TKR-720/820 base/transmission station, compact structure, good shielding performance. The whole machine is divided into five parts, namely DC voltage regulator circuit, display unit circuit, transmit and receive main circuit, small-signal processing unit and post-stage power amplifier circuit. Under normal circumstances, the aircraft rarely fails, in the actual maintenance process, often in the following two cases of failure, one is the power supply voltage instability, including the power supply voltage rise and lightning induced high voltage grid; Second, the antenna Being struck by a lightning, the antenna senses its current. During the overhaul, it mainly grasps the following two points.
First of all, separate the DC voltage regulator section from the next stage and check whether the DC output is 13.8V. After checking, supply power to other parts.
Second, according to the phenomenon of failure, determine the approximate scope of the fault. After the scope is determined, the most important point is also that the main point of the machine overhaul is to check whether the DC operating voltage of each component is normal. The main voltage test points include the output of IC4 in the display unit; whether the 58-pin of IC1 is 5V; The test points TP1, TP2, IC4, and IC2 of the voltage controlled oscillator in the cell, and the voltage transitions of Q1, Q8 in the display unit, and IC2 in the main board are normal, and so on. Under normal circumstances, according to the presence of voltage, coupled with the detection of other instruments, can be troubleshooting.
Example 1: The TKR-820 radio is struck by lightning without any indication.
Open the lid and find that the 1.6A AC fuse is blown (the glass tube has collapsed), the power transformer T101 is burned, and the key components are inspected with a three-meter meter. It is found that the D101 bridge rectifier cone has been punctured and other components are normal. After replacing the 1.6A fuse, transformer and bridge rectifying cone, unplug the 13.8V output plug and check the continuity test. Then try to adjust the output current of the dummy load to 6A for 30 minutes without exception, and troubleshoot the power supply. The 13.8V output plug is connected, and the boot test is still not displayed. After looking up the sending and receiving unit along the power supply circuit, it was found that the K1 internal current limit switch was blown, because the 1A fuse was not used as a substitute for this component. After power on, the power indicator lighted but no transceiver was available. Open the front panel inspection display unit found that the middle part of the microprocessor IC1 (model number 75104G) cracked due to a lightning strike, and the power supply pin (pin 58) was short-circuited to ground without voltage. Checking the external components found that the fuse resistance R11 was open circuit, so the microprocessing was concluded. IC1 is damaged. After replacing IC1 and R11 with a well-grounded 30W pin type soldering iron, the voltage of each pin of IC1 is checked normally, and the technical indicators of transmission and reception detection and debugging are fully restored to normal.
Example 2: When the TKR-820 radio is struck by lightning, the power indicator light is on, but no transceiver is available.
The appearance inspection found that the receiving indicator was always on, and the volume potentiometer was adjusted to provide no noise. Turn on the machine and check the sending and receiving two voltage controlled oscillators in the sending unit. The voltages at the test points TP1 and TP2 are 0V, and the adjustment trimmer capacitor is invalid (it can change between 0-8V in normal conditions). The unit's power supply circuit was then investigated and it was found that both the IC4 model number 78N08 and IC2 model number MB3756 were damaged. Then IC4 was replaced, but when preparing to replace IC2, it was inconvenient because neither this piece nor the technical data of the component was on hand. According to the drawings, the working principle of MB3756 is analyzed, and it is found that the integrated block is controlled by the microprocessor IC1 on the display unit, where pin 1 is 8.1V output; pin 2 is powered by 13.8V; pin 3 is connected to 47 μF capacitor, 4 Foot grounding; 5 feet for the control foot, usually 13.8V, launch 0V; 6 feet 8.3V, 0V when launched; 7 feet are empty feet; 8 feet is 0V, launch 8.3V. Based on this, we designed a circuit using the LM7808, 3DK4, and 3DG238, fixed in the empty box on the back of the terminal (amplifier) ​​unit (be sure to pay attention to heat), solder the NB3756, and connect the leads to the points according to the figure check number. The power test returned to normal. The machine has been used continuously for more than a year after being repaired and has been working normally.
Example 3: The TKR-820 radio does not display power and the connection replacement fuse is blown.
Open the machine using open circuit method to check the power supply circuit, and found that the power circuit of the terminal (amplifier) ​​unit is short-circuited to the ground. Further inspection revealed that the power amplifier integrated block IC1 model M57729H has been broken down. After the IC1 is replaced, the power-on power indicator is on and the receiver is normal. When the transmitter is on, the indicator light is on. The 13.8V supply current is 4A (proving the power amplifier integrated block) but no power output. Using a frequency meter, short-time emission (within 0.5 seconds) is measured step by step from the interface of the transmitting antenna, and when the pin 5 of the IC1 of the power amplifier is detected, an output is found. The power-off checked one by one between IC1 pin 5 and the transmitting antenna interface, and found that L11 was severely scorched and other components were normal. Replace the windings with the enameled wire in the L11 style, and troubleshoot.
Example 4: Can receive the transmission, the radio can't receive the call of the long distance mobile phone; But the mobile phone can receive the signal of the base station.
According to the above fault phenomenon, it is considered that the transmission of the base station is normal and the failure is in the receiving part. First eliminate the reason for receiving the antenna, the fault persists. Fault In the high-frequency amplification section, the AH5403 tester was used to input high-frequency signals to the radio and found that the receiver sensitivity was only +60 dBμ. First adjust the L7, L9, L10, no significant change in sensitivity. The height measuring and discharging tube Q3 is normal, and there is no abnormality in measuring other elements. Finally, the high frequency signal is directly supplied to the Q3 base, and the sensitivity returns to normal. Then the signal is directly supplied to the RXIN point, and the sensitivity is also normal. Description There is a disconnection from the antenna base to the circuit board. Through the observation, there are two sections of cable lines from the antenna base to the circuit board, which are measured by a multimeter. Among them, the section near the circuit board is broken. According to the user, the aircraft transceiver uses an antenna, which causes the fault after a lightning strike. The reason is that when a lightning strikes, the current induced by the receiving antenna blows the cable. During repair, because the cable is special, another good coaxial cable can be directly soldered to the circuit board.
Example 5: The TKR-820 radio relay function does not work.
Check the aircraft in the relay state, the transmission indicator does not light; but in the duplex working state using the microphone launch but there is emission power output. Unscrew the front panel and check the Q8 on the display unit along the transmit key PTT. It is found that there is no 5V voltage at the C pole of the Q8, and the Q8 is checked under welding, in which the CE poles have been punctured. After the trial transistor 9012 is connected between a BE pole and a B pole to the 39th pin of the microprocessor IC1 (model 75104G), a 3 KΩ resistor is substituted for the Q8, and the relay station returns to normal.
Taizhou TS HARDWARE Co., Ltd , https://www.shuwengroup.com