Old thread but I found it looking for a solution for one ISS.7 I have. It was lock at the Minerva Logo and it couldn't start TK2 so I suspected a problem reading extra ROMs or high adresses.
After a lot of tests I decided read the Service Manual and it says that TR8 is needed to place Active Low DSMCL and this is needed to start expansions, so I changed the old MPS2369 transistor with a chinese ZTX313 and... voilá, this ISS.7 is working.
So another thing to check if someone has this problem.