TIU issues

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I'm curious what version of TIU this is. That said, I believe it could happen to any TIU version.

The cause sort of sounds like brownout- where the voltage regulator for the logic is under too much load (exampled failed/shorted ACT244 outputs) that load down the 5V bus. Again, what would happen, the TIU would power, the regulator heats up, goes into thermal shutdown- you lose all function for a bit, the regulator cools, it works for a bit, shuts off, cycle rinse repeat.

I've seen a TIU in the past that may have had a phasing accident- where all 4 channels took a serious beating and so badly so, all 4 ACT244s were blown (but not the TVS diodes) so bad and failed so shorted that the 5V logic power would not even come up.  That's the worst case scenario. That said, it points to- what if that same beating and abuse only happened on one channel? What if only 1 ACT244 is partially damaged and loading the 5V bus- just enough to push the 5V bus into thermal overload over time.

It might be repairable, might not.

So monitoring the 5v bus during operation should be able to pinpoint that as the problem.

@Dougklink posted:

So monitoring the 5v bus during operation should be able to pinpoint that as the problem.

That's only going to tell you the symptom- ideally you want a thermal camera to check and see if anything is getting hot and exactly what chip(s) are getting hot and drawing excessive power.

Edit- also, I'm not saying for sure this is the error or fault. There could be other faults I've not seen in the wild, other issues, I just don't know. I gave one possible scenario that might line up to the symptom. There could be a situation where it's not overloading power, it's not the ACT244s, it's not the power supply regulator going into thermal shutdown.

anyone have a thermal imaging camera?  I will volunteer the test subject. 

Truthfully, I usually check the ACT244's with a small inexpensive IR contact temperature sensor.  Here's a typical one from Amazon, Mini Infrared Thermometer.  If the ACT244 is drawing excessive current, it'll be warmer than the others.  Note that this is with nothing connected to the outputs of the TIU.

I have one of those - will report back my findings

they are just a tiny bit above ambient - assume this is good?

Hi isn't it more common for the ACT244 to fail then the voltage regulator going bad!

Alan

The problem is he states he has outputs and it can run trains for a period then fails.   So what is shorted that allows it to run then drive VR down.  Or is there some other processor component that just is sporadic once powered up.

My experience is shorted transmit or receive chips that can drag down voltage don't transmit and function. And drag other channels down too. 

If you're dragging down VR you don't need a sensor, just touch the VR heat sink.  You will know if it is HOT!  Try replacing it.

But it could be a 3.3V regulator killing the 5V and that means a processor chip failure that can't be repaired.  Again sporadic though.  I have not seen that before.  Unless you're not accurate with your description.  G