An oscilloscope attachment from a TV is the simplest circuit. Oscilloscope attachment for TV. Putting it all together

Descriptions of oscillographic TV attachments have already been published on the pages of the magazine ("Radio", 1959, No. 1; 1965, No. 8, etc.). However, unlike them, the proposed set-top box does not require intervention in the TV circuit (it is connected to the TV antenna socket). Together with a sweep frequency generator, it can be used to set up IF amplifiers for radio receivers.

The set-top box (Fig. 1 and 2) can be considered as a miniature television transmitter. Despite the relative simplicity of the circuit in this transmitter, a complete television signal, which differs from the standard signal only in the absence of equalizing pulses.

Frame sync pulses are generated from an alternating sinusoidal voltage by a limiting amplifier (T1), a differentiating circuit R8C4 and a threshold amplifier (T1). Their duration is about 1.9 ms.

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The blocking generator on the transistor Гз generates horizontal sync pulses. These are not the main pulses of the blocking generator, but surges of the collector voltage that occur immediately after the main ones. A diode D3 is connected between the collectors of transistors T4 and T5. At the moment the main pulse is generated, the collector of transistor T4 is closed to the chassis through the open transistor T5 and diode D3. As a result, insets appear in the vertical sync pulses, which, as required, precede the horizontal sync pulses. The windings of the transformer Tr1 of the blocking generator are wound on a toroidal core made of oxyphere (H=1000). The outer diameter of the core is 10 mm, a. thickness 2 mm. Windings I and III contain 100 turns each, ll - 30 turns of PELSHO 0.1 wire.

At the beginning of the horizontal scan period, the voltage pulse of the blocking generator quickly charges capacitor C5 through diode D2. During the rest of the period it is slowly discharged through resistor R6. The resulting sawtooth voltage is supplied to the base of transistor T2. Here it is added to the oscilloscope voltage.

The three-stage amplifier (T2, T3, T6), due to its high gain (50000-100000), operates practically in relay mode, characterized by a certain response threshold. Since an oscillograph voltage is superimposed on the input sawtooth voltage of the amplifier, the switching of the output voltage coincides in time with the moment when the total voltage passes through the response threshold of the amplifier. The rise time of the front of the voltage pulses at the output of the amplifier is small, again due to the high gain. The moment of appearance of these pulses during the horizontal scan period is determined by the instantaneous value of the oscilloscope voltage. The attachment parameters are chosen such that in the absence of the voltage being tested, the center line is in the center of the screen. If necessary, the image on the screen can be shifted in one direction or another by changing the resistance of resistor R3.

To improve the clarity of the line image on the TV screen, the amplifier (T2, T3, T6) is covered by a positive feedback from the collector of transistor T3 to the base of transistor T2 through capacitor C6. This significantly increases the gain in the area high frequencies and, therefore, increases the slope of the front of the output pulses. Visually, this manifests itself in an increased sharpness of the transition from white to black.

Frame, line and video pulses are added at the input of the emitter follower (T7), which is the modulation amplifier of the VHF generator (T8). The latter is assembled according to a three-point capacitive circuit. The generation frequency must be chosen equal to the carrier frequency of the image of a free television channel. Otherwise, the set-top box may interfere with the operation of neighboring TVs. The required generation frequencies can be achieved by selecting the number of turns of coil L1. When tuning to the second television channel (59.25 MHz), coil L1 contains 5 turns of PEV 0.6 wire, coil diameter 9 mm.

The modulated RF voltage is supplied to the output of the set-top box through a divider R18-R19, which reduces the voltage to 3 mV to avoid overloading the RF path of the TV.

The output of the set-top box is connected with a coaxial cable or twisted double wire to the antenna input of the TV.

Construction and setup. All parts of the set-top box, with the exception of the VHF generator, can be placed on the circuit board in any order. Parts related to the VHF generator (C11-C15, L1, T8) must have short leads, be connected to each other by short conductors, and in addition, they should be grouped in one place.

No shielding of the console is required. After turning it on, you need to adjust the TV as usual using the adjustment knobs (frame rate, line frequency, contrast). If the frequency of the pulses of the blocking generator of the set-top box does not lie in the range of adjusting the line frequency of the TV, you need to enter it into this range by changing the resistance of resistor R14 within small limits. It should be noted that the synchronization of the TV scans from the set-top box is usually very stable, so poor synchronization when setting up the set-top box indicates some kind of installation error. To achieve precise tuning of the VHF generator of the set-top box to the selected television channel, you have to stretch or compress the turns of the winding of coil L1 (that is, change the winding pitch). At correct setting the line on the screen is sharply outlined.

The parameters of the set-top box are selected so that the largest range of images on the TV screen corresponds to an input voltage of about 0.3 V. The sensitivity of the set-top box can be adjusted by changing the resistance of resistor R2.

To check the sensitivity of the set-top box, an alternating voltage of a known magnitude is supplied to its input either from a power source with a voltage of 6 V, a frequency of 50 Hz through a divider, or from a sound generator.

If desired, the input impedance and sensitivity of the set-top box can be significantly increased by connecting to it regular amplifier LF with emitter follower at the input.

The attachment, the diagram of which is shown in Fig. 1, turns any TV into an oscilloscope with big screen. You can observe low-frequency oscillations on it, and with the help of a sweep frequency generator (SWG) you can visually tune the IF amplifiers of radio receivers.

The set-top box can be considered as a miniature television transmitter. Despite the relative simplicity of the circuit, this transmitter generates a complete television signal, which differs from the standard signal only in the absence of equalizing pulses.

Frame sync pulses are generated from alternating sinusoidal voltage by the limiting amplifier T1, the differentiating circuit R8C4 and the threshold amplifier T4. Their duration is about 1.9 ms.

At the moment of generation of the main pulse, the collector of transistor T4 is closed to the chassis through the open transistor T5 and diode D3. As a result, insets appear in the vertical sync pulses, which, as required, precede the horizontal sync pulses. The windings of the transformer Tr1 of the blocking generator are wound on a toroidal core made of oxyfer (ts = 1000).

The outer diameter of the core is 10 mm, thickness 2 mm. Windings I and III contain up to 100 turns, and Winding II - 30 turns of PELSHO 0.1 wire.

Here it is added to the oscilloscope voltage.

Rice. 1. An attachment that turns a TV into an oscilloscope: a - block diagram: A - block for generating frame synchronization pulses; B - line synchronization pulse generator; C - blocking generator; o-block, converting voltage into video pulses; E - VHF generator with amplitude modulation; “Input” - terminals to which the voltage being tested is supplied: b - circuit diagram.

The three-stage amplifier (T2, T3, T6), due to its large gain coefficient (50,000-100,000), operates practically in relay mode, characterized by a certain response threshold.

The attachment parameters are chosen such that in the absence of the voltage being tested, the center line is in the center of the screen. If necessary, the image on the screen can be shifted in one direction or another by changing the resistance of resistor R3.

To improve the clarity of the line image on the TV screen, the amplifier (T2, T3, T6) is covered by positive feedback from the collector of transistor T3 to the base of transistor T2 through capacitor C6. This significantly increases the gain in the high frequency region and, therefore, increases the slope of the front of the output pulses. Visually, this manifests itself in an increased sharpness of the transition from white to black.

Frame, line and video pulses are added at the input of the emitter follower T7, which is the modulation amplifier of the VHF generator T8. The latter is assembled according to a three-point capacitive circuit. The generation frequency must be chosen equal to the carrier frequency of the image of a free television channel.

Otherwise, the set-top box may interfere with the operation of neighboring TVs. The required generation frequencies can be achieved by selecting the number of turns of coil L1. When tuning to the second television channel (59.25 MHz), coil L1 contains 5 turns of PEV 0.6 wire, coil diameter 9 mm.

The modulated RF voltage is supplied to the output of the set-top box through a divider R18 - R19, which reduces the voltage to 3 mV to avoid overloading the RF path of the TV.

The output of the set-top box is connected with a coaxial cable or twisted double wire to the antenna input of the TV.

Construction and setup. All parts of the set-top box, with the exception of the VHF generator, can be placed on the circuit board in any order. The parts related to the VHF generator (C11 - C15, L1, T8) must have short leads, be connected to each other by short conductors, and, in addition, they should be grouped in one place.

No shielding of the console is required. After turning it on, you must, as usual, adjust the TV using the adjustment knobs (frame rate, line frequency, contrast).

If the pulse frequency of the blocking generator of the set-top box does not lie in the range of adjusting the line frequency of the TV, it is necessary to enter it into this range by changing the resistance of resistor R14 within small limits. It should be noted that the synchronization of the TV scans from the set-top box is usually very stable, so poor synchronization when setting up the set-top box indicates some kind of installation error.

To achieve precise tuning of the VHF generator of the set-top box to the selected television channel, you have to stretch or compress the turns of the winding of coil L1, i.e. change the winding pitch. When set correctly, the line on the screen is sharply defined.

The parameters of the set-top box are selected so that the largest range of the image on the TV screen corresponds to an input voltage of about 0.3 V. The sensitivity of the set-top box can be adjusted by changing the resistance of resistor R2.

If desired, the input impedance and sensitivity of the set-top box can be significantly increased by connecting to it a conventional low-frequency amplifier with an emitter follower at the input.

Literature: V.G. Bastanov. 300 practical advice, 1986

An oscilloscope is portable device, which was created for testing microcircuits. Additionally, many models are suitable for industrial inspection and can be used to carry out various measurements. You cannot make an oscilloscope with your own hands without a zener diode, which is its main element. This part is installed in devices of varying power.

Additionally, depending on the modification, devices may include capacitors, resistors and diodes. The main parameters of the model include the number of channels. Depending on this indicator, the maximum bandwidth changes. Also, when assembling an oscilloscope, you should consider the sampling rate and memory depth. In order to analyze the received data, the device is connected to a personal computer.

Circuit of a simple oscilloscope

Scheme simple oscilloscope includes a 5 V zener diode. Its throughput depends on the types of resistors that are installed on the chip. To increase the amplitude of oscillations, capacitors are used. You can make a probe for an oscilloscope with your own hands from any conductor. In this case, the port is selected separately in the store. Resistors of the first group must withstand a minimum resistance in the circuit of 2 ohms. In this case, the elements of the second group should be more powerful. It should also be noted that there are diodes on the circuit. In some cases they form bridges.

Single channel model

You can make a single-channel digital oscilloscope with your own hands only using a 5 V zener diode. Moreover, more powerful modifications are unacceptable in this case. This is due to the fact that an increased maximum voltage in the circuit leads to an increase in the sampling frequency. As a result, the resistors in the device fail. Capacitors for the system are selected only of the capacitive type.

The minimum resistance of the resistor should be 4 ohms. If we consider the elements of the second group, then the transmission parameter in this case should be 10 Hz. In order to increase it to the required level, they use various types regulators. Some experts recommend using orthogonal resistors for single-channel oscilloscopes.

In this case, it should be noted that they raise the sampling rate quite quickly. However, there are still negative aspects in such a situation, and they should be taken into account. First of all, it is important to note the sharp excitation of vibrations. As a result, signal asymmetry increases. Additionally, there are problems with the sensitivity of the device. Ultimately, the accuracy of the readings may not be the best.

Dual Channel Devices

Making a two-channel oscilloscope with your own hands (the diagram is shown below) is quite difficult. First of all, it should be noted that zener diodes in this case are suitable for both 5 V and 10 V. In this case, capacitors for the system must be used only of a closed type.

Due to this, the device’s bandwidth can increase to 9 Hz. Resistors for the model are usually used of the orthogonal type. In this case, they stabilize the signal transmission process. To perform addition functions, microcircuits are mainly selected from the MMK20 series. You can make a divider for an oscilloscope with your own hands from a regular modulator. It's not particularly difficult.

Multi-channel modifications

In order to assemble a USB oscilloscope with your own hands (the diagram is shown below), you will need a fairly powerful zener diode. The problem in this case is increasing the throughput of the circuit. In some situations, the operation of resistors may be disrupted due to a change in the limiting frequency. In order to solve this problem, many use auxiliary dividers. These devices greatly help to increase the threshold voltage limit.

You can make a divider using a modulator. Capacitors in the system must be installed only near the zener diode. To increase the bandwidth, analog resistors are used. The negative resistance parameter fluctuates on average around 3 ohms. The blocking range depends solely on the power of the zener diode. If the limiting frequency drops sharply when the device is turned on, the capacitors must be replaced with more powerful ones. In this case, some experts recommend installing diode bridges. However, it is important to understand that the sensitivity of the system in this situation deteriorates significantly.

Additionally, it is necessary to make a probe for the device. To ensure that the oscilloscope does not conflict with personal computer, it is more expedient to use a microcircuit of the MMP20 type. You can make a probe from any conductor. Ultimately, a person will only have to buy a port for him. Then, using a soldering iron, the above elements can be connected.

Assembling a 5 V device

At 5 V, a do-it-yourself oscilloscope attachment is made only using an MMP20 type microcircuit. It is suitable for both ordinary and powerful resistors. The maximum resistance in the circuit should be 7 ohms. In this case, the bandwidth depends on the signal transmission speed. Dividers for devices can be used in the most different types. Today, static analogues are considered more common. The bandwidth in this situation will be around 5 Hz. To increase it, it is necessary to use tetrodes.

They are selected in the store based on the limiting frequency parameter. To increase amplitude reverse voltage many experts advise installing only self-regulating resistors. In this case, the signal transmission speed will be quite high. At the end of the work, you need to make a probe to connect the circuit to a personal computer.

10V Oscilloscopes

A do-it-yourself oscilloscope is made with a zener diode, as well as closed-type resistors. If we consider the device parameters, the vertical sensitivity indicator should be at the level of 2 mV. Additionally, the bandwidth must be calculated. To do this, the capacitance of the capacitors is taken and correlated with the maximum resistance of the system. Resistors for the device are most suitable of the field type. To minimize the sampling frequency, many experts advise using only 2 V diodes. Due to this, high signal transmission speeds can be achieved. In order for the tracking function to be performed quite quickly, the microcircuits are installed like MMP20.

If you plan storage and playback modes, you must use a different type. Cursor measurements will not be available in this case. The main problem with these oscilloscopes can be considered a sharp drop in the limiting frequency. This is usually due to the rapid expansion of data. The problem can be solved only with the use of a high-quality divider. At the same time, many also rely on a zener diode. You can make a divider using a conventional modulator.

How to make a 15 V model?

You can assemble an oscilloscope yourself using linear resistors. They can withstand a maximum resistance of 5 mm. Due to this, there is not much pressure on the zener diode. Additionally, care should be taken when choosing capacitors for the device. For this purpose, it is necessary to measure the threshold voltage. Experts use a tester for this.

If you use tuning resistors for an oscilloscope, you may encounter increased vertical sensitivity. Thus, the data obtained due to testing may be incorrect. Considering all of the above, it is necessary to use only linear analogues. Additionally, care should be taken to install the port, which is connected to the microcircuit via a probe. In this case, it is more expedient to install the divider through the bus. To prevent the oscillation amplitude from being too large, many advise using vacuum-type diodes.

Using PPR1 series resistors

Making a USB oscilloscope with your own hands using these resistors is not an easy task. In this case, it is necessary first of all to evaluate the capacitance of the capacitors. To ensure that the maximum voltage does not exceed 3 V, it is important to use no more than two diodes. Additionally, you should remember the nominal frequency parameter. On average this figure is 3 Hz. Orthogonal resistors are not uniquely suitable for such an oscilloscope. Construction changes can only be made using a divider. At the end of the work, you need to directly install the port.

Models with PPR3 resistors

You can make a USB oscilloscope with your own hands using only grid capacitors. Their peculiarity is that the level of negative resistance in the circuit can reach 4 ohms. A wide variety of microcircuits are suitable for such oscilloscopes. If we take the standard version of the MMP20 type, then it is necessary to provide at least three capacitors in the system.

Additionally, it is important to pay attention to the density of the diodes. In some cases, this affects the bandwidth. To stabilize the division process, experts advise carefully checking the conductivity of the resistors before turning on the device. Lastly, the regulator is directly connected to the system.

Devices with vibration suppression

Oscilloscopes with an oscillation suppression unit are used quite rarely these days. They are most suitable for testing electrical appliances. Additionally, their high vertical sensitivity should be noted. In this case, the limit frequency parameter in the circuit should not exceed 4 Hz. Due to this, the zener diode does not overheat significantly during operation.

You can make an oscilloscope yourself using a grid-type microcircuit. In this case, it is necessary to decide on the types of diodes at the very beginning. Many people in this situation advise using only analog types. However, in this case, the signal transmission speed may be significantly reduced.

The attachment, the diagram of which is shown in Fig. 76, turns any TV into a large-screen oscilloscope. You can observe low-frequency oscillations on it, and with the help of a sweep frequency generator (SWG) you can visually tune the IF amplifiers of radio receivers.

Frame sync pulses are generated from an alternating sinusoidal voltage by a limiting amplifier 77, a differentiating circuit R8C4 and a threshold amplifier T4. Their duration is about 1.9 ms.

The blocking generator on transistor T5 generates horizontal sync pulses. These are not the main pulses of the blocking generator, but surges of the collector voltage that occur immediately after the main ones. A DZ isolation diode is connected between the collectors of transistors T4 and T5. At the moment of generation of the main pulse, the collector of transistor T4 is closed to the chassis through the open transistor T5 and the DZ diode. As a result, insets appear in the vertical sync pulses, which, as required, precede the horizontal sync pulses. The windings of the transformer Three blocking generator are wound on a toroidal core made of oxyfer (ts = 1000). The outer diameter of the core is 10 mm, thickness 2 mm. Windings I and III contain up to 100 turns, and Winding II - 30 turns of PELSHO 0.1 wire.

A three-stage amplifier (T2, T3, TB), due to its large gain coefficient (50,000-100,000), operates practically in a relay mode, characterized by a certain response threshold.

Rice. 76. An attachment that turns a TV into an oscilloscope:

a — block diagram: L—block for generating frame synchronization pulses; B — line synchronization pulse generator; C - blocking generator; D—block that converts voltage into video pulses; E - VHF generator with amplitude modulation; “Input” - terminals to which the voltage being tested is supplied: 6 - circuit diagram

To improve the clarity of the line image on the TV screen, the amplifier (T2, T3, Tb) is covered by positive feedback from the collector of transistor T3 to the base of transistor T2 through capacitor Sb. This significantly increases the gain in the high frequency region and, therefore, increases the slope of the front of the output pulses. Visually, this manifests itself in an increased sharpness of the transition from white to black.

Frame, line and video pulses are added at the input of the emitter follower 77, which is the modulation amplifier of the T8 VHF generator. The latter is assembled according to a three-point capacitive circuit. The generation frequency must be chosen equal to the carrier frequency of the image of a free television channel. Otherwise, the set-top box may interfere with the operation of neighboring TVs. The required generation frequencies can be achieved by selecting the number of turns of coil L1. When tuning to the second television channel (59.25 MHz), coil L1 contains 5 turns of PEV 0.6 wire, coil diameter 9 mm.

The modulated RF voltage is supplied to the output of the set-top box through a divider R18 - R19, which reduces the voltage to 3 mV to avoid overloading the RF path of the TV.

The output of the set-top box is connected with a coaxial cable or twisted double wire to the antenna input of the TV.

Construction and installation. All parts of the set-top box, with the exception of the VHF generator, can be placed on the circuit board in any order. The parts related to the VHF generator (C11 - C15, L1, T8) must have short leads, be connected to each other by short conductors, and, in addition, they should be grouped in one place.

No shielding of the console is required. After turning it on, you must, as usual, adjust the TV using the adjustment knobs (frame rate, line frequency, contrast). If the pulse frequency of the blocking generator of the set-top box does not lie in the range of adjusting the line frequency of the TV, it is necessary to enter it into this range by changing the resistance of resistor R14 within small limits. It should be noted that the synchronization of the TV scans from the set-top box is usually very stable, so poor synchronization when setting up the set-top box indicates some kind of installation error. To achieve precise tuning of the VHF generator of the set-top box to the selected television channel, you have to stretch or compress the turns of the winding of coil L1, i.e. change the winding pitch. When set correctly, the line on the screen is sharply defined.

If desired, the input impedance and sensitivity of the set-top box can be significantly increased by connecting to it a conventional low-frequency amplifier with an emitter follower at the input.

To check and configure transistor receivers, portable tape recorders, computers and other devices, it is necessary to measure voltages from hundredths of a volt. For such measurements, a lamp or transistor volt-ohmmeter is required. direct current. On the…….

Measuring bridge, the diagram of which is shown in Fig. 89, allows you to measure the resistance of resistors in the range from 10 Ohms to 10 MOhms and capacitor capacities from 10 pF to 10 μF. Generator…….

Digital multimeter (tester), the circuit diagram of which is shown in Fig. 86, is structurally made on the integrated circuit K572PV2A (B, V) (BIS). Main technical parameters of the tester Range of measured values: Constant voltage 1–19.99…….

Universal measuring instruments- ampere-volt meters (avometers) - allow you to measure, with a relatively simple circuit, all the electrical quantities necessary in the practice of a radio amateur: voltage, current, resistance. In Fig. 31.1, 31.2 and 31.5 are shown…….

A universal testing device, the circuit diagram of which is shown in Fig. 84, can work as a voltmeter, ohmmeter, signal generator, transistor, diode, electrolytic capacitor, quartz resonator tester. Voltmeter. To measure DC voltage…….

Oscilloscope - from an old TV

TV as an oscilloscope

The attachment, the diagram of which is shown in Fig. 1, turns any TV into a large-screen oscilloscope. You can observe low-frequency oscillations on it, and with the help of a sweep frequency generator (SWG) you can visually tune the IF amplifiers of radio receivers.

Rice. 1. An attachment that turns a TV into an oscilloscope:
a - block diagram:
A - block for generating frame synchronization pulses;
B - pulse generator line synchronization;
C - blocking generator;
D - block that converts voltage into video pulses;
E - VHF generator with amplitude modulation;
“Input” - terminals to which the voltage being tested is supplied:
b - electrical circuit diagram.

Frame sync pulses are generated from an alternating sinusoidal voltage by the limiting amplifier T1, the differentiating circuit R8C4 and the threshold amplifier T4. Their duration is about 1.9 ms.

The blocking generator on transistor T5 generates horizontal sync pulses. These are not the main pulses of the blocking generator, but surges of the collector voltage that occur immediately after the main ones. A diode D3 is connected between the collectors of transistors T4 and T5. At the moment of generation of the main pulse, the collector of transistor T4 is closed to the chassis through the open transistor T5 and diode D3. As a result, insets appear in the vertical sync pulses, which, as required, precede the horizontal sync pulses. The windings of the blocking generator transformer Tp1 are wound on a toroidal core made of oxyfer (= 1000). The outer diameter of the core is 10 mm, thickness 2 mm. Windings I and III contain up to 100 turns, and Winding II - 30 turns of PELSHO 0.1 wire.

The three-stage amplifier (T2, T3, T6), due to its high gain (50,000 - 100,000), operates practically in relay mode, characterized by a certain response threshold.

To improve the clarity of the line image on the TV screen, the amplifier (T2, T3, T6) is covered by positive feedback from the collector of transistor T3 to the base of transistor T2 through capacitor C6. This significantly increases the gain in the high frequency region and therefore increases the slope of the output pulses. Visually, this manifests itself in an increased sharpness of the transition from white to black.

Frame, line and video pulses are added at the input of the T7 emitter follower, which is the modulation amplifier of the T8 VHF generator. The latter is assembled according to a three-point capacitive circuit. The generation frequency must be chosen equal to the carrier frequency of the image of a free television channel. Otherwise, the set-top box may interfere with the operation of neighboring TVs. The required generation frequencies can be achieved by selecting the number of turns of coil L1. When tuning to the second television channel (59.25 MHz), coil L2 contains 5 turns of PEV 0.6 wire, coil diameter 9 mm.

The modulated RF voltage is supplied to the output of the set-top box through a divider R18 - R19, which reduces the voltage to 3 mV to avoid overloading the RF path of the TV.

The output of the set-top box is connected with a coaxial cable or twisted double wire to the antenna input of the TV.

Construction and setup. All parts of the set-top box, with the exception of the VHF generator, can be placed on the circuit board in any order. The parts related to the VHF generator (C11 - C15, L1, T8) must have short leads, be connected to each other by short conductors, and, in addition, they should be grouped in one place.

If desired, the input impedance and sensitivity of the set-top box can be significantly increased by connecting to it a conventional low-frequency amplifier with an emitter follower at the input.

The TV turns into an oscilloscope by turning the switch knob

Turn the switch knob and the TV turns into an oscilloscope. It can be used in physics lessons at school, in the laboratory and in amateur radio practice. The secret of turning a TV into an oscilloscope is in a small attachment, which is mounted on the back wall of the TV and is a switch that is used to switch the power circuit of the deflection system (Fig. 2).

Rice. 2. Electrical diagram of the console-switch.

In switch position 1, the TV operates as usual. In position 2 P1, the voltage from the horizontal scan generator is turned off. If you now connect a signal to terminals Y, an oscillogram of the process under study will appear on the TV screen. Synchronization is set by rotating the “Frame Rate” knob. Using the “Vertical Size” control, the oscillogram can be compressed or stretched along the X axis. In position 3 of the switch, the deflection system is completely disconnected from the power supply. Then, by applying voltage to terminals X and Y, Lissajous figures are observed.

So, using the set-top box, you can demonstrate and observe a wide variety of processes: rectification of alternating current, addition of mutually perpendicular oscillations, phase shift with inductive and capacitive loads, damped oscillations, beating, etc. The device is designed for TVs “Record”, “Volkhov” , “Yenisei”, but it is not difficult to configure it to work with any other television receiver.

An oscilloscope is a whole measuring laboratory for input control

During the manufacture and repair of radio-electronic equipment, various radio elements are installed. To ensure their serviceability, a preliminary (input) test is carried out, which can be carried out using an attachment to any oscilloscope. Schematic diagram attachments are shown in Fig. 3.

Rice. 3. Schematic diagram of the oscilloscope attachment.

The oscilloscope attachment allows you to check almost all elements installed in electronic devices of household equipment: from resistors to controlled valves (thyristors), and also makes it possible to evaluate the quality of potentiometers, inductors, serviceability of switches, relays, transformers, etc.

Thus, one oscilloscope can replace almost the entire incoming inspection laboratory.

It must be borne in mind that the oscilloscope is used not only for observing various processes associated with changes in the voltage shape. The oscilloscope can be used as an electronic voltmeter, ohmmeter, and by using the attachment to the oscilloscope, you can observe the characteristics of transistors on the oscilloscope screen, which expands the possibilities of using the oscilloscope in repair and amateur practice.

The set-top box is assembled in a metal or plastic case with dimensions of 50x75x100 mm using a small-sized transformer that reduces the voltage from 220 to 6.3 V. The power of the transformer is small (20 mW), and the current consumption does not exceed 2-3 mA.

Working with the attachment. The terminals of the attachment 1, 2, 3 are connected to the corresponding terminals of the oscilloscope (Fig. 4).

Rice. 4. Connecting the set-top box with an oscilloscope.

The oscilloscope is switched to operating mode with external synchronization or sweep from external source. Connect the set-top box to the network. A horizontal line will appear on the screen (if pins 1 and 2 are not shorted). Then press the KH1 button, the line on the oscilloscope screen should deviate by a certain angle. Use the “Horizontal Gain”, “Vertical Gain” and “Vertical Gain” knobs to ensure that the line is located in the center of the screen at an angle of 45° to the horizontal axis. The length of the image should be equal to half the diameter of the screen (Fig. 5).

Rice. 5. Oscillograms obtained when testing electrical radio elements.

The element being tested is always connected to terminals 3 and 2 of the attachment. A vertical line on the screen (see Fig. 5) indicates a short circuit, a horizontal line indicates an open circuit or an open circuit in the element. The nature of the image on the oscilloscope screen is determined by the dependence of the resistance of the element under test on the magnitude and polarity of the sinusoidal voltage supplied to it.

Let's show what can be seen on the oscilloscope screen when examining the following elements.

Semiconductor diodes. The switching polarity and the appearance of the curves on the screen are shown in Fig. 5, a, b. When the diode is turned on in reverse, the curve shown in Fig. is obtained. 5, c. This way you can determine the anode and cathode terminals of diodes whose markings have been erased.

If the top of the corner on the screen is rounded, or one of its sides is much larger than the other, or the direction of the straight lines is very different from horizontal and vertical, then the diode should be rejected.

Zener diodes. If the stabilization voltage of the zener diode is less than 10 V, horizontal line a kink will appear (Fig. 5, d). The distance from the break to the vertical line will correspond to the stabilization voltage (in our case, 10 V).

Selenium valves. If the element is in working order, then the beam on the screen will draw a horizontal line, which smoothly turns into a vertical one (Fig. 5, e).

For a faulty element, the vertical part of the oscillogram will be very short or with a large slope. Such a curve indicates a large voltage drop across the valve when current flows in the forward direction. The voltage drop on selenium rectifiers is much greater than on germanium or silicon rectifiers.

Tunnel diodes. The connection method is shown in Fig. 5, e. The characteristics of a working diode are shown in the figure (curve 1). Sometimes, by increasing the horizontal gain, it is possible to obtain the pattern shown in the figure (curve 2), which is a typical characteristic of a tunnel diode. Before checking other parts, the “Horizontal Gain” knob must be moved to the position found during calibration.

Controlled valves (thyristors)(Fig. 5, g). The type of current-voltage characteristic for a serviceable element (with the control output disabled - CE) is shown in Fig. 5, f, 1. When the control electrode is connected to terminal 2, the thyristor opens and the beam draws a curve on the screen similar to the characteristic of a conventional diode connected in the conducting direction (Fig. 5, g, 2).

Transistors. Their connection to the console is shown in Fig. 5, h. If the emitter and collector pins are swapped, the pattern on the screen will not change (the base remains unconnected). The beam on the screen will draw a horizontal line, it may be slightly curved. Then connect the base to clamp 2 and obtain the characteristic shown in Fig. 5, h (1 - for pnp transistor, 2 - for like p-p-p). This is another way to determine the electrode terminals of unknown transistors. When switching the base output to terminal 3, the first waveform shown in Fig. 5, h, will correspond to the p-p-p transistor.

If, when testing transistors, a characteristic in the form of the letter L does not appear on the screen, this means that there is an open circuit in the transistor electrode circuit. When one of the oscillogram segments (letter L) is bent, this means that one of the r-n transitions transistor.

The bend of the vertical line indicates a high resistance in the forward direction, the slope of the horizontal line indicates a low reverse resistance of the junction (large reverse collector current). The deviation of the sides of the angle from the horizontal and vertical indicates poor quality transitions.

Typically, high-power transistors (even the best ones) always have a large reverse collector current. Therefore, you first need to test several serviceable powerful transistors and then use them as standards to check others. The phenomena indicating a short circuit or open circuit in a transistor are the same for all types of transistors.

Unijunction transistors. The connection diagram is shown in Fig. 5, k. First, the measurement should be carried out with the emitter turned off. A straight line with a slope of 30° relative to the horizontal axis should appear on the oscilloscope screen (Fig. 5, j, 1). Then connect the emitter to clamp 2, while part of the straight line on the screen should bend upward (Fig. 5, j, 2). If the emitter is connected to terminal 3 (to the base of the transistor), the lower end of the straight line will become vertical (Fig. 5, j, 3).

Resistors (fixed and variable). By measuring the angle of inclination of a straight line on the screen relative to the horizontal with a protractor, you can approximately determine the resistance values of various resistors. To do this, use the diagram in Fig. 5, l and the graph shown in Fig. 6. For resistors with a resistance of up to 100 ohms, the beam on the screen will draw a vertical axis, over 100 kOhm - a horizontal axis.

These two straight lines determine the measurement range of the oscilloscope. Before measurement, the resistor should be connected to terminals 3 and 2. One of the outer terminals and the middle terminal of the adjustable resistor (potentiometer) is connected to the attachment. When you rotate the axis of the variable resistor under study, the slope of the straight line on the screen should change. An unclear line image on the screen indicates contamination of the moving contact of the resistor.

Photoresistors connect to terminals 3 and 2. If the input hole of the photo controller is covered, a straight line with a small angle of inclination will appear on the screen. If the device is illuminated, a vertical line will appear. Using the graph shown in Fig. 6, you can determine the resistance of the device when illuminated with different intensities. This is how photoresistors with similar characteristics are selected, and photo exposure meters are also calibrated.

Rice. 6. Graph for determining the resistance value of fixed and variable resistors.

Capacitors of any type are also connected to terminals 3 and 2. For serviceable capacitors with a capacity of up to 0.85 μF, an ellipse with a horizontal major axis will appear on the screen (see Fig. 5, m). With a capacitance close to 0.85 µF, the screen will form a circle, and with a capacitance exceeding this value, an ellipse again, but with a large vertical axis. By measuring the ratio of the major and minor axes of the ellipse, you can use the graph shown in Fig. 7, find the approximate capacitance of the capacitor. If the major axis of the ellipse is tilted, this indicates that the capacitor leakage current is too high.

Rice. 7. Graph for finding the capacitances of the capacitors being tested.

Coils, relays and transformers. The terminals of the coils, relays and transformer windings are connected to terminals 3 and 2 of the console and the ellipse is observed on the oscilloscope screen. With a coil inductance of less than 5 G, the screen will display an ellipse, the major axis of which is slightly tilted relative to the vertical; with an inductance of 5 G, the screen will display a circle, and above 5 G, an ellipse will appear, the major axis of which is slightly deviated from the horizontal axis. Naturally, the accuracy of such measurements is not high, since the appearance of the oscillogram is affected not only by the inductance, but also by the capacitance of the windings. A waveform shape that differs from that described indicates a short circuit in the coil.

Given coils whose inductance is known, the measured inductance can be determined by comparison.

Checking electrical circuits. Since the device allows you to evaluate very small resistance values between terminals 3 and 2, it can be used to test switches, light bulbs, fuses, installation wires and electrical circuits.

Attachment to an oscilloscope for monitoring the characteristics of transistors
(characterist)

In Fig. 8, a shows a diagram of an attachment for observing the characteristics of transistors on the oscilloscope screen. Variable resistor R1 is designed to adjust the base current. A sheet of tracing paper is applied to the screen and the characteristic is traced. A typical collector junction characteristic is shown in Fig. 8, b. The vertical axis is the collector current, the horizontal axis is the collector voltage. The slope of the curve determines the saturation region. On the horizontal part of the curve, the operating point for the class A amplifier is selected. In Fig. 8, in addition to horizontal scan line 1, shows the characteristic of the reverse collector current at base current 1 equal to zero (curve 2), as well as output characteristics at base currents of 0.2 ... 1 mA. The characteristics obtained using an oscilloscope can be compared with those given in reference books.

Rice. 8. Attachment to an oscilloscope for monitoring the characteristics of transistors:
a - circuit diagram for transistors p-p-p, and for p-p-p the polarity of switching on elements B and D1 should be changed; b - main characteristic; c - family of characteristics.

Transistors designed to operate in push-pull cascades must have similar parameters. Our example shows a transistor structures p-p-p, included according to the OE scheme. You can also explore p-p-p transistor, appropriately connecting it to the console (in the OE, OB or OK circuits).

The article is compiled based on publications by V.G. Bastanova
Author-compiler. Patlakh V.V. 1999