strange engine startup issue

The engine has had the battery removed and a bcr circuit installed.

Replace the BCR with a fresh, fully charged 8.4 NiMH battery and se if problems still persist.

Also, do a DCS signal test with the engine stationary, right where it is when  it starts up by itself in conventional mode.

Okay - so you think it is starting up in conventional mode, that makes sense.

I already did a signal test and 10's all the way around.  (It's a small Christmas tree loop)

I don't have any more of the 8.4 volt batteries on hand right now without pulling something else apart, I assume a fresh 9 volt would work for a quick test - is that correct?

How is power being supplied, as you state in the first sentence of your second paragraph?  If the TIU is already on, and you then close a toggle switch top the block, the loco isn't getting a watchdog signal and starts in conventional,. with sounds on.

The thumbwheel issue could be the issue that sometimes causes the speed to go up instead of down or vice versa, randomly on each clock.  It may have been partially cured in the latest software release, which you have.  A shot of CRC QD Electronic Cleaner may held.  Note this particular product says platic-safe on its label.

Actually I do have a toggle switch involved - glad you mentioned it!!  I wanted to be able to run dcs or conventional with a regular transformer throttle.  So I wired the track to the center of a dpdt switch, the tiu to ones side and a z750 to the other side.  power to the bricks suppling the tiu and z750 were on a wall switch.  What I was doing was turning on the wall switch with the toggle in the center, and then turning on the toggle switch. 

I just went up to the layout and put the toggle to the tiu side first and then turned on the wall switch - every thing acted exactly as it should. 

What a simple thing - thanks a ton!

  And yes you can use a 9V battery as a test for a short period if a 8.4V rechargeable or a BCR is in question as the issue.  G