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Here's an odd one that came into my shop recently.  The product was a recent Lionel Legacy Station Sounds Diner.  The issue was that it couldn't receive TMCC/Legacy commands if the lights were on!  It was tried on multiple layouts and failed on all of them, but turn off the lights and no sweat, worked perfectly.  OK, that's an odd one.  Apparently, it had been back to Lionel multiple times and they didn't find anything wrong.

First test, I put it on my bench and fired it up, worked fine.  Turned the lights on and it still worked fine.  OK, let's move over to the layout.  Same results!  I'm starting to think the customer has a vivid imagination.  After some discussion, I decided to crack it open.

The lighting is totally separate from any of the other electronics, it simply gets track power through a lighting control switch.

I wondered why the lighting could affect the TMCC/Legacy signal, and after examining the lighting board briefly, I have my answer.  As I suspected, Lionel went for massive overkill on the design of the lighting for something that lights a measly four LED's!  This is a switching power supply, unfortunately sometimes known for being electrical noise generators.



Note the arrow above pointing to an inductor, below is what I see with my 'scope at that point.  That's a 20V amplitude signal coming from that  coil, that's certainly some electrical noise being generated!  The signal was 15khz, and I'm sure the harmonics go far beyond that, maybe right up to 455khz?



When I looked on the other side of the lighting strip I found this.  The arrow again points to where the coil is located on the other side.  In case you don't recognize that brass strip, that's the antenna for the TMCC/Legacy signal!  It's sitting right on top of that source of electrical noise.  It's hard for me to believe there's any other cause of the issue than simply injecting big bursts of noise into the TMCC/Legacy antenna signal.

The ill-advised positioning of the antenna is a total mystery to me!  I suspect the lighting strip might not have been an issue if the antenna was far away from the switching P/S.  However, since it didn't fail for me here, I didn't feel like doing a repair that I couldn't verify and finding out that it didn't address the problem.  Since I was pretty sure of the reason for the issue, I also was pretty sure that simply eliminating the switching P/S would fix the issue.

I don't understand why it only affects specific layouts, that's a research project for another day.

Since it seemed clear that it would be a PITA to hack the lighting board to fix it, I simply removed the lighting board and installed my LED lighting regulator and a strip of LED's.  Better lighting anyway than four measly LED's.  To minimize the impact, the same connector was used on my LED regulator board and I plugged in the existing wiring harness that supplied the old lighting with track power.  Unless you crack it open, you'd probably never know it was modified, documented operation remains the same.

It's a little difficult for me to believe that other folks haven't had similar issues with these cars given this one failed on multiple layouts.  In case you're wondering, yes it now works fine on the customer's layout.

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Wow, that's just one of those crazy things you don't know you could be sitting on John. I wonder if some operators have had it where it has stopped working only briefly and then gone right back on. I'm guessing this is really hit or miss to discover, wonder if Lionel got a few and had nothing show up on the radar. I seem to remember Dave talking about something(maybe the Mogul or some other engine) that he couldn't replicate the issue that was described on the topic. If I recall, it was both frustrating for Dave and the poster on that problem.

Wow, that's just one of those crazy things you don't know you could be sitting on John. I wonder if some operators have had it where it has stopped working only briefly and then gone right back on. I'm guessing this is really hit or miss to discover, wonder if Lionel got a few and had nothing show up on the radar. I seem to remember Dave talking about something(maybe the Mogul or some other engine) that he couldn't replicate the issue that was described on the topic. If I recall, it was both frustrating for Dave and the poster on that problem.

I'm wondering the same thing. There also might be some of these sitting in a box that people haven't tested yet, but I suspect they should dig them out and try them.   It's hard to truly blame Lionel service, since it worked perfectly on my layout, I suspect they had the same experience.  I blame the person who decided it was a good idea to stick the TMCC antenna next to an EMI generating power supply.

@zhubl posted:

That is a crazy find. Just out of curiosity how new was this diner? I am pretty sure my up excursion diner doesn’t have a switching power supply and I definitely not remember the antenna being on the other side of light PCB.

This was a pretty new diner, Lionel 2127090.  As for the switching supply, if you have the LED lighting that has the supercap that holds it up for a minute or so without power, you probably also have the switching power supply.

I'm wondering the same thing. There also might be some of these sitting in a box that people haven't tested yet, but I suspect they should dig them out and try them.   It's hard to truly blame Lionel service, since it worked perfectly on my layout, I suspect they had the same experience.  I blame the person who decided it was a good idea to stick the TMCC antenna next to an EMI generating power supply.

This was a pretty new diner, Lionel 2127090.  As for the switching supply, if you have the LED lighting that has the supercap that holds it up for a minute or so without power, you probably also have the switching power supply.

Ah, from the Cardinal train. Figure that the design change could be in both directions, back a year or two and ahead for anything that is still yet to come. Maybe Dave should have a look at it, that is this topic or direct email?

@zhubl posted:

Well I don’t know why I had this picture but this is the lighting strip in the original 21” cars. I know it’s not a very good shot it’s old and like I said I don’t know why I have it. Put looks like it’s a standard 5V linear voltage regulator L7805CV

That is a linear regulator based supply and is basically what my little module does.  My module also offers DCS compatibility and intensity adjustment capability.  The only thing I left off is the supercap, I never did understand the need to keep the lights on for extended periods with no power, I just want flicker-free lighting while I'm running.



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