Strange aiu switch problem

No fuse/breaker inside the AIU.  

Can you "hear" an AIU internal relay click when you throw a SW port after the first time?  Can you hear an AIU internal relay click for an ACC port when you press ON/OFF or ACT?

I realize swapping a working AIU would be a pain if you have all 10 switches wired in.  So perhaps you could swap in a different TIU in the albeit unlikely event it's the TIU that's the problem.  Ought to be easier (fewer wires/cables) to change out the TIU to the suspect AIU.  This would isolate the issue. 

There have been reported cases of a digital IC chip going bad in the AIU.  While the components within the AIU are generic and relatively inexpensive ($1 or so), diagnosing and replacing chips is not in everyone's comfort zone.

I do here the click the first time. I also tried a different AIU with the same result. Going to switch the TIU next.

Steve,

Before swapping the TIU, I'd swap the cable between the AIU and the TIU.

Tried the cable, same problem. Swapped out the TIU and everything works.  The rest of the bad TIU works fine. It's just what ever powers the AIU that isn't working.

So if you take that "bad" TIU and attach it to a known "good" AIU, does it work?

Nope

Ouch! 

Sounds like TIU circuitry that talks to AIU is flakey - you confirmed TIU-to-AIU cable is in order.

Even in the TIU, the components involved are inexpensive but I can imagine labor and 2-way shipping costs might be more than the cost of a new TIU.  Your local repair guy (if you have one) should ask if the TIU is/was powered via Fixed 1 or via the AUX PWR In jack.  

Curious as to how you proceed.

Look inside the AIU port on the TIU for bent or touching pins.

Don't see any  bent or touching pins.

Are you inclined to attempt component-level troubleshooting/repair or just take it in?

Since you have 4 TIUs and 4 AIUs, does your layout/wiring allow you to run two AIUs from one TIU?  The AIU-to-AIU cables are less than $5 for a 25-footer.  Apparently, the one "bad" TIU works perfectly except for ability to talk to an AIU.

I had a spare TIU so everything is working fine now.  The AIU's  are spread around the layout so the 25' cable probably will not reach the next closest one. 

Corsair, I also have had a TIU, Rev L, that had AIU issues.  After having it run switches fine, when I went to add some accessories, I found it would not properly work the AIU's accessory relays.  I would up replacing the TIU.  I decided against having the TIU repaired, because I've had several issues with it over the years.