I've got an old Equity III 308 (circa 1987) that has been working fine for the past twenty some odd years. Now, when the KSU is powered up, it honks like usual, and then the led on the front goes out and the phones don't work. When I turn it off and unplug it, the stations that are connected squeal for three seconds or so after a few minutes.

Does anyboy have any ideas as to how I can fix this?