The working process of short wave transmitter needs high power DC and high voltage, and whether the transmitter is stable or not depends on this high power power power supply system. Whether the existing system can drive the whole machine to work is the key room control technology. This paper analyses the principle of PSM short wave transmitter modulator, and introduces the basic of PSM modulator of transmitter. The working process and the fault of PSM modulator of transmitter are analyzed theoretically. In the fault technical analysis, different phenomena but the same fault device are analyzed in detail. A series of summaries lay a foundation for future maintenance work. The PSM modulator is a circuit used to generate high terminal screen voltage and high terminal modulation voltage. It consists of two parts: one is a controller controller (1A8) that generates control signals, and the other is a high terminal screen modulation voltage composed of 48 stage power module and low pass filter. It is an important part of the high-cycle system of HF transmitter, which is related to the working efficiency of the tuning system and plays a key role in the normal operation of the broadcasting and transmitting equipment. At the same time, this part is also a major part of the high energy consumption of the transmitter room. In order to reduce energy consumption and improve the working state of the transmitter. TBH-522 150KW PSM short-wave transmitter belongs to bilateral band AM broadcasting transmitter. It is mainly for language or music broadcasting. The modulation mode is high-level AM with pulse step modulation (PSM). The transmitter combines the main power supply with the modulator. The working principle of short-wave transmitter is simply transmitter and exciter. The antenna and feeder together constitute the transmitting system. The current system can be distinguished according to the type of power tube used by the transmitter. One is the vacuum tube transmitter, the other is the all-solid-state transmitter. Vacuum tube transmitter has the advantages of high efficiency and low cost. Generally, high-power short-wave transmitter adopts this type. Its output power is fixed at a specific frequency, and the transmitter has a certain linearity. The output power of transmitter can be reduced by adjusting the output unit module. The transmitter is mainly composed of five parts: high cycle, low cycle, control, cooling and power supply. Low-cycle path: PSM is modulated by 48 power module, and audio signal is processed and amplified. Its function is to provide carrier power and sideband power to high weekend level. High-cycle path: It is mainly composed of high-front and high-end two-stage electronic tube tuning amplifier, which completes the matching between transmitter output and antenna feeder. It is the main path of high-frequency signal. Control system: The main function is to control the power supply of the transmitter by program.
When the transmitter is overloaded, it protects the transmitter. Cooling system: Air-cooled or water-cooled high-power devices to ensure their normal operation. Power supply system: consisting of primary and secondary power supply, primary power supply provides energy from outside to transmitter, secondary power supply is converted from primary power supply to various specifications of power supply, including various DC voltage stabilizer and rectifier power supply. In the low cycle modulation part, the low cycle is pulse step modulation (PSM). The transmitter combines the main power supply with the modulator, eliminates the main power supply and quantizes the DC plus audio signal in the modulator at equal intervals, then performs ring modulation (Fig. 1). The transmitter sends out control signals to 48 PSM power units, and adjusts the control finger according to the state signals sent back by each power unit. The principle is to turn the high-voltage rectifier into zero, control the voltage required by the high-end electronic tube into series power supply, and stack the supply voltage of a block of modules. The control of each power module is regulated by the audio control system, when the transmitter is running. When working, the access audio signal is modulated into digital signal by the audio control system to control the switches of each power module. In fact, all electronic switches are controlled by the audio carried, that is, the audio modulation voltage is indirectly superimposed on the output voltage. The EMI of DC power supply with PSM is smaller than that of PDM, the output spectrum is more regular and efficient, especially under light load. At the same time, the instantaneous response speed of PSM is faster than that of PDM, and the interference suppression ability is stronger. However, the output ripple of PSM is large, but it can be suppressed by optimization measures, so DC power supply of PSM mode is a good modulation mode. Fault phenomena: In the test machine, after coarse tuning into fine tuning, the front tuning, power meter can not afford, high and low end positive pressure, no positive current, thermostatic element the last curtain grille head hit the end. According to the power up/down, the voltage can not rise or decrease normally. The power meter can’t afford, the last stage of the positive pressure is very small, the curtain is used to set the head of the meter, and the power up/down is useless. The analysis should be the problem of the positive pressure caused by the less power module open. When we go to the side of the machine to observe, we find that most of the normal working lights of the 48 power module are not on. Investigate the audio modulation all the way, change the control circuit one by one, find out that after replacing the ring modulator, troubleshooting. The function of the ring modulator is to compare the number of switching on and off required by the A/D converter received with the number of switching on the unit. The digital level of the power switch is converted into an instruction signal to make the power module turn on or off. At the same time, the 48 power module is recycled to prolong the life of the module effectively. When a unit needs to be connected, the one with the longest disconnection time will be added. When a unit needs to be disconnected, the one with the longest disconnection time will be disconnected. If the number of connected units remains unchanged, the first one will be disconnected according to the triangular wave frequency (60HZ). The first one will be disconnected, and the first one will be disconnected. According to this rule, the first one will be disconnected. After replacing the ring modulator, the operation process of the whole machine is observed and returned to normal. Fault Phenomenon: In the test machine, once the high voltage is removed, the high-end curtain grid of the whole machine is too large and the high-end positive pressure is not available. The audio PSM channel is checked and replaced one by one. After replacing the A7 ring modulator, the whole machine returns to normal. Maintenance of the A7 board (Fig.
2): (1) Measuring the supply voltage ( 5V, 12V) is normal; (2) Measuring the pulse signal, normal input; (3) Discriminating circuit error, chip N3 can not normally output discriminating switch signal, each switch signal for 0.1V, the maximum value is 5V, that is, the corresponding 48 switches are closed, found that the output voltage has exceeded the normal value. As a result, the module switch control can not work properly, and the supply voltage of 11KV is not at all, so the high-end curtain grid is overloaded. Principle: Discriminant circuit is composed of error amplifier N3 (LM318).
Two legs of N3 are connected to the actual switch output summary signal. Three legs are the comparative signal from A/D converter board. Once three legs are larger than two legs, N3 outputs positive voltage and vice versa. When the two legs are equal, N3 outputs zero. Voltage comparator N1 is the discriminant circuit of switching and closing. Voltage comparator N2 It is the discriminant circuit of switch pull signal. Replace the error amplifier chip LM318, add the test machine again, and return to normal. Fault phenomena: In the test machine, after the tuning is normal, the audio test machine is added, and suddenly the whole machine drops off the high voltage. After recovery, the last positive current and positive pressure are zero. Observing by the machine, it is found that the normal output lamp of the 48 power module is not on and the input lamp is normal. The input lamp is normal, which indicates that the power supply voltage of the front 48 module is normal. It should be that the PSM tuning signal is not input into the 48 module. Drop the high voltage, pull off the PSM switch, check the control panels, are normal. Suspected to be a contact problem, the PSM channel plugs in the rear of the aircraft were re-inserted and re-inserted to restore normal. Audio channel signal is controlled by power control unit and then transformed into “audio direct current” with amplitude controlled. Then it is quantized at equal intervals in fast analog-to-digital converter, and then modulated by ring. The control signal of each power unit can be obtained. Finally, it is converted into optical control signal and sent to the corresponding power switching unit through optical fiber. After several failures, the whole PSM slot is replaced to solve the contact problem thoroughly. Fault Phenomenon: In the inverted frequency, after the tuning is normal, one plus audio, high-end positive voltage zero, high-end curtain grid current hit the watch head. The reason for this phenomenon should be that the module fails to work properly. After observation, the 48 power module is blocked completely as soon as it adds audio.
The front panel of the machine is observed. The third lamp of the A5 power control board is turned off and turned on (after adding audio), and it fails to work properly. The lamp is a PSM overcurrent signal lamp. Observing the whole positive and positive current is normal, the A5 board’s own problems are determined.
A5 display lamp: 1 lamp the input point is not used on the transmitter, the actual circuit is short-circuit; 2 lamp standing wave ratio is too large protection, when the transmitter appears too large standing wave ratio, from the protection unit of electronic control input low-level signal protection, normal not high-level signal; 3 lamp PSM over-current, when the modulator appears over-current, from the input and output board (1A8A11) When the transmitter is roughly tuned, the PSM part is blocked by this point. When the PSM part is blocked, the low-level signal is sent from the auto-tuning box (bright) and the high-level signal is sent when not blocked; 5 lights are not used, in fact, they are short-circuited; 6 lights are working instructions. The signal is the operation signal of the modulator, which outputs high level, blockades PSM and low level. Replace the power control board A5, test the transmitter, everything is back to normal. Fault Phenomenon: In the test machine, after the tuning is normal, once the audio frequency is added, the high-end positive current and positive pressure is full of the watch head, the high-end curtain gate rheology is reduced to 0.2A, the power is less than 20KW, and the external monitoring is on-load or off-regulation. Audio is not added, and the state returns to normal. After the tuning is completed, the audio is added and the fault is found. It shows that on the audio-added board, similar phenomena may occur in the modulation boards. Only the boards can be replaced sequentially. It is found that after replacing the A5 board, the fault will be removed. A5 power control board, with the control of lifting power, all require tuning to complete before work, the transmitter state positive voltage rises sharply, and related to lifting power. When D6C 9 feet are tuned, there is lifting power signal. Input high level makes E8 turn on, output low level signal. This low level signal makes D5B output high level to D6D 12 feet turn on all the way. Secondary pulse signal and V12 conduction make D5A 1 and 2 feet grounded, D5A 3 feet output high level through D6A, D5C, D6C output low level selected D10 tuning power electronic potentiometer. The fault of the signal causes the potentiometer to be in the command state of increasing power. After replacing the power control board A5, the whole machine is tested and everything is back to normal.
This paper introduces some common faults encountered by PSM modulator of TBH522 shortwave transmitter in the course of operation, as well as the analysis and treatment of these faults. It combines the operation principle of transmitter, the same faulty device, but different faults. It is very good for the on-duty maintenance personnel of TBH-522 shortwave transmitter. Learning and reference value.