Thanks for your reply. Did already watch the four parts video some time ago. The first one shows a PSU failure when connected to mains, but the DC-DC converter part still works. And the EEVblog kangaroo didn't repair his PSU, or at least video #5 was never released.
Mine has complete failure (both mains and DC powered).
However Mark Bielman in the HP-Agilent-Keysight-equipment groups.io list provided me with a schematic of a less powerful version of my NFS177, which I reproduce herewith. Thanks to him.