NI VXI-8360T CB-TRIP LED coming up red on bootup.

[WyattJ]

I have a VXI chassis with a MXI2-Express controller card (VXI-8360T) and sometimes, with a certain card installed, it will sometimes fail power-up with the "CB-TRIP" LED turning red right away.  It seems to happen in streaks.  If it passes, it will usually pass many times and show no issues.  If it fails, it will continue to fail.  The only thing that seems to restore it is leaving it alone for quite a while, but not always.  What exactly is this failure?  The User's Manual is very vague.  Why would there be a circuit breaker on this card for the 5v line?  How does it even know how much current other cards are drawing from the mainframe?  What are the conditions that would cause it to fail and can these be modified at all?

[Air_Frantz]

Hello,

The circuit breaker in the module is for protection in the event that there is an internal short in the controller.  It should flip when the module draws more current than expected in operation.  If the other card is pulling too much current from the 5V power line, that could cause the voltage to drop on the line and the 8360T to draw more current to compensate?  Have you tried probing the 5V rail of the chassis during this power up event?  This could show if the chassis power supply is keeping up with demand on boot.

[WyattJ]

Hello Jon,

We did probe the 5v rail.  It's slower to come up than in some other chassis, but I don't see a significant difference between when it passes and when it does not.  Can we get more information on what exactly causes it to trip-- that is, what voltage or current levels and what timing is critical (if there is anything)?  When we slow down the 5v ramp even more, it fails consistently.  I don't know why a slower ramp up could cause a circuit breaker to tip-- usually that happens if there is too much current.  If current is too low, it doesn't seem like that would actually present a potential problem for the card-- that is, risking component damage.  Is there a jumper or something we can modify to change this behavior?

I wanted to send a photo of the scope capture, but it won't let me attache the TIF file even if I rename it :(.

[Minions]

There is generally a specific power-up order for devices - especially ones that have a core at a lower voltage and the I/O powered by another higher source.  Scope the rise of all voltages for your chassis to see if it might be back-feeding and therefore draw too much current on a supply.

[Air_Frantz]

How are you slowing down the 5V ramp for that test?

At this point, I think you should open a Service Request(if you haven't already) so that we can take a deeper dive into troubleshooting the behavior you're seeing.  That way, we can possibly get some insight from our R&D group on the specifics of the CB circuit.