Have an issue with a DSX-40.
Doorbox works fine everytime I test.
However, everynow and then, the doorbox circuit remains engage, even if the doorbox is disconnected from the system.

I programmed a DSS for the dorbox extension and when it is in this state it is flashing slowly as though it is on hold.

Unable to pick it up any where.

Any thoughts? I normally do not work on the DSX systems and I know they are very quirky when you are not used to them.