Quote from: DCC Sodor on January 11, 2026, 08:24:57 PMI am curious if there are resistors on board the PCB for LEDs or if that is something that would also need added.

It's a little hard to make out in the photos when they are compressed to fit in the forum's minimum size, but for both the H and B pads, there is a single SMD device wired between the pad and the corresponding pin on the large IC. Given that they are pads to drive LEDs, I would assume they are resistors. If I have reason to open it up again, I'll try to measure the resistance. I will say that the manual for the large-scale board says to wire a 1.2 kΩ resistor in series with the LEDs. Not sure why the HO board would be different, but maybe they figured that any future product that included lights would be more space-constrained. Adding two SMD resistors probably costs 1-2 cents per board?

I recently got the HO DCC Thomas and Percy locomotives, and to see how they worked and what we might expect in the future, I disassembled Thomas. From what I can tell comparing the locomotive to the exploded parts diagram of the non-DCC sound and moving eyes Thomas, it looks like they are probably identical, apart from the PCB board. The PCB is mounted under the cab roof, and the speaker is at the rear, with the rear of the shell forming part of the speaker chamber.

The PCB has part number AE32129. It seems to be a shrunken version of the large-scale Thomas DCC board sold by Bachmann. The manufacturer CVs are identical to the large-scale board (CV8 = 141 (SoundTraxx, CV7 = 86). It seems to be loaded with the same character sound options (Thomas, Percy, Edward, James, Henry, Gordon, Toby, Spencer, Emily), settable by CV 115.

Like the large-scale board, there are four unused solder pads on the PCB, two labeled ground and two labeled "H" and "B," presumably for headlight and backlight. That said, the locomotive is extremely tight inside, between the motor, eye unit, speaker and chamber, and the weights, so trying to retrofit with lamps would probably require shell modification just to route wires and/or light guides (along with holes and mounting for the LEDs).

A couple of my disassembly photos are attached.