[JFreak]

It is not so hard to troubleshoot as you have already found one block of 8 inputs is not functioning.

What you need to do first is disconnect any other interfaces but leave one of those you "know" is working properly on all inputs. Only that single interface connected to core card. Then swap that "faulty" input card to the "working" chassis and see if that card can or cannot get signal. If it can, it is working. If it cannot, you found your culprit.

Now if it somehow can pass the signal, do the opposite. Insert the previously working input card to the chassis that was malfunctioning and again only connect that one interface to core card. If the previously working card is not working in the previously malfunctioning chassis you have proved that chassis has a problem.

Those are old boxes. Some of the problems may go away when you clean the internal connectors with industrial alcohol. If not, replacement 2nd hand boxes are not so expensive anymore.