Many specialists, and especially radio amateurs, are well aware of the S1-94 oscilloscope (Fig. 1). The oscilloscope, with its rather good technical characteristics, has very small dimensions and weight, as well as a relatively low cost. Thanks to this, the model immediately gained popularity among specialists involved in mobile repair of various electronic equipment, which does not require a very wide bandwidth of input signals and the presence of two channels for simultaneous measurements. Currently, a fairly large number of such oscilloscopes are in operation.
In this regard, this article is intended for specialists who need to repair and configure the S1-94 oscilloscope. The oscilloscope has a block diagram common for devices of this class (Fig. 2). It contains a vertical deflection channel (VDO), a horizontal deflection channel (HTO), a calibrator, an electron beam indicator with a high-voltage power supply, and a low-voltage power supply.
The CVO consists of a switchable input divider, a preamplifier, a delay line, and a final amplifier. It is designed to amplify the signal in the frequency range of 0...10 MHz to the level required to obtain the specified vertical deviation coefficient (10 mV/div...5 V/div in steps of 1-2-5), with minimum amplitude frequency and phase-frequency distortions.
The CCG includes a timing amplifier, a timing trigger, a trigger circuit, a sweep generator, a blocking circuit, and a sweep amplifier. It is designed to provide linear beam deflection with a specified sweep factor from 0.1 µs/div to 50 ms/div in 1-2-5 steps.
The calibrator generates a signal to calibrate the instrument in terms of amplitude and time.
The CRT assembly consists of a cathode ray tube (CRT), a CRT power circuit, and a backlight circuit.
The low-voltage source is designed to supply all functional devices with voltages of +24 V and ±12 V.
Consider the operation of the oscilloscope at the circuit level.
The investigated signal through the input connector Ш1 and the push-button switch V1-1 ("Open / Closed input") is fed to the input switchable divider on the elements R3 ... R6, R11, C2, C4 ... C8. The input divider circuit ensures that the input resistance is constant regardless of the position of the vertical sensitivity switch B1 ("V / DIV."). Divider capacitors provide frequency compensation of the divider over the entire frequency band.
From the output of the divider, the signal under study is fed to the input of the KVO preamplifier (block U1). A source follower for a variable input signal is assembled on a field-effect transistor T1-U1. For direct current, this stage provides symmetry of the operating mode for subsequent stages of the amplifier. The divider on resistors R1-Y1, Ya5-U1 provides an input impedance of the amplifier equal to 1 MΩ. Diode D1-U1 and zener diode D2-U1 provide input protection against overloads.
The two-stage preamplifier is made on transistors T2-U1 ... T5-U1 with a common negative feedback (OOS) through R19-Y1, R20-Y1, R2-Y1, R3-Y1, C2-U1, Rl, C1, which allows get an amplifier with the required bandwidth, which practically does not change with a step change in the stage gain by two and five times. Changing the gain is carried out by changing the resistance between the emitters of transistors UT2-U1, VT3-U1 by switching resistors R3-y 1, R16-yi and Rl in parallel with the resistor R16-yi. The amplifier is balanced by changing the potential of the base of the transistor TZ-U1 with a resistor R9-yi, which is brought out under the slot. The beam is shifted vertically by resistor R2 by changing the base potentials of transistors T4-U1, T5-U1 in antiphase. The correcting chain R2-yi, C2-U1, C1 performs frequency correction of the gain depending on the position of switch B1.1.
To delay the signal relative to the start of the sweep, a delay line L31 is introduced, which is the load of the amplifying stage on transistors T7-U1, T8-U1. The output of the delay line is included in the base circuits of the transistors of the final stage, assembled on transistors T9-U1, T10-U1, T1-U2, T2-U2. This inclusion of the delay line ensures its coordination with the cascades of the preliminary and final amplifiers. Frequency correction of the gain is performed by the chain R35-yi, C9-U1, and in the final amplifier stage - by the chain C11-U1, R46-yi, C12-U1. Correction of the calibrated values of the deviation coefficient during operation and change of the CRT is carried out by the resistor R39-yi, brought out under the slot. The final amplifier is assembled on transistors T1-U2, T2-U2 according to a common base circuit with a resistive load R11-Y2 ... R14-Y2, which allows you to achieve the required bandwidth of the entire vertical deflection channel. From the collector loads, the signal is fed to the vertical deflecting plates of the CRT.
The signal under study from the KVO preamplifier circuit through the emitter follower cascade on the T6-U1 transistor and switch V1.2 is also fed to the input of the KGO synchronization amplifier for synchronous start of the sweep circuit.
The synchronization channel (US block) is designed to start the sweep generator synchronously with the input signal to obtain a still image on the CRT screen. The channel consists of an input emitter follower on a T8-UZ transistor, a differential amplification stage on T9-UZ, T12-UZ transistors, and a synchronization trigger on T15-UZ, T18-UZ transistors, which is an asymmetric trigger with emitter coupling with an emitter follower on input on the transistor T13-U2.
The D6-UZ diode is included in the base circuit of the T8-UZ transistor, which protects the synchronization circuit from overloads. From the emitter follower, the clock signal is fed to the differential amplification stage. The differential stage switches (B1-3) the polarity of the synchronizing signal and amplifies it to a value sufficient to trigger the synchronization trigger. From the output of the differential amplifier, the clock signal is fed through the emitter follower to the input of the synchronization trigger. A signal normalized in amplitude and shape is removed from the collector of the T18-UZ transistor, which, through the decoupling emitter follower on the T20-UZ transistor and the differentiating circuit S28-UZ, Ya56-U3, controls the operation of the trigger circuit.
To increase the synchronization stability, the synchronization amplifier, together with the synchronization trigger, is powered by a separate 5 V voltage regulator on a T19-UZ transistor.
The differentiated signal is fed to the trigger circuit, which, together with the sweep generator and the blocking circuit, provides the formation of a linearly changing sawtooth voltage in standby and self-oscillating modes.
The trigger circuit is an asymmetric emitter-coupled trigger on transistors T22-UZ, T23-UZ, T25-UZ with an emitter follower at the input on the T23-UZ transistor. The initial state of the trigger circuit: the T22-UZ transistor is open, the T25-UZ transistor is open. The potential to which the C32-UZ capacitor is charged is determined by the collector potential of the T25-UZ transistor and is approximately 8 V. The D12-UZ diode is open. With the arrival of a negative pulse at the T22-UZ base, the trigger circuit is inverted, and the negative drop on the T25-UZ collector locks the D12-UZ diode. The trigger circuit is disconnected from the sweep generator. The formation of the forward stroke of the sweep begins. The sweep generator is in standby mode (switch B1-4 in the "WAITING" position). When the amplitude of the sawtooth voltage reaches about 7 V, the trigger circuit through the blocking circuit, transistors T26-UZ, T27-UZ returns to its original state. The recovery process begins, during which the time-setting capacitor C32-UZ is charged to the initial potential. During recovery, the blocking circuit maintains the trigger circuit in its original state, preventing the synchronization pulses from transferring it to another state, that is, it delays the start of the sweep by the time necessary to restore the sweep generator in standby mode and automatically starts the sweep in self-oscillating mode. In the self-oscillatory mode, the sweep generator operates in the "AWT" position of the switch B1-4, and the launch and disruption of the operation of the trigger circuit - from the blocking circuit by changing its mode.
As a sweep generator, a circuit for discharging a time-setting capacitor through a current stabilizer was chosen. The amplitude of the linearly changing sawtooth voltage generated by the sweep generator is approximately 7 V. The time-setting capacitor C32-UZ during recovery is quickly charged through the T28-UZ transistor and the D12-UZ diode. During the working stroke, the D12-UZ diode is locked by the control voltage of the trigger circuit, disconnecting the timing capacitor circuit from the trigger circuit. The capacitor is discharged through the T29-UZ transistor, which is connected according to the current stabilizer circuit. The discharge rate of the time-setting capacitor (and, consequently, the value of the sweep factor) is determined by the current value of the T29-UZ transistor and changes when the time-setting resistances R12 ... R19, R22 ... R24 are switched in the emitter circuit using switches B2-1 and B2- 2 ("TIME/DIV."). The sweep speed range has 18 fixed values. A change in the sweep factor by a factor of 1000 is provided by switching the time-setting capacitors C32-UZ, S35-UZ with the switch Bl-5 ("mS / mS").
Setting the sweep coefficients with a given accuracy is carried out by the SZZ-UZ capacitor in the "mS" range, and in the "mS" range - by a tuning resistor R58-y3, by changing the mode of the emitter follower (transistor T24-UZ), which supplies the timing resistors. The blocking circuit is an emitter detector based on a T27-UZ transistor, connected according to a common emitter circuit, and on R68-y3, S34-UZ elements. A sawtooth voltage is supplied to the input of the blocking circuit from the divider R71-y3, R72-y3 at the source of the transistor TZO-UZ. During the working stroke of the sweep, the capacitance of the S34-UZ detector is charged synchronously with the sweep voltage. During the recovery of the sweep generator, the transistor T27-UZ is closed, and the time constant of the emitter circuit of the detector R68-y3, C34-UZ maintains the control circuit in its original state. The standby sweep mode is provided by locking the emitter follower on the T26-UZ switch V1-4 ("WAITING / AUTO."). In the self-oscillating mode, the emitter follower is in a linear mode of operation. The time constant of the blocking circuit is changed in steps by switch B2-1 and coarsely by B1-5. From the sweep generator, the sawtooth voltage is fed through the source follower on the TZO-UZ transistor to the sweep amplifier. The repeater uses a field-effect transistor to increase the linearity of the sawtooth voltage and eliminate the influence of the input current of the sweep amplifier. The sweep amplifier amplifies the sawtooth voltage to a value that provides a given sweep ratio. The amplifier is made as a two-stage, differential, cascode circuit on transistors TZZ-UZ, T34-UZ, TZ-U2, T4-U2 with a current generator on the transistor T35-UZ in the emitter circuit. The frequency correction of the gain is carried out by the capacitor C36-UZ. To improve the accuracy of time measurements, the CVO of the device provides for a sweep stretch, which is provided by changing the gain of the sweep amplifier by connecting resistors Y75-U3, R80-UZ in parallel when contacts 1 and 2 ("Stretching") of the ShZ connector are closed.
Table 1. MODES OF ACTIVE ELEMENTS ON DIRECT CURRENT
| Designation |
Voltage, V |
||
| Collector, stock | emitter, source | Base, shutter | |
|
Amplifier U1 |
|||
| T1 | 8,0-8,3 | 0,6-1 | 0 |
| T2 | -(3,8-5,0) | 1,3-1,8 | 0,6-1,2 |
| TK | -(3,8-5,0) | 1,3-1,8 | 0,6-1,2 |
| T4 | -(1,8-2,5) | -(4,5-5,5) | -(3,8-5,0) |
| T5 | -(1,8-2,5) | -(4,5-5,5) | -(3,8-5,0) |
| T6 | -(11,3-11,5) | -(1,3-1,9) | -(1,8-2,5) |
| T7 | 0,2-1,2 | -(2,6-3,4) | -(1,8-2,5) |
| T8 | 0,2-1,2 | -(2,6-3,4) | -(1,8-2,5) |
| T9 | 6,5-7,8 | 0-0,7 | 0,2-1,2 |
| T1O | 6,5-7,8 | 0-0,7 | 0,2-1,2 |
|
Amplifier U2 |
|||
| T1 | 60-80 | 8,3-9,0 | 8,8-9,5 |
| T2 | 60-80 | 8,3-9,0 | 8,8-9,5 |
| TK | 100-180 | 11,0-11,8 | 11,8-12,3 |
| T4 | 100-180 | 11,0-11,8 | 11,8-12,3 |
|
Ultrasonic sweep |
|||
| T1 | -(11-9) | 12 | 13,5-14,5 |
| T2 | -(11-9) | 12 | 13,5-14,5 |
| TK | -(10,5-11,5) | -(10,1-11,1) | -(11,0-10,4) |
| T4 | -(18-23) | -(8,2-10,2) | -(8,5-10,5) |
| T6 | -(14,5-17) | -(8-10,2) | -(8-10,5) |
| T7 | 6-6,5 | 0 | 0-0,2 |
| T8 | 4,5-5,5 | -(0,5-0,8) | 0 |
| T9 | 4,5-5,5 | -(0,7-0,9) | -(0,6-0,8) |
| T1O | -(11,4-11,8) | 0 | -(0,6-0,8) |
| T12 | 0,5-1,5 | -(0,6-0,8) | 0 |
| T13 | 4,5-5,5 | 3,7-4,8 | 4,5-5,6 |
| T14 | -(12,7-13) | -0.3 to 2.0 | -1 to 1.5 |
| T15 | 3,0-4,2 | 3,0-4,2 | 3,6-4,8 |
| T16 | -(25-15,0) | -12 | -(12,0-12,3) |
| T17 | -(25-15) | -(12,0-12,3) | -(12,6-13) |
| T18 | 4,5-5,5 | 3,0-4,1 | 2,0-2,6 |
| T19 | 7,5-8,5 | 4,5-5,5 | 5,2-6,1 |
| T2O | -12 | 5,1-6,1 | 4,5-5,5 |
| T22 | 0,4-1 | -0.2 to 0.2 | 0,5-0,8 |
| T23 | 12 | -0.3 to 0.3 | 0,4-1 |
| T24 | -12 | -(9,6-11,3) | -(10,5-11,9) |
| T25 | 8,0-8,5 | -0.2 to 0.2 | -0.2 to 0.2 |
| T26 | -12 | -0.2 to 0.2 | 0,3-1,1 |
| T27 | -12 | 0,3-1,1 | -0.2 to 0.4 |
| T28 | 11,8-12 | 7,5-7,8 | 8,0-8,5 |
| T29 | 6,8-7,3 | -(0,5-0,8) | 0 |
| TZO | 12 | 7,3-8,3 | 6,8-7,3 |
| T32 | 12 | 6,9-8,1 | 7,5-8,8 |
| TZZ | 10,6-11,5 | 6,1-7,6 | 6,8-8,3 |
| T-34 | 10,6-11,5 | 6,1-7,4 | 6,8-8,1 |
| T35 | -(4,8-7) | -(8,5-8,9) | -(8,0-8,2) |
The amplified sweep voltage is removed from the collectors of the transistors ТЗ-У2, Т4-У2 and fed to the horizontally deflecting plates of the CRT.
The synchronization level is changed by changing the potential of the base of the T8-UZ transistor by the resistor R8 ("LEVEL"), displayed on the front panel of the device.
The beam is shifted horizontally by changing the base voltage of the T32-UZ transistor with resistor R20, which is also displayed on the front panel of the device.
The oscilloscope has the ability to supply an external synchronization signal through socket 3 ("Output X") of the ShZ connector to the T32-UZ emitter follower. In addition, a sawtooth voltage output of about 4 V is provided from the emitter of the TZZ-UZ transistor to slot 1 ("Output N") of the ShZ connector.
The high-voltage converter (block U31) is designed to power the CRT with all the necessary voltages. It is assembled on transistors T1-U31, T2-U31, transformer Tpl and is powered by stabilized +12V and -12V sources, which allows you to have stable CRT supply voltages when the mains voltage changes. The supply voltage of the CRT cathode -2000 V is removed from the secondary winding of the transformer through the doubling circuit D1-U31, D5-U31, S7-U31, S8-U31. The supply voltage of the CRT modulator is also removed from the other secondary winding of the transformer through the multiplication circuit D2-U31, DZ-U31, D4-U31, SZ-U31, S4-U31, S5-U31. To reduce the influence of the converter on the power sources, an emitter follower ТЗ-У31 was used.
The CRT filament is powered from a separate winding of the Tpl transformer. The supply voltage of the first anode of the CRT is removed from the resistor Ya10-U31 ("FOCUSING"). The brightness of the CRT beam is controlled by the resistor R18-Y31 ("BRIGHTNESS"). Both resistors are brought to the front panel of the oscilloscope. The supply voltage of the second anode of the CRT is removed from the resistor Ya19-U2 (brought out under the slot).
The backlight circuit in the oscilloscope is a symmetrical trigger, powered from a separate 30 V source relative to the -2000 V cathode power source, and is made on transistors T4-U31, T6-U31. The trigger is triggered by a positive pulse taken from the emitter of the transistor T23-UZ of the trigger circuit. The initial state of the backlight trigger T4-U31 is open, T6-U31 is closed. A positive edge of the pulse from the trigger circuit switches the backlight trigger to another state, a negative one returns it to its original state. As a result, a positive pulse with an amplitude of 17 V is formed on the T6-U31 collector, equal in duration to the duration of the forward sweep. This positive pulse is applied to the CRT modulator to illuminate the forward sweep.
The oscilloscope has the simplest amplitude and time calibrator, which is made on the T7-UZ transistor and is an amplifier circuit in the limiting mode. The input of the circuit receives a sinusoidal signal with the frequency of the power supply. Rectangular pulses are taken from the collector of the T7-UZ transistor with the same frequency and amplitude of 11.4 ... 11.8 V, which are fed to the input divider KVO in position 3 of switch B1. In this case, the sensitivity of the oscilloscope is set to 2 V / div, and the calibration pulses should occupy five divisions of the vertical scale of the oscilloscope. Timebase calibration is performed in position 2 of switch B2 and position "mS" of switch B1-5.
The voltages of the 100 V and 200 V sources are not stabilized and are taken from the secondary winding of the power transformer Tpl through the doubling circuit DS2-UZ, S26-UZ, S27-UZ. The source voltages of +12 V and -12 V are stabilized and are obtained from a stabilized 24 V source. The 24 V stabilizer is made on transistors T14-UZ, T16-UZ, T17-UZ. The voltage at the input of the stabilizer is removed from the secondary winding of the transformer Tpl through the diode bridge DS1-UZ. The adjustment of the stabilized voltage of 24 V is carried out by the Y37-U3 resistor, brought out under the slot. To obtain sources of +12 V and -12 V, an emitter follower T10-UZ is included in the circuit, the base of which is powered by a resistor R24-y3, which adjusts the +12 V source.
When carrying out repairs and subsequent tuning of the oscilloscope, first of all, it is necessary to check the modes of active elements for direct current for compliance with their values \u200b\u200bgiven in Table. 1. If the checked parameter does not fit within the allowable limits, it is necessary to check the serviceability of the corresponding active element, and if it is serviceable, the "strapping" elements in this cascade. When replacing the active element with a similar one, it may be necessary to adjust the operation mode of the cascade (if there is an appropriate tuning element), but in most cases this is not necessary, because. the cascades are covered by negative feedback, and therefore the spread of the parameters of the active elements does not affect the normal operation of the device.
In the event of malfunctions associated with the operation of the cathode ray tube (poor focusing, insufficient beam brightness, etc.), it is necessary to check the compliance of the voltages at the CRT terminals with the values \u200b\u200bgiven in Table. 2. If the measured values do not correspond to the table values, it is necessary to check the serviceability of the nodes responsible for the generation of these voltages (high voltage source, output channels of the KVO and KTO, etc.). If the voltages supplied to the CRT are within the permissible range, then the problem is in the tube itself, and it must be replaced.
Table 2. DC CRT MODES
Notes:
- Checking the modes given in table. 2 (except contacts 1 and 14) is made relative to the instrument case.
- Checking the modes on contacts 1 and 14 of the CRT is carried out relative to the cathode potential (-2000 V).
- Operating modes may differ from those indicated in Table. 1 and 2 by ±20%.
Zakharychev E.V., design engineer
The differentiated signal is fed to the trigger circuit, which, together with the sweep generator and the blocking circuit, provides the formation of a linearly changing sawtooth voltage in standby and self-oscillating modes.
The trigger circuit is an asymmetric emitter-coupled trigger on transistors T22-UZ, T23-UZ, T25-UZ with an emitter follower at the input on the T23-UZ transistor. The initial state of the trigger circuit: the T22-UZ transistor is open, the T25-UZ transistor is open. The potential to which the C32-UZ capacitor is charged is determined by the collector potential of the T25-UZ transistor and is approximately 8 V. The D12-UZ diode is open. With the arrival of a negative pulse at the T22-UZ base, the trigger circuit is inverted, and the negative drop on the T25-UZ collector locks the D12-UZ diode. The trigger circuit is disconnected from the sweep generator. The formation of the forward stroke of the sweep begins. The sweep generator is in standby mode (switch B1-4 is in the “WAITING” position). When the amplitude of the sawtooth voltage reaches about 7 V, the trigger circuit through the blocking circuit, transistors T26-UZ, T27-UZ returns to its original state. The recovery process begins, during which the time-setting capacitor C32-UZ is charged to the initial potential. During recovery, the blocking circuit maintains the trigger circuit in its original state, preventing the synchronization pulses from transferring it to another state, that is, it delays the start of the sweep by the time necessary to restore the sweep generator in standby mode and automatically starts the sweep in self-oscillating mode. In the self-oscillating mode, the sweep generator operates in the “AWT” position of the switch B1-4, and the launch and disruption of the operation of the trigger circuit - from the blocking circuit by changing its mode.
As a sweep generator, a circuit for discharging a time-setting capacitor through a current stabilizer was chosen. The amplitude of the linearly changing sawtooth voltage generated by the sweep generator is approximately 7 V. The time-setting capacitor C32-UZ during recovery is quickly charged through the T28-UZ transistor and the D12-UZ diode. During the working stroke, the D12-UZ diode is locked by the control voltage of the trigger circuit, disconnecting the timing capacitor circuit from the trigger circuit. The capacitor is discharged through the T29-UZ transistor, which is connected according to the current stabilizer circuit. The discharge rate of the time-setting capacitor (and, consequently, the value of the sweep factor) is determined by the current value of the T29-UZ transistor and changes when the time-setting resistances R12 ... R19, R22 ... R24 are switched in the emitter circuit using switches B2-1 and B2- 2 ("TIME / DIV."). The sweep speed range has 18 fixed values. A change in the sweep factor by a factor of 1000 is provided by switching the time-setting capacitors C32-UZ, S35-UZ with a switch V1-5 (“mS / mS”).
Setting the sweep coefficients with a given accuracy is carried out by the SZZ-UZ capacitor in the "mS" range, and in the "mS" range - by a tuning resistor R58-y3, by changing the mode of the emitter follower (transistor T24-UZ), which supplies the timing resistors.
The blocking circuit is an emitter detector based on a T27-UZ transistor, connected according to a common emitter circuit, and on R68-y3, S34-UZ elements. A sawtooth voltage is supplied to the input of the blocking circuit from the divider R71-y3, R72-y3 at the source of the transistor TZO-UZ. During the working stroke of the sweep, the capacitance of the S34-UZ detector is charged synchronously with the sweep voltage. During the recovery of the sweep generator, the transistor T27-UZ is closed, and the time constant of the emitter circuit of the detector R68-y3, C34-UZ maintains the control circuit in its original state. The standby sweep mode is provided by locking the emitter follower on the T26-UZ with the V1-4 switch ("WAITING / AUTO"). In the self-oscillating mode, the emitter follower is in a linear mode of operation. The time constant of the blocking circuit is changed in steps by switch B2-1 and coarsely by B1-5. From the sweep generator, the sawtooth voltage is fed through the source follower on the TZO-UZ transistor to the sweep amplifier. The repeater uses a field-effect transistor to increase the linearity of the sawtooth voltage and eliminate the influence of the input current of the sweep amplifier. The sweep amplifier amplifies the sawtooth voltage to a value that provides a given sweep ratio. The amplifier is made as a two-stage, differential, cascode circuit on transistors TZZ-UZ, T34-UZ, TZ-U2, T4-U2 with a current generator on the transistor T35-UZ in the emitter circuit. The frequency correction of the gain is carried out by the capacitor C36-UZ. To improve the accuracy of time measurements, the CVO of the device provides for a sweep stretch, which is provided by changing the gain of the sweep amplifier by connecting resistors 1175-UZ, R80-UZ in parallel when contacts 1 and 2 (“Stretching”) of the ShZ connector are closed.
The amplified sweep voltage is removed from the collectors of the transistors ТЗ-У2, Т4-У2 and fed to the horizontally deflecting plates of the CRT.
The synchronization level is changed by changing the potential of the base of the T8-UZ transistor by the resistor R8 (“LEVEL”), displayed on the front panel of the device.
The beam is shifted horizontally by changing the base voltage of the transistor T32-UZ resistor R20 ("<->”), displayed also on the front panel of the device.
The oscilloscope has the ability to supply an external synchronization signal through slot 3 ("Output X") of the ShZ connector to the T32-UZ emitter follower. In addition, a sawtooth voltage output of about 4 V is provided from the emitter of the TZZ-UZ transistor to socket 1 ("Output "Ch"") of the ShZ connector.
The high-voltage converter (block U31) is designed to power the CRT with all the necessary voltages. It is assembled on transistors T1-U31, T2-U31, transformer Tpl and is powered by stabilized +12V and -12V sources, which allows you to have stable CRT supply voltages when the mains voltage changes. The supply voltage of the CRT cathode -2000 V is removed from the secondary winding of the transformer through the doubling circuit D1-U31, D5-U31, S7-U31, S8-U31. The supply voltage of the CRT modulator is also removed from the other secondary winding of the transformer through the multiplication circuit D2-U31, DZ-U31, D4-U31, SZ-U31, S4-U31, S5-U31. To reduce the influence of the converter on the power sources, an emitter follower ТЗ-У31 was used.
The CRT filament is powered from a separate winding of the Tpl transformer. The supply voltage of the first anode of the CRT is removed from the resistor 1110-U31 (“FOCUSING”). The brightness of the CRT beam is controlled by the resistor Ш8-У31 (“BRIGHTNESS”). Both resistors are brought to the front panel of the oscilloscope. The supply voltage of the second anode of the CRT is removed from the resistor Ш9-У2 (brought out under the slot).
The backlight circuit in the oscilloscope is a symmetrical trigger, powered from a separate 30 V source relative to the -2000 V cathode power source, and is made on transistors T4-U31, T6-U31. The trigger is triggered by a positive pulse taken from the emitter of the transistor T23-UZ of the trigger circuit. The initial state of the backlight trigger T4-U31 is open, T6-U31 is closed. A positive edge of the pulse from the trigger circuit switches the backlight trigger to another state, a negative one returns it to its original state. As a result, a positive pulse with an amplitude of 17 V is formed on the T6-U31 collector, equal in duration to the duration of the forward sweep. This positive pulse is applied to the CRT modulator to illuminate the forward sweep.
| MODES OF ACTIVE ELEMENTS ON DIRECT CURRENT | |||
| Designation | Voltage, V | ||
| Collector, stock | emitter, source | Base, shutter | |
| Amplifier U1 | |||
| T1 | 8,0-8,3 | 0,6-1 | 0 |
| T2 | -(3,8-5,0) | 1,3-1,8 | 0,6-1,2 |
| TK | -(3,8-5,0) | 1,3-1,8 | 0,6-1,2 |
| T4 | -(1,8-2,5) | -(4,5-5,5) | -(3,8-5,0) |
| T5 | -(1,8-2,5) | -(4,5-5,5) | -(3,8-5,0) |
| T6 | -(11,3-11,5) | -(1,3-1,9) | -(1,8-2,5) |
| T7 | 0,2-1,2 | -(2,6-3,4) | -(1,8-2,5) |
| T8 | 0,2-1,2 | -(2,6-3,4) | -(1,8-2,5) |
| T9 | 6,5-7,8 | 0-0,7 | 0,2-1,2 |
| T10 | 6,5-7,8 | 0-0,7 | 0,2-1,2 |
| Amplifier U2 | |||
| T1 | 60-80 | 8,3-9,0 | 8,8-9,5 |
| T2 | 60-80 | 8,3-9,0 | 8,8-9,5 |
| TK | 100-180 | 11,0-11,8 | 11,8-12,3 |
| T4 | 100-180 | 11,0-11,8 | 11,8-12,3 |
| Ultrasonic sweep | |||
| T1 | -(11-9) | 12 | 13,5-14,5 |
| T2 | -(11-9) | 12 | 13,5-14,5 |
| TK | -(10,5-11,5) | -(10,1-11,1) | -(11,0-10,4) |
| T4 | -(18-23) | -(8,2-10,2) | -(8,5-10,5) |
| T6 | -(14,5-17) | -(8-10,2) | -(8-10,5) |
| T7 | 6-6,5 | 0 | 0-0,2 |
| T8 | 4,5-5,5 | -(0,5-0,8) | 0 |
| T9 | 4,5-5,5 | -(0,7-0,9) | -(0,6-0,8) |
| T10 | -(11,4-11,8) | 0 | -(0,6-0,8) |
| T12 | 0,5-1,5 | -(0,6-0,8) | 0 |
| T13 | 4,5-5,5 | 3,7-4,8 | 4,5-5,6 |
| T14 | -(12,7-13) | -0.3 to 2.0 | -1 to 1.5 |
| T15 | 3,0-4,2 | 3,0-4,2 | 3,6-4,8 |
| T16 | -(25-15,0) | -12 | -(12,0-12,3) |
| T17 | -(25-15) | -(12,0-12,3) | -(12,6-13) |
| T18 | 4,5-5,5 | 3,0-4,1 | 2,0-2,6 |
| T19 | 7,5-8,5 | 4,5-5,5 | 5,2-6,1 |
| T20 | -12 | 5,1-6,1 | 4,5-5,5 |
| T22 | 0,4-1 | -0.2 to 0.2 | 0,5-0,8 |
| T23 | 12 | -0.3 to 0.3 | 0,4-1 |
| T24 | -12 | -(9,6-11,3) | -(10,5-11,9) |
| T25 | 8,0-8,5 | -0.2 to 0.2 | -0.2 to 0.2 |
| T26 | -12 | -0.2 to 0.2 | 0,3-1,1 |
| T27 | -12 | 0,3-1,1 | -0.2 to 0.4 |
| T28 | 11,8-12 | 7,5-7,8 | 8,0-8,5 |
| T29 | 6,8-7,3 | -(0,5-0,8) | 0 |
| TZO | 12 | 7,3-8,3 | 6,8-7,3 |
| T32 | 12 | 6,9-8,1 | 7,5-8,8 |
| TZZ | 10,6-11,5 | 6,1-7,6 | 6,8-8,3 |
| T-34 | 10,6-11,5 | 6,1-7,4 | 6,8-8,1 |
| T35 | -(4,8-7) | -(8,5-8,9) | -(8,0-8,2) |
The voltages of the 100 V and 200 V sources are not stabilized and are taken from the secondary winding of the power transformer Tpl through the doubling circuit DS2-UZ, S26-UZ, S27-UZ. The source voltages of +12 V and -12 V are stabilized and are obtained from a stabilized 24 V source. The 24 V stabilizer is made on transistors T14-UZ, T16-UZ, T17-UZ. The voltage at the input of the stabilizer is removed from the secondary winding of the transformer Tpl through the diode bridge DS1-UZ. The adjustment of the stabilized voltage of 24 V is carried out by the resistor R37-y3, brought out under the slot. To obtain sources of +12 V and -12 V, an emitter follower T10-UZ is included in the circuit, the base of which is powered by a resistor R24-y3, which adjusts the +12 V source.
When carrying out repairs and subsequent tuning of the oscilloscope, first of all, it is necessary to check the modes of active elements for direct current for compliance with their values \u200b\u200bgiven in Table. 1. If the parameter being checked does not fit within the allowable limits, it is necessary to check the serviceability of the corresponding active element, and if it is serviceable, the “strapping” elements in this cascade. When replacing the active element with a similar one, it may be necessary to adjust the operation mode of the cascade (if there is an appropriate tuning element), but in most cases this is not necessary, because. the cascades are covered by negative feedback, and therefore the spread of the parameters of the active elements does not affect the normal operation of the device.
In the event of malfunctions associated with the operation of the cathode ray tube (poor focusing, insufficient beam brightness, etc.), it is necessary to check the compliance of the voltages at the CRT terminals with the values \u200b\u200bgiven in Table. 2. If the measured values do not correspond to the table values, it is necessary to check the serviceability of the nodes responsible for the generation of these voltages (high voltage source, output channels of the KVO and KGO, etc.). If the voltages supplied to the CRT are within the permissible range, then the problem is in the tube itself, and it must be replaced.
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Due to its small size and low cost, the oscilloscope C1-94 especially suitable for electronic radio repair services, as well as for radio amateurs and educational institutions.
Many specialists, and especially radio amateurs, are well aware of the S1-94 oscilloscope. The oscilloscope, with its rather good technical characteristics, has very small dimensions and weight, as well as a relatively low cost. Thanks to this, the model immediately gained popularity among specialists involved in mobile repair of various electronic equipment, which does not require a very wide bandwidth of input signals and the presence of two channels for simultaneous measurements.
Main technical characteristics of the S1-94 device:
Bandwidth: 0-10 MHz.
Rise time RH: 35 ns.
Deviation factor: 10 mV/div - 5 V/div.
The limits of the basic error of the coefficients of deviation and sweep: ± 6%.
Sweep ratio: 0.1 µs/div - 50 ms/div.
Input impedance, capacitance:
1 MΩ, 40 pF;
10 MΩ, 25 pF (with remote divider 1:10).
Indicator type: CRT 8LO7I.
The working part of the screen: 40x60 mm.
Power: 220±22V, 50±0.5Hz or 240±24V, 60±0.6Hz.
Power consumption: 25 V*A.
This article is intended for specialists who need to repair and configure the S1-94 oscilloscope. The oscilloscope has a typical block diagram for devices of this class. It contains a vertical deflection channel (CVO), a horizontal deflection channel (CGO), a calibrator, an electron beam indicator with a high-voltage power supply, and a low-voltage power supply.
The simplified block diagram does not show only two power supplies of a high-voltage source that generates high voltage for a cathode ray tube (CRT) and a low-voltage one for the operation of all other nodes, and there is also no built-in calibrator designed to set up the oscilloscope before taking measurements.
The signal under test enters the “Y” input of the vertical deflection channel and then follows the attenuator, which is nothing more than a multi-position switch that adjusts the sensitivity threshold. Its scale is graduated in Volt/cm or Volt/div. One division of the coordinate grid on the CRT display is implied. The values are also marked there: 0.1 V, 10 V, 100 V. If we do not know the approximate amplitude of the signal under study, then we set the minimum sensitivity, 100 volts per division.
The oscilloscope kit includes dividers 1:10 and 1:100, which are cylindrical and rectangular nozzles with connectors. They are used for the same purpose as an attenuator, and in the case of measurements with short pulses, they compensate for the capacitance of the coaxial cable. The figure below shows an external divider to the S1-94 oscilloscope. His, division ratio is 1 to 10.
Thanks to this attachment, you can significantly expand the capabilities of the device, since when using it, you can investigate signals with a much larger amplitude of hundreds of volts. From the output of the divider, the signal follows to the preamplifier. It then forks and goes to the delay line and sync switch. The delay line is necessary to compensate for the response time of the horizontal scan generator with the measured signal entering the vertical deflection amplifier. The final amplifier is designed to form the voltage going to the “Y” plates and sets the deflection of the vertical beam.
The sweep generator is needed to generate a sawtooth voltage following the horizontal deflection amplifier and the “X” plates and provides a horizontal deflection of the beam. It is equipped with a switch, graduated time per division ("Time/div"), and a sweep time scale.
The timing device starts the sweep generator in parallel with the appearance of the signal at the start point of the display. As a result, on it we observe the image of the pulse unfolded in time. The synchronization switch is equipped with the following ranges: Synchronization from the signal under test; Synchronization from the network; Synchronization from an external source. In amateur radio practice, the first band is most often used.
The CCG includes a timing amplifier, a timing trigger, a trigger circuit, a sweep generator, a blocking circuit, and a sweep amplifier. It is designed to provide linear beam deflection with a specified sweep factor from 0.1 µs/div to 50 ms/div in 1-2-5 steps.
The calibrator generates a signal to calibrate the instrument in terms of amplitude and time. The CRT assembly consists of a cathode ray tube (CRT), a CRT power circuit, and a backlight circuit. The low-voltage source is designed to power all functional devices with voltages of +24 V and ±12 V. Let's consider the operation of the oscilloscope at the circuit diagram level. The investigated signal through the input connector Ш1 and the push-button switch V1-1 (“Open / Closed input”) is fed to the input switchable divider on the elements R3 ... R6, R11, C2, C4 ... C8. The input divider circuit ensures that the input resistance is constant regardless of the position of the vertical sensitivity switch B1 (“V / DIV.”). Divider capacitors provide frequency compensation of the divider over the entire frequency band.
From the output of the divider, the signal under study is fed to the input of the KVO preamplifier (block U1). A source follower for a variable input signal is assembled on T1-U1. For direct current, this stage provides symmetry of the operating mode for subsequent stages of the amplifier. The divider on resistors R1-y1, R5-y1 provides an input impedance of the amplifier equal to 1MΩ. Diode D1-U1 and zener diode D2-U1 provide input protection against overloads.
The two-stage preamplifier is made on transistors T2-U1 ... T5-U1 with a common negative feedback (OOS) through R19-y1, R20-y1, R2-y1, R3-y1, C2-U1, R1, C1, which allows get an amplifier with the required bandwidth, which practically does not change with a step change in the stage gain by two and five times.
Changing the gain is carried out by changing the resistance between the emitters of transistors VT2-y1, VT3-U1 by switching resistors R3-y1, R16-y1 and R1 in parallel with the resistor R16-y1. The amplifier is balanced by changing the potential of the base of the transistor T3-U1 by the resistor R9-y1, which is brought out under the slot. The beam is shifted vertically by resistor R2 ("Z") by changing the base potentials of transistors T4-U1, T5-U1 in antiphase.
This inclusion of the delay line ensures its coordination with the cascades of the preliminary and final amplifiers. Frequency gain correction is performed by the R35-y1, C9-y1 chain, and in the final amplifier stage - by the C11-y1, R46-y 1, C12-y1 chain. Correction of the calibrated values of the deviation coefficient during operation and change of the CRT is carried out by the resistor R39-y1, brought out under the slot. The final amplifier is assembled on transistors T1-U2, T2-U2 according to a common base circuit with a resistive load Sh1-U2 ... R14-y2, which allows you to achieve the required bandwidth of the entire vertical deflection channel.
From the collector loads, the signal is fed to the vertical deflecting plates of the CRT. The signal under study from the KVO preamplifier circuit through the emitter follower cascade on the T6-U1 transistor and switch V1.2 is also fed to the input of the KGO synchronization amplifier for synchronous start of the sweep circuit. The synchronization channel (block U3) is designed to start the sweep generator synchronously with the input signal to obtain a still image on the CRT screen. The channel consists of an input emitter follower on transistor T8-U3, a differential amplification stage on transistors T9-U3, T12-U3 and a synchronization trigger on transistors T15-U3, T18-U3, which is an asymmetric trigger with emitter coupling with an emitter follower on input on the transistor T13-U2. The diode D6-U3 is included in the base circuit of the transistor T8-U3, which protects the synchronization circuit from overloads. From the emitter follower, the clock signal is fed to the differential amplification stage.
In the differential stage, switching (B 1-3) of the polarity of the synchronizing signal is carried out and it is amplified to a value sufficient to trigger the synchronization trigger. From the output of the differential amplifier, the clock signal is fed through the emitter follower to the input of the synchronization trigger. A signal normalized in amplitude and shape is removed from the collector of the transistor T18-U3, which, through the decoupling emitter follower on the transistor T20-U3 and the differentiating circuit C28-U3, R56-Y3, controls the operation of the start-up circuit. To increase the synchronization stability, the synchronization amplifier, together with the synchronization trigger, is powered by a separate 5 V voltage regulator on the T19-U3 transistor. The differentiated signal is fed to the trigger circuit, which, together with the sweep generator and the blocking circuit, provides the formation of a linearly changing sawtooth voltage in standby and self-oscillating modes.
The trigger circuit is an asymmetric emitter-coupled flip-flop on transistors T22-y3, T23-y3, T25-y3 with an emitter follower at the input on transistor T23-y3. The initial state of the trigger circuit: the transistor T22-y3 is open, the transistor T25-y3 is open. The potential to which the capacitor C32-U3 is charged is determined by the potential of the collector of the transistor T25-y3 and is approximately 8 V. The diode D12-U3 is open. With the arrival of a negative pulse at the T22-y3 base, the trigger circuit is inverted, and the negative drop on the T25-y3 collector locks the D12-U3 diode. The trigger circuit is disconnected from the sweep generator. The formation of the forward stroke of the sweep begins.
The sweep generator is in standby mode (switch B1-4 is in the “WAITING” position). When the sawtooth voltage amplitude reaches about 7 V, the trigger circuit through the blocking circuit, transistors T26-U3, T27-y3 returns to its original state. The recovery process begins, during which the time-setting capacitor C32-U3 is charged to the initial potential. During recovery, the blocking circuit maintains the trigger circuit in its original state, preventing the synchronization pulses from transferring it to another state, that is, it delays the start of the sweep by the time necessary to restore the sweep generator in standby mode and automatically starts the sweep in self-oscillating mode.
In the self-oscillating mode, the sweep generator operates in the “AWT” position of the switch B1-4, and the launch and disruption of the operation of the trigger circuit - from the blocking circuit by changing its mode. As a sweep generator, a circuit for discharging a time-setting capacitor through a current stabilizer was chosen. The amplitude of the linearly changing sawtooth voltage generated by the sweep generator is approximately 7 V. The time-setting capacitor C32-U3 during recovery is rapidly charged through the transistor T28-U3 and the diode D12-U3. During the working stroke, the D12-U3 diode is locked by the control voltage of the trigger circuit, disconnecting the timing capacitor circuit from the trigger circuit. The capacitor is discharged through the T29-U3 transistor, which is connected according to the current stabilizer circuit. The discharge rate of the timing capacitor (and, consequently, the value of the sweep factor) is determined by the current value of the transistor T29-U3 and changes when switching the timing resistances R12 ... R19, R22 ... R24 in the emitter circuit using switches B2-1 and B2- 2 ("TIME / DIV."). The sweep speed range has 18 fixed values.
A change in the sweep factor by a factor of 1000 is provided by switching the time-setting capacitors C32-U3, C35-U3 with a switch V1-5 (“mS / mS”). Setting the sweep coefficients with a given accuracy is carried out by the capacitor C33-U3 in the "mS" range, and in the "mS" range - by the tuning resistor R58-y3, by changing the mode of the emitter follower (transistor T24-U3), which supplies the timing resistors. The blocking circuit is an emitter detector on a transistor T27-U3, connected according to a common emitter circuit, and on elements R68-y3, C34-U3.
A sawtooth voltage is supplied to the input of the blocking circuit from the divider R71-y3, R72-y3 at the source of the transistor T30-U3. During the working stroke of the sweep, the capacitance of the C34-U3 detector is charged synchronously with the sweep voltage. During the recovery of the sweep generator, the transistor T27-U3 is turned off, and the time constant of the emitter circuit of the detector R68-y3, C34-U3 maintains the control circuit in its original state. The standby sweep mode is provided by locking the emitter follower on T26-U3 with switch V1-4 (“WAITING / AUT.”). In the self-oscillating mode, the emitter follower is in a linear mode of operation. The time constant of the blocking circuit is changed in steps by switch B2-1 and coarsely by B1-5.
From the sweep generator, the sawtooth voltage is fed through the source follower on the T30-U3 transistor to the sweep amplifier. The repeater uses a field-effect transistor to increase the linearity of the sawtooth voltage and eliminate the influence of the input current of the sweep amplifier. The sweep amplifier amplifies the sawtooth voltage to a value that provides a given sweep ratio. The amplifier is made two-stage, differential, according to the cascode circuit on transistors T33-U3, T34-U3, T3-U2, T4-U2 with a current generator on the transistor T35-U3 in the emitter circuit. The frequency correction of the gain is carried out by the capacitor C36-U3. To improve the accuracy of time measurements, the CVO of the device provides for a sweep stretch, which is provided by changing the gain of the sweep amplifier by connecting resistors R75-Y3, R80-U3 in parallel when contacts 1 and 2 (“Stretching”) of the Sh3 connector are closed.
The amplified sweep voltage is removed from the collectors of transistors T3-U2, T4-U2 and fed to the horizontally deflecting plates of the CRT.
Changing the synchronization level is done by changing the potential of the base of the transistor T8-U3 by the resistor R8 ("LEVEL"), displayed on the front panel of the device.
The beam is shifted horizontally by changing the base voltage of the T32-U3 transistor with a resistor R20 ("^"), also displayed on the front panel of the device.
The oscilloscope has the ability to supply an external synchronization signal through socket 3 (“X output”) of connector Ш3 to the T32-U3 emitter follower. In addition, a sawtooth voltage output of about 4 V is provided from the emitter of the T33-U3 transistor to socket 1 (“Output N”) of the Sh3 connector.
The high-voltage converter (block U31) is designed to power the CRT with all the necessary voltages. It is assembled on transistors T1-U31, T2-U31, transformer Tr1 and is powered by stabilized +12V and -12V sources, which allows you to have stable CRT supply voltages when the mains voltage changes. The supply voltage of the CRT cathode -2000 V is removed from the secondary winding of the transformer through the doubling circuit D1-U31, D5-U31, S7-U31, S8-U31. The supply voltage of the CRT modulator is also removed from the other secondary winding of the transformer through the multiplication circuit D2-U31, D3-U31, D4-U31, S3-U31, S4-U31, S5-U31. To reduce the influence of the converter on the power sources, an emitter follower T3-U31 was used.
The CRT filament is powered from a separate winding of the transformer Tr1. The supply voltage of the first anode of the CRT is removed from the resistor R10-y31 (“FOCUSING”). The brightness of the CRT beam is controlled by the resistor R18 ^ 31 ("BRIGHTNESS"). Both resistors are brought to the front panel of the oscilloscope. The supply voltage of the second anode of the CRT is removed from the resistor R19-U2 (brought out under the slot).
The backlight circuit in the oscilloscope is a symmetrical trigger, powered from a separate 30 V source relative to the -2000 V cathode power source, and is made on transistors T4-U31, T6-U31. The trigger is triggered by a positive pulse taken from the emitter of the transistor T23-U3 of the trigger circuit. The initial state of the backlight trigger T4-U31 is open, T6-U31 is closed. A positive edge of the pulse from the trigger circuit switches the backlight trigger to another state, a negative one returns it to its original state. As a result, a positive pulse with an amplitude of 17 V is formed on the T6-U31 collector, equal in duration to the duration of the forward sweep. This positive pulse is applied to the CRT modulator to illuminate the forward sweep.
The oscilloscope has the simplest amplitude and time calibrator, which is made on the T7-U3 transistor and is an amplifier circuit in the limiting mode. The input of the circuit receives a sinusoidal signal with the frequency of the power supply. From the collector of the transistor T7-U3, rectangular pulses are taken with the same frequency and amplitude of 11.4 ___ 11.8 V, which are fed to the input divider of the KVO in position 3 ("Ў") of switch B1. In this case, the sensitivity of the oscilloscope is set to 2 V / div, and the calibration pulses should occupy five divisions of the vertical scale of the oscilloscope. The sweep factor calibration is performed in position 2 of switch B2 and position "mS" of switch B1-5.
The voltage sources of 100 V and 200 V are not stabilized and are taken from the secondary winding of the power transformer Tr1 through the doubling circuit DS2-U3, S26-U3, S27-U3. The source voltages + 12 V and -12 V are stabilized and are obtained from a stabilized 24 V source. The 24 V stabilizer is made on transistors T14-U3, T16-U3, T17-U3. The voltage at the input of the stabilizer is removed from the secondary winding of the transformer Tr1 through the diode bridge DS1-U3. The adjustment of the stabilized voltage of 24 V is carried out by the resistor Ш7-У3, brought out under the slot. To obtain sources of +12 V and -12 V, an emitter follower T10-U3 is included in the circuit, the base of which is powered by a resistor R24-Y3, which adjusts the +12 V source.
When carrying out repairs and subsequent tuning of the oscilloscope, first of all, it is necessary to check the modes of active elements for direct current for compliance with their values \u200b\u200bgiven in Table. 1. If the parameter being checked does not fit within the allowable limits, it is necessary to check the serviceability of the corresponding active element, and if it is serviceable, the “strapping” elements in this cascade. When replacing the active element with a similar one, it may be necessary to adjust the operation mode of the cascade (if there is an appropriate tuning element), but in most cases this is not necessary, because. the cascades are covered by negative feedback, and therefore the spread of the parameters of the active elements does not affect the normal operation of the device.
In the event of malfunctions associated with the operation of the cathode ray tube (poor focusing, insufficient beam brightness, etc.), it is necessary to check the compliance of the voltages at the CRT terminals with the values \u200b\u200bgiven in Table. 2. If the measured values do not correspond to the table values, it is necessary to check the serviceability of the nodes responsible for the generation of these voltages (high voltage source, output channels of the KVO and KGO, etc.). If the voltages supplied to the CRT are within the permissible range, then the problem is in the tube itself, and it must be replaced.
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