Common Troubleshooting of Optical Receivers
The failures of the optical receiver can be roughly divided into three categories: one is the failure of the power supply, the other is the failure of the optical cable routing, and the third is the failure of the optical equipment. These three parts are connected with each other in the entire optical transmission system. No matter which part fails, it will cause the optical station to have no signal, or sometimes no signal, and the signal is very low. The following is the analysis and treatment of some common faults;
Fault 1: Users below the optical station sometimes report signals that sometimes do not exist.
Analysis and processing; first, check the power supply situation, check the 220V power supply point to the 60V power supply, and the power supply to the optical receiver. All connectors in this section of the line must be carefully checked. When a connector has a slight poor contact, it may occur Ignition produces an oxygen layer, increases the contact resistance, and then causes the optical receiver to work intermittently. At this time, even if the signal is working, the quality is very poor. Secondly, check the grounding of the optical station. If there is no grounding or the grounding is poor, or it is too close to the exposed wire, after a long period of accumulation, strong static electricity will also accumulate on the steel strand, which will also cause signal failure in the optical station. Now and then.
Fault 2: The power supply of the optical station is normal, but the output signal is very low or there is no signal.
Analysis and processing; when encountering this situation, first ask about the signal conditions of other optical stations carried by the front-end optical transmitter. If the signal of other optical stations is also very low or there is no signal, then check the transmitter in the computer room and the working status of the front-end equipment , if the front-end equipment is normal, it is necessary to inspect the optical cable route from the branch point of the optical station to the front-end to see if it is damaged by the outside. If the optical cable routing environment is very complicated, or the underground pipeline is laid, it cannot be inspected visually, and it is necessary to use testing instruments to judge. For example; use the breakpoint detection function of OTDR to find the actual position of the breakpoint and troubleshoot.
Fault 3, the optical station has output, but the signal is low.
Analysis and processing; detection from the front end to the optical station, according to the graph after OTDR detection, find the actual position of the optical cable with large attenuation on the graph, and check whether there is a ring diameter of the nearby optical cable caused by the line being hit or hooked become smaller, and even the fiber optic cable has been twisted. This failure generally only needs to restore the optical cable to its original state, and the signal can return to normal.
Fault 4, the optical receiver has no RF output.
Analysis and processing; After checking the optical hair, routing, and power supply lines are normal, it is necessary to check the optical receiver itself. First of all, turn on the optical receiver to see if there is any water ingress, and if there is any burning smell. Because, when the optical receiver enters or infiltrates water, as the temperature inside and outside the machine changes, small water droplets will form inside the machine, which can easily cause a short circuit on the circuit board and cause sparks to occur. At this time, there will be occasional signals, and after a period of time, the electronic components will burn out, and there will be no signal at all. Then check the optical receiving power and the photoelectric conversion situation. The TR series optical receiver has an alarm indicator for optical input signal loss. When the light is on, it means that the input power is lower than -6.5dBm. Use a multimeter to test the input power value of the optical input signal at 5V/mW. Next, check the power supply in the optical receiver. Sometimes the optical receiving module works normally, but the electrical signal amplifying module does not work, because the DC line supplying the amplifying module is faulty. This type of failure is often caused by the DC connection between the upper and lower parts being crushed when the casing is fastened, or the casing screws are not tightened, and the water enters and short-circuits and burns out the circuit.
Fault 5, the output level of the optical receiver is low.
Analysis and processing; three situations may occur when the output level of the optical receiver is low;
[1] Both high and low end signals are poor. The main reasons for this kind of failure are; 1. Poor contact or dirt of the optical fiber APC head; 2. The resistance of the gain adjustment potentiometer or insert becomes larger or the quality is not good; 3. The performance of the amplifier module deteriorates.
[2] The high-end signal is normal, and the low-end signal is poor. The main reason for this phenomenon is poor contact caused by oxidation and corrosion of the output port, gain, and balance adjustment plug-in. And due to the open circuit of the equalization device.
[3] The low-end signal is normal, and the high-end signal is poor. The main reasons are: the performance of the amplifier module is poor, the Q value of the high-frequency magnetic core device decreases, and the internal components of the optical machine are affected by moisture. The airtightness of the field-type optical receiver should be checked frequently to prevent the intrusion of rainwater.
Fault 6, the output signal of the optical receiver produces mutual modulation and moiré interference.
Analysis and processing; the reason is that the internal gain is too high, the output level is overloaded, the decoupling capacitor is open or invalid, and the shielding is bad. It can be done by replacing the balance insert, and the decoupling capacitor. If it is invalid, the amplifier module needs to be replaced.
Fault 7, the output level of the optical receiver is unstable.
Analysis and treatment: Most of the causes of this kind of failure are loose plug-ins and poor contact. The solder joints of some related components are weak, unsoldered, voltage regulator block, amplifier module, gain plug-in and related resistance-capacitance components have poor performance, unstable work, etc., causing the output signal to fluctuate.
Fault 8: After the optical receiver is struck by lightning, the output level is low.
Analysis and processing; when the outside line is struck by lightning, it usually causes damage to the power supply of the optical receiver. The parts that are easily damaged are lightning arrester, transformer, filter capacitor, voltage regulator block and other components. The fault causing the low output level is signal channel blockage or short circuit. Check the output level of the photoelectric conversion module BGE887BO. When the input optical power is -1dB (1310nm), the level should be around 70dB. After equalization and attenuation, the input power Amplifying module BGY785A, the level of the output pin of the amplifying module is 98dB, connected to the F seat through the distribution output, removed the core board, and found that the connection line between the output F seat and the distribution network has been burnt, and the distribution coil insulation has been burnt and short circuited. Rewind the distribution coil, solder the breakpoint of the circuit board, and the optical machine works back to normal.
Fault 9, the output signal of the optical receiver is unstable and changes irregularly.
Analysis and processing; first check the light-emitting and light-receiving equipment. Eliminate the cause of the device. According to the user survey, after a strong wind, this phenomenon of ups and downs often occurs. According to the analysis of the situation; the fault point is more likely to be on the splice box. Checking along the line, it is found that there is a hanging splicing box that swings a lot when the wind is strong. Opening and checking, it is found that the clips that press the cable in the box are loose, the optical cable can rotate, the optical fiber is out of the slot, and is wound on the central fixing screw. As the optical cables at both ends of the box rotate, the optical fiber wrapped on the central screw stretches and changes like a spring, and the force attenuation of the optical fiber increases to cause signal instability. Re-press the optical cable and reel the optical fiber, and the output level of the optical machine is normal.
