Case
of DH165IPs. Installed to Atlas Trainman+ GENSETs plugged into 8 pin port. Ditchlights installed front and rear. Original LEDs headlights remain in place, with high efficency 1.8mm used for ditchlights replacing the original Atlas SMD LEDs on a circuit board tied to the headlights.
Annoyingly PHL30 works great but PHL31 has the flickering when lamps should be off. Substituted LEDs and problem remains. Swapping decoders and problem follows decoder. Digitrax replaced decoder but the issue remains. Programmed decoder after full reset with no change in results. The high efficency LEDs may be the problem but they fit the bill for illumination and substitutes that will physically fit the space are not on my radar.
I'm slowly going mad over this, and other projects keep backing up as I continue to waste time on flickering lamps. I was hoping for a 'magic bullet' to solve the flickering once and for all, and let me move on to other projects...
This does seem to be a really strange problem. I'm not familiar with the way modern H0 locos are constructed so I don't know if my advice will be valid or not.
You say that the problem follow the decoder (even the new decoder you got from Digitrax)?! So you can put the "bad" decoder in the PHL30 and it's ditch lights will start flickering? And by the other token, you can take the "good" decoder and put it in the PH31 and the PH31 LEDs will not flicker anymore? You're right - that doesn't make sense.
Is it possible that the "good" decoder is a different revision than the "bad" decoders (maybe the actual layout or the components is different or the components in the decoder are slightly different between them)? The other thing (even though if the fact that the problem follows the decoder makes this irrelevant) is a question whether the LED circuitry (outside of the decoder) in the PHL30 and PHL31 is identical? Do they both use the same LED circuit board?
As far as "high efficiency" and "normal" white LEDs, all white LEDs are all pretty efficient and will emit light even with a fraction of milliamp going through them. What makes you state that the 1.8mm LEDs you are using are more efficient? Do you have any specs for the original Atlas LEDs and the 1.8mm LEDs which show the difference? I'm not trying to doubt you or trap you - just asking the questions I would ask if I was troubleshooting this myself.