There is a bad batch of fuse holders on several of the data East boards PPB and Power Supply boards some of the same style are not effected.
This board has had already this fuse holder repaired with solder.
Suggest replacing all the fuse holders, checking the power supply fuse holders also and rest of the PPB board. All it takes is the same pressure needed to remove a fuse and the bad batch ones break, these faulty holders no longer have spring load to keep a fuse secured and cause resistance shorts
Boards can be sent out to have this service performed.