Had my first PS-3 locked in forward. It would start moving about 2 seconds after power applied while dark and silent. Could not unlock as it was moving in conventional and also wasn't sure if there was a board failure. After checking board was good, and finding that it operated fine in DCS, I went back to conventional ops.
With the voltage down around 7VAC and the train barely moving the engine finally started up after the super cap charged. Once it was started and making sounds I was able to do a Conventional reset of 1W and 5B. Got the confirming 2 toots and when I hit the direction button it stopped. Cycled properly in conventional.
I think the trick with this is the board must start up, so you need to keep voltage low enough that the train doesn't run away, but enough to get it started up and then do the reset, or the unlock procedure. G