Cannot access service menu on C7280i / service menu locked?

Hi Guys,

I own multiple C7260i printers (among many others Canon imagerunners) and recently got one used C7280i. This is probably not important, but all of those printers run with Fiery A2 or GX 400.

So, we can access service menu on all our printer from the C7000/C9000/C7200 series using the * 2 8 * key combination, - but on this one particular C7280i nothing happens! no service menu, no error message. Just nothing. What can it be? Was it possible to lock the service menu access on those machines?
Maybe you can help me. I hope!

P.S. I found an information in the C7200/C9200 Series service guide about a Canon "NAVI" software which one can use to connect to those machines from a laptop (and possibly access the service menu), but I was unable to find any more information, also found no way to download this from anywhere.