Example 9: The machine has a receive launch indication, but the handheld receives no forward signal.
The cause of this failure may be the oscillating part of the emission, emitting the power amplifier and its control part. Using a tester to measure normal reception, measure its RF power to zero. Open the case, first test the TXPL L1TXVCO power supply is 8V, adjust TXVO, make TP2 4V, indicating that the transmit frequency oscillator is working properly. The fault is in the launch and control section. Observe that there are no obvious burnouts in some components of the power amplifier. Let the radio station be in the transmitting state and the +B power supply is normal. There is no T8 voltage. The reason may be that the power amplifier circuit does not work because there is no T8 voltage. From the circuit analysis, T8 voltage is output by IC2 and controlled by the 5-pin TR terminal of IC2. The TR terminal voltage is controlled by the 39-pin TR terminal of the front panel microprocessor IC1. When measured, 39 feet of IC1 have The voltage changes from 0 to 5V, and the 5-pin TR terminal of IC2 is always 13.5V. It is considered that Q1 is damaged. After switching to a good DTC114E or other similar transistor, T8 voltage is transmitted during the test, and the power is measured at 25W. The handset receives the forward signal.
Example 10: The radio forwards normally, but the local speaker does not ring.
First check that the plug P101 at the rear of the radio is intact. The cause of the failure is a malfunction of the horn or the squelch circuit. The horn was normal. Observed with an oscilloscope, there was no signal waveform at the input pin 1 of the audio amplifier IC1, and the signal at the 12-pin of the filter unit 29 was. The fault is the squelch signal added to Q9, Q10, resulting in no signal output and the local speaker does not ring. The mute signal is from the 8th pin of the IF unit 28, that is, the 14th pin of 28 types of IC1; the 14th pin is controlled by the change of the squelch voltage of IC1's 12 pin. In the actual measurement, when adjusting the SQL knob or receiving a signal, the IC pin 12 has a voltage change and the 14 pin voltage does not change. Q9, Q10 turn on the signal next to the road and the speaker silent. Since the radio is normally forwarded and only part of the circuit of IC1 is damaged, if the radio is used as a repeater station, it may be considered that there is no need to repair it. If you want to monitor or use it as a base station, you must replace IC1.
Example 11: The radio has power indication and cannot receive transmission.
The cause of this fault is very numerous and complex. When such a fault occurs, first check the frequency oscillation section to see if the power supply C8 of TXVCO, TXPLL, RXVCO, and RXPLL is 8V; then adjust RXVCO and TXVCO separately, and measure TP1 and TP2. Can it be adjusted between 0 and 8V, and it should be 4V when working. If the RXVCO/RXPLL and TXVCOTXPLL supply the C8 bit of 8V normally, and TP1 and TP2 cannot be adjusted to 4V, the chances of damage are small because the receiving and transmitting VCOs and phase-locked loops are separately enclosed in a metal box. First of all, there is no frequency data signal in the phase-locked loop. Check whether the microprocessor IC1 and frequency memory IC2 in the front panel are normal. In the actual maintenance process encountered the following situations.
1, TXPLLVCO, RXPLLVCO power supply C8, found to be 0V. Because there is no 8V operating voltage, the frequency oscillation part does not work. It is known from the circuit that the power supply of the TXPLLVCO is provided by the IC4; the power supply of the RXPLLVCO is provided by the IC2. The power supply is measured at 13.8V and its output is zero. IC4 is a three-terminal regulator block; IC2 is a power conversion module, which not only produces C8, but also R8 and T8 voltage conversion circuit. When repairing, replace with a good IC2 (MB3756) and IC4 (L7808). Adjusting RXTXVCO enables TP1 and TP2 to be tested with a handheld 4V and the radio resumes operation.
2. Measure the power of C8 is 8V, adjust RXTXVCO, and measure TP1 and TP2 cannot be adjusted to 4V to show that there is no frequency data signal in PLL. Use the KTP-20 writer to rewrite the frequency to the radio, and then test TP1 and TP2 still can not be adjusted to 4V microprocessor pin 58 of microprocessor IC1, and the voltage is 0. A closer inspection revealed that the R11 supply fuse resistor (22.2) was damaged. Replace with a good fuse resistor, TP1 and TP2 still can not be adjusted to 4V. I suspect there is a problem with IC1. Using the contrast method, the IC1 foot voltage of the radio station was found to be 2~3V for most of the foot voltage of the IC1 of the faulty machine, which is a lot different from the 5V of the normal radio station, and it is considered that the IC1 is damaged. Carefully weld the IC1, replace with a good MP75104G, rewrite the frequency, adjust the RXVCO, TXVCO, and make the TP1 and TP2 retest the radio at 4V. With the receive emission, the operation becomes normal.
3, measuring C8 is 8V normal, measuring TP1 and TP2 adjustment less than 4V. The KTP-20 is used to re-write the radio and the writer displays an error message. Suspected frequency memory IC2 is damaged. After replacing the 92C46 with a good one, the frequency is rewritten, the frequency meter shows normal, the RXVCO, TXVCO are adjusted, and the TP1 and TP2 are 4V. The radio receives transmission and resumes.
4, measuring C8 were 8V normal, measuring micro-processing IC1 foot voltage is normal, adjust RXVCO, TXVCO, measured TP1 and TP2 can not be adjusted to 4V, write frequency instrument re-write frequency, write frequency meter display normal, adjust RXVCO, TXVCO can make TP1 and TP2 as 4V, measure and receive and launch, everything returns to normal. The reason is that the frequency data stored in IC2 is lost due to transient voltage surges, and transmission cannot be received. If this fault occurs frequently, replace IC2 with a good 92C46.
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