I thought I would share what I did this week to eliminate flickering in the AM Amtrak set I picked up last year at a bargain price. The set seems to have had very little run time, so it's in great shape, but every one of the 4 cars flickered constantly. I couldn't figure out the cause after trying the easy fixes....cleaning wheels, ensuring pick up wires were making contact, etc. So I decided to try replacing the light board with the lighting regulators from Hennings which include a capacitor...
and an LED light strip...
Unfortunately, it still flickered! So I turned my focus to the trucks, wheels and pickup wires again. Then I cracked the problem.
On these cars the current passes from the pickup wires through the truck screws.
However, the pickup wires are loosely coiled around the screws, so the screws need to be in pretty tight to make contact consistently. But when you screw it in tight enough to compress the pickup wire coil and thus achieve constant contact, this presses the top of the truck against the flat bolster
Therefore, the truck becomes rigid and loses the ability to "wobble." As a result its wheels cannot stay in contact when starting up a grade or going through curves.
My solution: Don't use the screw to carry current. This allows you to back the truck screw out which gives the truck enough degrees of freedom for the wheels to stay in contact with the rails. For power to the light regulator, I drilled holes in the floor and through the truck so I could feed a superflex wire through both holes and solder it to the pickup wires.
The result....no flicker at all. Hooray.