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.

 

[pucho812]

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.

Yes. I have new connectors coming as the metal tabs broke off a few of these.

 

[JohnRoberts]

are they using PC edge connectors?

Look at the PCB layout are there any common pins/fingers...?

JR

 

[Brian Roth]

are they using PC edge connectors?

Look at the PCB layout are there any common pins/fingers...?

JR

Belated reply. On the rear of vintage/reissue Neve modules they used a FEMALE edge connector with fork contacts. On the original desks, they used a MALE edge connector down inside the frame. Amphenol (and others?) sold the combo as the 133 and 143 series. I always thought it was odd having male blades sticking up "in the breeze". Also, the metal pins at each end of the male blades were very weak and would bend or break off. It looks like the AMS reissue module frames have a small, conventional PCB with gold plated "fingers" down inside the frame for each module position.

https://www.ams-neve.com/wp-content/uploads/2021/10/1081_Rear.jpg

 

[kags]

In my modules, the little support tabs that set the height of vertical modules in a rack get bent, causing misalignment of the edge connector - see image. The image show circle around the “upper” tabs when racked, and the same tabs are on the bottom edge

 

[Brian Roth]

OK, I remember those "tabs". Years ago, a friend/client had an 8068 desk and I had various modules in and out during the many years he owned it. But, all the sheet metal seemed quite sturdy and I don't recall any problems with those guidance tabs. I actually thought they were a clever design element.

Maybe we were just lucky...

Bri

 

[kags]

The ones on these early 2000s modules are soft as butter. A weak point, for sure