I also have a Xuntai telephone exchange 108L, which used to be normal. Recently, China Unicom changed the original two-wire access to optical fiber access. The problem now is that the duty machine will not vibrate when the outside line comes in. It's just that the indicator light of the switch is flashing. Ask Unicom, and Unicom can't help it. Please help me.
My analysis seems to be that the ringing voltage is not enough. I can't even find the manual and circuit diagram on this Xuntai website, and I can't start to improve it.