- Networks
- Fibre routers
LOS
Digi LOS on fibre router: optical signal loss or low power
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
The LOS indicator on your Digi fibre router is on: optical signal is lost or received power is too low. Check the fibre cable is firmly connected to the PON port and the wall socket, and never look into the connector end.
Safety first
Stop and check this first
- The reset button returns the router to factory values if held for at least 5 seconds; do not use it for LOS without talking to Digi first, because you will lose your settings.
- Do not open the router casing or look into the fibre connector to see if light comes out: Digi's manual advises against it because of eye risk and electrical safety.
Safe checks you can perform
- LOS and PON status
- Fibre cable at the PON port and the wall socket
- Turn the router off and on
- Report the fault to Digi
Leave these tasks to a qualified professional
- Do not attempt this professional task: Check registration with the OLT
- Do not attempt this professional task: Measure received optical power
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Check registration with the OLT
What they doDigi checks on its network whether the router registers with the OLT, which is what the PON indicator reflects.
In writingwhether registration is restored and what was changed to achieve it.
Measure received optical power
What they doThe operator's technician uses an optical power meter at the wall socket and the router and compares the reading with the receiver sensitivity.
They must show youthe reading against the specified value.
In writingwhere the signal is lost and what was repaired.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
LOS and PON status
- Who:
- you.
- How:
- look at the front of the router: note whether LOS is steady or blinking red and whether PON is steady, off or blinking green.
- Result that matters:
- telling total signal loss (steady LOS) from low power (blinking red LOS).
- If LOS is steady:
- start with the fibre cable.
- If LOS blinks red:
- some light arrives; check the cable and report it to Digi if it continues.
- Evidence to keep:
- a photo of the front panel indicators.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Fibre cable at the PON port and the wall socket
- Who:
- you.
- How:
- check the fibre cable is fully inserted at the router's PON optical interface and at the wall socket. Do not look directly into the connector or the optical interface.
- Result that matters:
- whether LOS goes off and PON turns steady after reseating the cable.
- If LOS goes off and PON is steady:
- the router is registered again; check the Internet.
- If LOS stays on:
- the cable does not explain the missing signal; report it to Digi.
- Evidence to keep:
- a photo of both cable ends connected.
Digi's manual warns not to look directly into the optical interface to avoid eye injury.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Turn the router off and on
- Who:
- you.
- How:
- switch the router off with the On/Off switch, wait a few seconds and switch it back on.
- Result that matters:
- whether LOS stays off once startup finishes.
- If LOS stays off:
- the signal has recovered.
- If LOS lights again:
- signal loss persists; report it to Digi.
- Evidence to keep:
- time of the restart and LOS and PON state afterwards.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Report the fault to Digi
- Who:
- you.
- How:
- contact Digi and explain what LOS (steady or blinking red) and PON show, and that the fibre cable is properly connected.
- Result that matters:
- that Digi checks the signal on your line.
- If they find a cut or fault:
- the repair is Digi's responsibility.
- If they suggest a factory reset:
- ask first which settings you will lose.
- Evidence to keep:
- ticket number and date.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Networks
- Brand
- Digi
- Product type
- Fibre routers
Known code variants
- Digi fibra luz roja
- Digi router LOS light red
- LOS encendido router Digi
- LOS rojo intermitente Digi
- luz LOS roja Digi
- ZTE F6705 LOS
What it means
Digi's manual for the ZTE ZXHN F6705 describes LOS as follows: off, no line interruption; steady, loss of signal; blinking red, received optical power is below the optical receiver sensitivity. A PON indicator that is off adds that the router is not registered with the operator's OLT. LOS points to a light problem on the fibre, does not say where it happens and does not prove the router is faulty.
Warnings and stop conditions
- Loweditorial warning
The reset button returns the router to factory values if held for at least 5 seconds; do not use it for LOS without talking to Digi first, because you will lose your settings.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
- Mediumsource verified
Do not open the router casing or look into the fibre connector to see if light comes out: Digi's manual advises against it because of eye risk and electrical safety.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Symptoms and causes
Probable causes · in order
- Fibre cable unplugged or looseCommon
Steady LOS with the cable out or loose at the PON port or wall socket. Confirmed if LOS goes off once it is seated properly.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
- Insufficient optical powerPossible
Blinking red LOS: light arrives but below the receiver sensitivity. It can come from the cable or the network, and only a measurement locates it.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
- Cut or fault on the operator's linePossible
If the cable is properly connected and LOS stays on, the signal loss is beyond what you can check at home and Digi must look at it.
Evidence: Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
Virtual technician
Does LOS still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Manual de usuario ZTE ZXHN F6705 (DIGI Spain)
DIGI Spain Telecom · 2026 · manual
Was this entry useful?