Todays puzzler chassis slots and units

[pucho812]

So I have 2 modules. They are the same module but for sake of discussion we will call them 81A and 81B. They fit into a 1081 8 unit vertical rack ams and are reissue units.
If I take module A or B and place them into slot 8 of the chassis they both work perfectly. If I place them into slot 5, one works and one does not. basically A&B work in slot 8 but only A works in slot 5.

As we know slot 8 powers both modules without issue, we can assume the slot is ok and we can assume that because both modules work in slot 8 that they are ok. In fact testing them with the AP yields expected results.
Both modules appear to measure the same physically including distance from the edge connectors.
In fact any measurement with a ruler comes out the same.
But slot 5, one module is working one is not.
The short answer is use the modules in the slots they are working in. No real harm or foul there.
But I am stumped as to why both modules will work in one slot without issue but only have one of the two working in another slot.

 

[Brian Roth]

Can you "peek" into the rack with a flashlight (and no other modules installed) to see what is going on at the back side? I once had a similar problem with modules in a (second owner) MCI JH-636 desk. Turns out the frame had apparently been slightly "distorted" during shipping and the modules weren't always seating into the edge connectors on the left side of the desk. I had to add shims below the motherboard at that end to get everything lined up.

Bri

 

[pucho812]

Can you "peek" into the rack with a flashlight (and no other modules installed) to see what is going on at the back side? I once had a similar problem with modules in a (second owner) MCI JH-636 desk. Turns out the frame had apparently been slightly "distorted" during shipping and the modules weren't always seating into the edge connectors on the left side of the desk. I had to add shims below the motherboard at that end to get everything lined up.

Bri

That’s my thought too. Nice to get a professionals second opinion. That the most likely culprit is that they are not making proper contact in the one slot but are ok in the other slot.

 

[kags]

I have an AMS rack that is very finicky about the height of the 1081 edge connectors. The modules have a metal tab that protrudes from the side of the module, aligning their height with the rear mating connector. When a module is pulled, sometimes the tab gets slightly bent towards the frame and then the module won’t power correctly. I initially thought it needed shims until I noticed the metal tabs were bent. Really soft metal for a critical part.