July 03, 2023

Common faults and solutions for low current fiber optic transceivers

Common faults and solutions for low current fiber optic transceivers

Our widely used fiber optic transceivers have 6 indicators. What does each indicator mean? Does this mean that fiber optic transceiver is working properly if all indicators are lit?

PWR: Light on means 5V DC power supply is working properly;

FDX: LED on means fiber is transmitting data in full duplex mode;

FX 100: On indicates that fiber data rate is 100 Mbps;

TX 100: When indicator is on, it means that transmission rate of twisted pair is 100 Mbps, and when indicator is off, it means that transmission rate of twisted pair is 10 Mbps;

TX Link/Act: LED is always on, indicating that twisted pair connection is connected; LED flashes to indicate 10/100M data transmission over twisted pair.

If fiber optic transceiver is working properly, PWR power indicator should always be on, FX-LINK/ACT fiber link indicator and TX-LINK/ACT network link indicator should always be on or flashing if LINK/ACT indicator is off, you must check if corresponding channel is connected normally; As for FDX working mode indicator, FX-100 fiber speed indicator, and TX-100 network speed indicator, whether it is always on has no real effect on fiber optic transceiver.

1. Optical transceiver indicator light function and troubleshooting method

1. First, check if fiber optic transceiver or optical module LED and twisted pair port LED are lit?

  • A. If optical port indicator (FX-LINK/ACT) of transceiver is off, check that fiber link is correct cross-connect, fiber optic connector TX-RX, RX-TX.
  • B. If optical port LED (FXFX-LINK/ACT) of transceiver A is on and optical port LED (FXFX-LINK/ACT) of transceiver B is off, fault is transceiver A end: one This could be: optical transmission port of transceiver (TX)
  • It is defective because optical port (RX) of transceiver B cannot receive an optical signal; another possibility: transceiver optical transmitter (TX)
  • There is a problem with fiber optic connection at output (the optical cable or fiber optic jumper may be broken).
  • C. Twisted Pair LED (TXFX-LINK/ACT) is off. Please confirm if twisted pair is connected incorrectly or incorrectly?
  • Use a continuity tester to test (however, twisted pair LED on some transceivers will not turn on until fiber link is connected).
  • D. Some transceivers have two RJ45 ports: (to hub) indicates that connection line connected to switch is a direct line; (to
  • Node) indicates that trunk connecting switch is a crossover.
  • E. Some transceivers have an MPR switch: this means that connection line connected to switch is a direct method; DTE switch: connection
  • The connection line of switch is a crossover line.
  • 2. Are optical cables and jumpers broken?

  • A. Optical cable on-off detection: use a laser flashlight, sunlight or light to illuminate one end of optical cable connector or connector;
  • Is there visible light at other end? If there is visible light, it means that optical cable is not damaged.
  • B. Fiber link continuity detection: use laser flashlight, sunlight, etc. to illuminate one end of fiber jumper; look at other end.
  • Is there visible light? If there is visible light, it means that fiber optic jumper is not broken.
  • 3. Is half/full duplex mode incorrect?

    Some transceivers have side switches FDX: full duplex; HDX switches: half duplex mode.

    4. Detection with an optical power meter

    Light power of a fiber optic transceiver or optical module under normal conditions:

    Multimode 2 km: -10 dB to 18 dB;

    Single mode 20 km: -8 dB to 15 dB;

    60 km single mode: -5 dB to 12 dB;

    If light output of fiber optic transceiver is between -30dB and 45dB, then there is a problem with transceiver.

    2. Common mistakes and solutions

    Due to daily maintenance and user concerns, we hope to provide some assistance to maintenance personnel to determine cause of failure according to failure phenomenon, determine failure point, and "prescribe right medicine".

    1. When RJ45 port of transceiver is connected to other devices, which connection should be used?

    Reason: The RJ45 port of transceiver is connected to network card of PC (DTE data terminal equipment) with a crossed twisted pair cable, and connected to HUB or SWITCH (DCE data equipment) with a parallel cable.

    2. Why is TxLink LED not on?


  • 1. Connect wrong twisted pair cable.
  • 2. Poor contact between crystal head of twisted pair and equipment, or a quality problem of twisted pair cable itself.
  • 3. The device is not connected correctly.
  • 3. Why does TxLink LED not flash but stay on after a normal fiber connection?


  • 1. The malfunction is usually caused by too much transmission distance;
  • 2. Network card compatible (connectednoy to PC)
  • 4. Why is Fxlink indicator off?


  • 1. The fiber optic cable is not connected correctly. Correct connection method: TX-RX, RX-TX or incorrect fiber mode;
  • 2. The transmission distance is too long or intermediate loss is too large, exceeding rated loss of this product. Solution: take action to reduce
  • Intermediate loss can be replaced by a longer range transceiver.
  • 3. The operating temperature of fiber optic transceiver is too high.
  • 5. What is reason for Fxlink LED not flashing but staying on after a normal fiber connection?

    Reason: This error is usually caused by too long a transmission distance or too much intermediate loss, which exceeds rated loss of this product. The solution is to minimize intermediate losses or replace it with a transceiver with a longer transmission distance.

    6. What should I do if all five indicators are on, or indicators are normal, but transmission is not possible?

    Reason: Generally, turn off power and restart it to return to normal operation.

    7. What is ambient temperature of transceiver?

    Reason: The optical fiber module is highly affected by ambient temperature. Although it has a built-in automatic amplification circuit, when temperature exceeds a certain range, transmitted optical power of optical module is reduced, thereby degrading signal quality of optical network. Increase packet loss rate and even turn off optical link (typically, operating temperature of fiber optic module can reach 70°C)

    8. What is compatibility with external device protocols?


    10/100M fiber transceivers, like 10/100M switches, have certain frame length limits, typically no more than 1522B or 1536B. When switch connected to central office supports some special protocols (such as: Ciss ISL) increases packet overhead (Ciss ISL packet overhead is 30 bytes), which exceeds upper frame length limit of fiber optic transceiver and is discarded by it, reflecting high rate of loss or packet failure. At this time, you need to adjust terminal device MTU (MTU. The largest sending unit, total overhead of an IP packet is 18 bytes, and MTU is 1500 bytes. At present, high-end communication equipment manufacturers have internal network protocols and usually use separate packets, which will increase overhead of IP packets. If data is a 1500-word section, IP packet size will exceed 18 after IP packet is dropped), so that size of packet sent over line meets frame length limit network device.

    9. After chassand it worked fine for a while, why don't some cards work fine?


    The early chassis power supply uses relay mode. The main problems are insufficient power reserve of power supply and large losses in line. After chassis has been working normally for a while, some cards cannot work normally. When some cards are pulled out, rest of cards work normally. After chassis has been working for a long time work, connectors are oxidized and lead to a large loss of connectors. This type of power supply is out of specified range. If required range is exceeded, it may cause an abnormal phenomenon of inserting card into chassis. Powerful Schottky diodes are now used to protect isolation during chassis power switching, and connector shape has been improved to reduce power drop caused by control circuit and connector. At same time, power reserve of power supply is increased, which really makes backup power supply convenient and safe, and more suitable for requirement of long-term uninterrupted operation.

    10. What is function of communication signaling provided on transceiver?

    Cause: The transceiver has a link alarm function (channel loss). When a particular fiber is disconnected, it will automatically return to electrical port (i.e., LED on electrical port will also turn off). Reflected to switch's network management software. 3. Issues Needing Attention in Fiber Optic Transceivers

    1. Does optical transceiver support full duplex and half duplex?

    Some chips on market currently can only use full duplex media and cannot support half duplex. If they are connected to a switch (SWITCH) or hub (HUB) of another brand and use half-duplex mode , this is sure to cause serious collisions and packet loss.

    2. Have you tested connection with other fiber optic transceivers?

    There are more and more fiber optic transceivers on market these days. If compatibility of transceivers of different brands has not been tested in advance, there may be packet loss, long transmission time, sudden fast and slow transmission, etc.

    3. Is there a guard to prevent packet loss?

    When some manufacturers make fiber optic transceivers, they adopt Register mode to reduce cost. The biggest disadvantage of this method is unstable transmission and packet loss, and it is best to use buffer line design, which can safely avoid data packet loss.

    4. temperature adaptation?

    The fiber optic transceiver itself gets very hot during use. If temperature is too high (not higher than 50°C), it is important to consider when buying whether fiber optic transceiver works normally!