For the DCDR to be faulty in go full tilt, more then likely a shorted triac. But since he says he can occasionally get it to go in reverse with MTH system, that does not make sense. This may very well be the 50hz also causing lack of good communication to the RS board. By the way the RS board is the K-Line version, or OEM version Lionel sold, so the chip is soldered on. I would unseat all boards and reseat as a simple solution. Then try it on conventional with 60hz ac source. If all functions work, you found your problem. Then again, if you have other TMCC engines working on your layout, all except this one, I doubt it is the 50hz.
At that point swap in a different R2LC. This also looks like it is the older Mother Board with Jumpers for Conventional or TMCC configuration. Might be a jumper in the wrong spot. The Tender should work all by itself in conventional. For TMCC function it would need to be connected to engine to get Serial data.
When power applied does tender stay quiet unit you press startup; or does it start making idle sounds as soon as power is applied? G
