I'm really not sure what you're referring to when you say the bulb is soldered in. The bulb should be a grain-of-wheat with attached leads that connects to the motherboard in the loco. It'll typically be held in place in the strobe dome by either the window shell of the cab and/or a self-adhesive heat reflector. There shouldn't be any solder anywhere near any of above.
But before we go further, first be certain that you didn't turn the strobe off accidentally. The AUX1-9 command with your TMCC CAB-1 should turn it back on if it was previously toggled off.
If that doesn't fix the issue, some photos would help to show what you're seeing inside the cab.
TRW