When putting a butt set on it to monitor all I get is a click when the ring should be present, don't hear the 20hz. You'd think if had anything on the back plane causing it, it would also affect the two built in slt ports. I could find nothing that looked like a fuse on the back plane or the card, but it could be a cap, but I don't see any that look swelled or blown. Of course without a SD I'm flying blind as to how the circuit works.

Retired phone dude