SCXI 1001 - No modules detected

[struct_tests]

We have a four-chassis SCXI system that recently began reporting errors detecting the installed modules.  After receiving an error -200073, I've been troubleshooting the setup using NI-MAX. Two of our chassis seem to be working fine if I connect them individually or together. If I connect either of our other two chassis to the chain, then no modules are detected on any chassis; it acts very similarly to if one chassis doesn't have the power turned on.

I think there might be some kind of power problem, but I'm at a loss for how to confirm the issue or if I can do anything to fix it!  Can anyone offer advice on how I can proceed?

Some troubleshooting/info:

• The front indicator lights are dark on the two "bad" chassis. (One of the good chassis also has had a burnt-out light for a while)
• All four units seem to have power and the rear fans run when power is on (even if the lights are out).
• All three fuses seem fine on all chassis (checked with a multimeter and by swapping between good/bad chassis)
• The problem seems to be coming from the chassis and not an individual module. I removed all but one of the modules from a bad chassis and the detection issues remained.  I repeated the check with three different modules (all SCXI-1520), one of which I also verified was detected on a good chassis.  I also swapped one of the modules (SCXI-1520 again) from a good chassis.
• I tried connecting our "backup" WinXP machine (older software, but was it worked with the hardware) and received the same detection problems.

System info:

• 32-bit Win7, NI-MAX version 14.0.0f0
• The four SCXI-1001 chassis are connected to the PC via a PCI-6281 card
• All modules are either SCXI-1102 or SCXI-1520
  • The two "bad" chassis each had twelve of the -1520 modules
  • One "good" chassis had six -1102 and six -1520
  • The other "good" chassis had six -1520 and six empty slots