one workshop has been running single mode fiber cable with 2 multimode for several years that we didn't find out. i had monitored the switch before, only fond the transmission has too many error bits but don't know why. the fiber connection is working.

finally several days ago the fiber no longer work. so i had a complete check on it. it was strange that this is a single mode fiber while the attached convector is a multimode one, and it had been working for several years. this cable was paved by China Telecom engineers. its the only single mode fiber exist between workshops, all other fiber are multimode. it seems the China Telecom engineers made me a joke.

i had tested the fiber with red light, it seems no problem, i can saw the light from another end. also tested the converter by replace it to other existing converter, works fine too.

anyway i bought 2 new single mode TX-FX 1000M converters to replace the multimode converters, now the fiber works again.