We have 7200 VXR NPG1 router, in which two STM links is been terminated,

all of a sudden, STM links went down,

when coordinated with provider, they have initiated a bi-directional loop, in which we were not able to see the loop at our end for both the STM links,

even when loopback cable is connected, we were not able to see the loop.

we tried changing the fiber patch card,

card was made shut and again no shut was given.

tried with a new pos card.

even rebooted the router.

still serial was up and line protocol was down.

while checking the logs, we found %sonet-4-alarm been generated.

finally card was terminated in the same router, but in a different slot, then the link has come up.

Is there any chance for the power level being increased in the fiber card in working condition, which may damage the controller.

what could be the reason in this case.