TMCC K Line SD75 Disable Ditch Light Flashing

I'm literally working on this exact engine at the moment for another hobby shop.

I would advise against that- but hey, that's me.

Why? Well, it's the motor driver. So I would not mess around with bonding 2 alternating outputs even if they are the same voltage given that the recent lack of DCDS motor drivers for replacements, and the fact this is actually K-line making it rarer. Again what we know is, this is a board you really cannot afford to damage

If you want constant on LEDs, then wire them up to a regulated current controlled source besides the motor driver.

Again, the problem is, I think the outputs are possibly driven directly from the micro controller-same one that does the cruise and motor control in general. They might be buffered with a transistor, but again, they also could be direct output pins. A lot of times those can be 3 state pins- grounded, floating, or hot. If they were coded (and we do not know the firmware) such that they toggled grounded and then hot- shorting 2 of them together is very bad.

Now it also may be there are current limiting resistors in series to those pins, but again, I'm not going to test on a customers engine, I'm not pulling the shell off again, and like I said, sure, on paper you just saw a 3V blinking//alternating LED pair where one is always on so shorting together means both are always on. Conversely, the "how" they blink off and on for a given output goes from "no big deal" to "oh poop" the first time you blow the horn.

Picture I found of the backside of that board and I zoomed way in but could not identify the exact components or values, just the general location and size near the output pins we are discussing. Point being, what I saw was no buffering and thus direct out of the PIC with at best a resistor in series. IMO, not worth risking- over a simple LED set that could be powered other ways.

Wow thank you so much for the detailed reply!  You’ve convinced me - definitely won’t be doing that.  I’ll find another option for wiring them.

I don’t have a lot of experience with these K Line cruise engines.  Is it normal to have some stuttering/flickering lights when moving at very low speeds?  It seems to do that then smooth out as it gets above speed step 5 or so.  It’s more pronounced when pulling a load.

Thinking about upgrading to ERR Cruise Commander M at some point anyway, though.

On another note, these K-Line SD70/75s are some of the most underrated models detailing wise.  What a masterpiece.

@Catonsville Central Railway posted:

Wow thank you so much for the detailed reply!  You’ve convinced me - definitely won’t be doing that.  I’ll find another option for wiring them.

I don’t have a lot of experience with these K Line cruise engines.  Is it normal to have some stuttering/flickering lights when moving at very low speeds?  It seems to do that then smooth out as it gets above speed step 5 or so.  It’s more pronounced when pulling a load.

Thinking about upgrading to ERR Cruise Commander M at some point anyway, though.

The why for LED flicker is easy. Remember, this is still relatively early TMCC driven by the R2LC C08. That uses TRIACs for the outputs originally meant for incandescent bulbs. LEDs being diodes, are DC devices, and even then, the TRIAC on the R2LC needed more "load" so often small capacitors are added to more reliably trigger the TRIAC and given DC, every other swing of the cycle. Again, you have a circuit designed for AC and an incandescent bulb- adapted minimally for making an LED light. It works, just not "bulletproof" and "flicker free".

So then you have motor controller based on RPM feedback pulsing relatively high current draw for short periods while trying to maintain speed control. This load affects the AC and thus can affect the TRIAC firing for the LED that already on margin of error, already flickering anyway 1/2 of the AC power anyway. Interruptions of that then become visible.

Modern Legacy and other engines convert to DC, bulk filter with capacitors, and then use transistors (typically FETs) along with voltage regulators and more capacitors. Thus LED lighting is mostly flicker free even with current draw of the motors and other functions.

The ditch lights are indeed driven from the DCDS, and shorting them together is not a really good idea.

If you really want them to be on constantly, just wire them to track power with a resistor and diode, job done.