Arcing in Kato passenger cars

[OldEastRR]

While trying to clear up the flickering lights in some Kato coaches my first step is to clean all the gunk off the wheels. While doing so I noticed a few places where the black spots didn't just wipe off. In fact I had to scrape them and doing so revealed small pits under the spot. Like arcing.

Polished them up real nice, ran the cars -- still flickering. So I decided to break down the car entirely and look at the entire circuit. Besides the usual dull corrosion on the long contact strips, the connectors to the lamp, and the tops of the truck tabs I saw more signs of electrical burns  on the long contact strips.  And not near where the truck tabs touched them.

This is really weird. I know you can get arcing in N locos. I've heard of a lot of quirks in N scale stuff but never this before.

These two Kato coaches are most likely from the original sets Kato released in the '90s, and have had first bulbs and then upgraded to LEDs when they came out. They've run on both first DC and changed to DCC (since 2014) for probably hours and hours.

BTW, all the rest of the cars with these come from sets made in the past 12 years or less and run fine.

[peteski]

Arcing will  occur when 2 metal contacts are separated while current flows between them. No current  - no arcing.  The more current flows, the more intense the arc will be. So incandescent lights consume more current than LEDs, so the pitting could be more severe. But if the discolored/pitted  areas are not at the contact point, the discoloration was caused by something else. Guaranteed. Arc is basically plasma: superheated gas (the ambient air) which is created by electric current flowing through the gap between conductors).  The point of contact of metal with the plasma can become pitted.

In my experience with Kato car lighting, 99% of the flicker is due to the intermittent connect between the rail and wheel tread, and possibly at the contact area of the axle point to the bearing cup. Cleaning rails, wheel treads, and the axle points/cups cures most flicker issues.

The points of contact between the truck's protracting contact and the flat metal strip can also cause  flicker (which is intermittent  contact), but to a lesser degree.  Yes, those also need to be clean.  I actually polish those points of contact.

[OldEastRR]

And the last place to think of for flicker is the LED  assembly itself.  As it turns out, that was the problem. Apparently there is a bad solder joint (which I still must fix). I replaced the original LED w/ another and it works fine. This happened in one of a friend's Kato light sets so I guess it can happen again, tho very remote.

[peteski]

And the last place to think of for flicker is the LED  assembly itself.  As it turns out, that was the problem. Apparently there is a bad solder joint (which I still must fix). I replaced the original LED w/ another and it works fine. This happened in one of a friend's Kato light sets so I guess it can happen again, tho very remote.

Yes, that is not something one expects.  It is a rare occurrence.  Sounds like you took care of the problem.  But your original post implies that several coaches has this exact problem, or did the flicker clear up after cleaning of all but one car?

[OldEastRR]

Cleaning fixed the other car.

[mmagliaro]

If the problem was a bad solder joint to an LED, why did you have to replace the LED?  Could you not have just resoldered the joint?

[nkalanaga]

Maybe he means the "LED assembly" and just shortened it to "LED"?  That would make sense, faster than resoldering, and if it worked, he could resolder the original at the workbench.

[OldEastRR]

I only assume a bad solder joint since it seems likely. I'd have to partially disassemble the LED unit to get at the circuit board leading from the inputs to the chip then to the LED. Just replacing the light was faster  -- I'll get around to checking the solder someday, along with the thousand other "I need to fix this" projects I have.