagnetization system does not work. This is why you need to unplug your TV at least once a week.

“A posistor is a type of thermistor that changes its resistance depending on the temperature. In a cold state, the resistance of the posistor is low (5 - 15 Ohms), in a heated state it is more than 10 kOhms. It is connected to the TV's power circuit in series with the kinescope demagnetization loop. When the TV is turned on, the resistance of the posistor is low and current flows through it to the demagnetization loop. After heating, it gives greater resistance, which prevents the passage of voltage to the loop.

Quite often, spots on the kinescope can appear when a posistor fails. If you turn off and on the CRT TV from the network several times, and the spots do not disappear, then this indicates a failure of the posistor, which needs to be replaced.

To restore the kinescope demagnetization loop, you should replace the faulty posistor; this is not at all difficult. You just need to remove the back cover of the TV, pull out the board on which it is located and find the plug for turning on the demagnetization loop. Usually, it is located next to this plug.

The failed radio component must be unsoldered and a new one or a known good one soldered in its place.

can regulate the energy, amplitude and duration of the recovery pulse. This allows it to be used to restore almost all types of picture tubes, including those with planar cathodes, which are very sensitive to the parameters of restoration pulses

It is much worse if there is a third defect - a significant decrease in emission currents has occurred in the kinescope. This defect manifests itself in the coloration of a black-and-white image, in “strings” at the transition points between bright and dark parts of the image, in focusing problems (the image becomes cloudy), in a decrease in brightness and contrast.

If measurements show that the kinescope emission current has dropped below 100 µA, then the most radical way to correct the defect is to replace the kinescope. However, this is also the most expensive repair method. Therefore, we will consider other ways to extend the life of an “old” kinescope.

Without making significant changes to the TV circuit, you can make the following adjustments: increase the voltage on the accelerating electrode; increase the voltage on the second anode of the kinescope; increase the kinescope filament voltage; increase all voltages supplying the kinescope.

To regulate the voltage on the accelerating electrode, the TV provides resistor R9 on or resistor R27 on MS-41 when used in the TV MC-46 (the “Screen” regulator on TDKS imported TVs). When working with color modules that do not have an ABB system, an increase in the accelerating voltage also leads to an increase in image brightness. However, as a rule, when it increases above 800 V, OX lines appear on the screen.

Increasing the voltage on the second anode of the kinescope. The rated voltage on the second anode of a kinescope with a diagonal of 51, 54, 61 cm is 25 kV. In accordance with the technical specifications for the kinescope, it can be increased to 27.5 kV. In this case, there is a significant increase in image brightness at the same emission current of the kinescope cathodes. A further increase in voltage at the second anode is not recommended due to the increase in X-ray radiation from the kinescope. To increase the voltage on the second anode of the kinescope, a jumper is provided in the MS-41 and MS-3 horizontal scan modules, by breaking which you can reduce the capacitance of the capacitor connected in parallel with the horizontal scan output transistor. This is jumper XA2 on MS-41, which turns off the capacitor SY, and jumper XA1 on MS-3, which turns off capacitor C5.

Capacitors C10 and C5 have a capacity of 1000 pF, and disconnecting them may not be sufficient to significantly increase the voltage on the second anode of the kinescope. In this case, you can also reduce the capacitance of the second capacitor connected in parallel with the horizontal output transistor: C9 - in MS-41 and C4 - in MS-3. However, it should be remembered that reducing this capacitance to a value less than 4700 pF is dangerous for the horizontal output transistor - it can break through due to the too large amplitude of voltage surges at its collector. It should also be taken into account that in this case the kinescope filament voltages, accelerating and focusing voltages increase. Therefore, after changing the value of the indicated capacitors, the indicated voltages should be returned to their original values.

In any case, before increasing the voltage on the second anode of the kinescope, measures should be taken to prevent high-voltage breakdowns in the TV. To do this, with the TV turned off from the socket, use a damp cloth to carefully wipe off all the dust and dirt that has accumulated on the high-voltage elements of the TV: on the kinescope, high-voltage suction cup, high-voltage connecting wire, on the TVS (TDKS), on the multiplier, on the line scan module board, on the board kinescope and “Focusing” resistor, etc.

To increase the kinescope filament, the MS-41 module provides an adjustment choke L4 - “kinescope filament voltage.” By rotating its core, you can set the desired filament voltage. In the MC-3 module, the filament voltage can be increased by decreasing the value of resistors R11 and R12. It should be noted that the kinescope filament voltage should be increased very carefully and only in case of extreme necessity - long-term operation of the kinescope with a filament voltage of more than 6.8 V leads to irreversible changes in the active layer of the cathode, its depletion and the impossibility of restoring the properties of the electronic spotlight. The key to the longevity of a kinescope is its operation with a filament voltage of 6.3 ±0.1 V.

To generally increase the voltage supplying the kinescope, you can increase the horizontal scan supply voltage to 135...138 V. This is safe for the rest of the TV modules and at the same time leads to a significant increase in the brightness of the kinescope. However, after such an increase in the supply voltage, you should adjust the focusing of the kinescope, check that the filament voltage of the kinescope does not exceed 6.8 V and, if necessary, if OX appears, reduce the accelerating voltage.

Let's consider ways to eliminate specific defects in picture tubes

In a kinescope, the emission of one ray, for example, green, is significantly reduced.

In this case, the image on the screen takes on a lilac-purple tint. Color modules with ABB (MTs-41, MTs-46) may generally refuse to work with such a kinescope - the screen will be filled with a green raster with OX lines. In such a TV you should install a color module with manual adjustment of the black level and the range of RGB signals, for example, MTs-31. Then adjust it so that the parts of the black-and-white image that have average brightness (or the middle stripes in the test signal) do not have color casting. In this case, you will have to come to terms with the greenish color of the dark parts of the image and the purple color of the bright parts. However, when viewing a color image, this drawback is not very noticeable.

The image on the screen is “cloudy” and unfocused.

As a rule, in this case there is a decrease in the maximum brightness of the screen. All this indicates a significant decrease in the emission of the electronic spotlight or an increase in gas pressure inside the kinescope bulb. To increase gas pressure, i.e. A partial loss of vacuum is indicated by a blue glow in the kinescope bulb, clearly visible in the back of the kinescope, as well as frequent discharges in the kinescope - it “shoots”. In this case, the kinescope cannot be restored and needs to be replaced.

If there is no loss of vacuum, then you can try to restore the performance of the kinescope:

First of all, you should replace the color module (MC) with a module that does not have an ABB system (ABC
increase the accelerating voltage of the kinescope to a value at which the beam reverse only appears (800...900 V)
Use MC resistors to set the maximum range of output signals
resistors for adjusting the black level of the MC to achieve a satisfactory white balance in a b&w image; if necessary, you should also use resistors for this that regulate the range of the output RGB signals.

If after this the image is still not very good, you need to do the following: increase the voltage of the second anode of the kinescope, reducing the value of the capacitor parallel to the horizontal scan output transistor to 4700 pF (for horizontal scan modules, MS-41 and MS-3); focus and, if necessary, slightly reduce the accelerating voltage; make sure that the kinescope filament voltage has increased by no more than 5% relative to the original value and does not exceed 6.8 V. Otherwise, reduce the filament voltage by screwing in core L4 in the MS-41 module or increasing the values ​​of resistors R11 and R12 to 5 ,6...6.2 Ohm in the MS-3 module (if the kinescope is of domestic production).

The main factor leading to the aging of the kinescope and the degradation of the properties of the cathode is a disruption of the normal course of physical and chemical processes in its cathode. Even if all operating conditions of the kinescope are met, over time the concentration of barium in the oxide layer of the cathode decreases. This occurs due to the poisoning of the cathode by residual gases in the kinescope bulb and the evaporation of barium under the influence of the high temperature to which the cathode is heated. Initially, this causes large areas with reduced emissivity to appear on the cathode of the kinescope. And this, in turn, leads to an increase in the load on areas with normal emissivity and their accelerated degradation. The degradation mechanism of imported picture tubes is the same, in which, however, it takes a little longer to develop. This process is accelerated by frequent repetitions of the heating-cooling cycle of the cathode (cracking and shedding of the active layer of the cathode occurs), as well as by taking a large current from the cathode that has not yet been heated to the nominal temperature. But this is exactly what happens in the first minute of operation of any kinescope.

Thus, the service life of a kinescope cannot be infinite. However, if certain measures are taken, it can be significantly extended. At the same time, if special measures are not taken, when using a domestically produced kinescope in a 3...5USTST TV, after 4...5 years, the cathode emission current may drop by 80% of the original value. There are two main ways to combat the aging of kinescope cathodes:

delay in current extraction from cathodes until they are completely warmed up
use of constant filament kinescope.

The technical specifications for picture tubes 51LK2Ts and 61LK5Ts indicate the readiness time of the cathodes (warm-up time) - 15 seconds. However, often the cathodes do not heat up so quickly due to errors in the technological process of manufacturing electronic spotlights. In any case, increasing the warm-up time by more than 15 s before the current is drawn from the cathodes will only benefit the kinescope.

To delay the current draw while the cathodes are warming up, either a simple time relay is used, which locks the video amplifiers of the TV color module for a fixed time, or a device that locks the video amplifiers until the required kinescope currents are reached. The second method, of course, is preferable, and it is the one that is implemented in almost all modernized color modules: MTs-5.06, MTs-555, MTs-556M, MTs-655, MTs-755, MTs-777, MTs-97, MTs-7.99. In these modules, the nominal operating mode of the video amplifiers is turned on only after the emission current of the kinescope cathodes exceeds 200 μA. Thus, the image may appear on the TV screen with a delay of 15...25 s after it is turned on.

Eliminating this glitch is very simple, turn off the TV with the button on the case, not on the remote control, or unplug the cord from the outlet) wait ten minutes and turn it on. The defect may disappear.

Fantastic you say, but in fact it’s not so, every TV has a kinescope demagnetization system that is triggered when the TV is turned on with a button on the case, but not on the remote control. When was the last time you turned off the TV without using the remote control?