Repairing blown inputs on an Anritsu MS420K VNA (lost beginner)

[cincin]

I have a sweet Anritsu MS420K Network Analyzer that has, I suspect, blown inputs on both channels.
I cannot find a service manual or schematics for this unit, and Anritsu no longer has them either. If you know where I might find them, please let me know.

I popped it open, and I'm trying to get an idea of where the problem might be. The fuses are good, unfortunately, I wish it had been that simple hehe.
Both input modules are the same in the front section, and so far the damage appears to be identical in both circuits.

At the very front, near the input jacks, there's a diode and 4 relays, segregated by a ground plane, that lead to a post connected to a signal wire (top right in the photo). I'm assuming this is the signal leaving the front section. However, the post is shorted to ground. And, the input BNC jack's center pin doesn't have continuity to the diode (top left in the photo), or to the post (top right). So I'm a little confused.

I was suspecting one of the relays may be damaged or stuck to ground, so I disconnected the post from the wire coming out of the front section, but to my increasing confusion the 4 relays and diode are not what's shorted to ground, the wire that connects to the post is. So the short to ground is downstream from there? Yet there's still a problem with something here since the signal doesn't make it through to the post. Or are the relays supposed to be keeping the input jacks disconnected when the unit is off?

This is all based on the assumption that the post in question IS the signal path, and not actually that circuit's ground. I'm assuming that to be the case because the post and wire connection are carefully isolated from that unit's chassis, which it currently has continuity to. But I am a beginner, and I suppose this could be a ground connection, and it is isolated from the chassis at that point so as to maintain a single path to ground. Especially since there's no continuity between the input port center pin and the post, or the input port center pin and ground.

Schematics (or, you know, experience, or actual knowledge) would make all of this so much simpler...

I'm hoping someone here with more experience with VNAs can shed a little light on all of this, or kick me in the right direction.

I'd really love to get that unit going.
Thanks!