Flashing Cab Light and loss of Legacy Cab2 Motor control

No, not a faulty board. "the cab lights blink on and off." Indicating a stalled motor detection has kicked in.

That is exactly how it is supposed to work to protect you and the motor. If it cannot read the tachometer of the motor spinning (or the motor cannot achieve the commanded speed step RPM) then it assumes the motor is jammed and cannot spin. Rather than the motor control circuit ramping up the voltage (PWM) to the motor trying to achieve the commanded RPM but cannot and thus possibly burning out the motor, it stops and blinks the cab light, and then locks out any further motor drive until reset.

" If I power down and restart, all is well."

Correct again- normal and expected. That is how you reset the locked motor state. You can also hit 0 on a CAB1 or CAB2  reset button to reset via TMCC/Legacy. Power cycling track power completely (full off and then on) either in conventional or even in command also resets.

Note: you can cause this fault to be tripped if the track voltage is lower (example less than 18V) than the current speed you are commanding requires and the motor cannot achieve that speed- again, the controller assumes this is too much load and could burn out the motor so it locks out motor drive until you power cycle.

I tried pulling the manual for your engine (SW8 series) from Lionel support but got document not found.

That's OK because I know for a fact your engine uses the same board set- LCP2 and thus the manual from my SD70MAC is valid as far as this error and cab blinks and motor drive.

https://www.lionelsupport.com/...d-NonPwd%20Units.pdf

Page 44

Obviously, do the common sense check and ensure the gears are not jamming (ballast or something else binding the driveline).

However, since you said it did reset and run correctly with a power cycle- again, sounds normal- you just somehow invoked this stalled motor safety. That's just how the firmware works to attempt to protect the motor and drive circuit.

You may not have been aware of this feature and it might be more sensitive to voltage or track current problems in certain conditions that kick the safety in.

I have had the RCMC do this exact thing, and a couple of them were indeed a bad RCMC board.  I agree in most cases it really is a stalled motor, but not always.

I had this problem with the new Acela.  Before returning for repair:

1) Change transformer/power source. Strangely, replacing my ZW with the Lionel PH180 or MTH Z1000 solved the problem.

2) Ensure minimal resistance between power source and track. Temporarily add wires between power and track.

3) Reset Procedures – If the engines fail to respond to commands (e.g., cab light blinking because its software “thinks” there is a motor binding issue), try to reset the engines. Here are two reset options:

          Reset option #1 when continuous one-blink error code occurs: (Idea thanks to @MineRun) This “unbinds” the motors to the satisfaction of the engine software

• Hit reset (“R” with octagon around it) to turn off the blinking cab light,
• Press down the 'boost/brake' wheel to reverse the direction,
• Turn the speed wheel clockwise to back the engine up ever so slightly
• Reverse direction again
• Turn speed wheel again to move forward

          Reset option #2 for general reset:

• With power on track, press the “R” with the octagon around it. The engine should respond with a short whistle.
• Turn off power to track
• Turn off command base power to stop TMCC/Legacy radio frequency from reaching the track
• Wait about 30 seconds.
• Restore command base power
• Restore track power.
• Turn speed wheel to move forward

I have the NYC version of this locomotive. I learned that it is sensitive to low track voltage and couple that with more than 4-5 cars it will stall and throw a code.

My solution - added another power drop to the back-end of my layout (I have a small 5x9 with one Powerhouse 180 and lock-on) and I only run it with 2-3 cars. These are geared pretty low and are not designed to handle more than 3-4 cars for an extended length of time.