Unexpected speed variations Atlas S-2

[OldEastRR]

My Atlas S-2 has this strange slowdown then resume the original speed thing going. It seems to happen mostly at the lowest speeds (10-20 smph) and it does it regularly as it runs along.  I've had it for a while but only recently started running it extensively to test out all my locos on the newly-finished layout. Don't know if it acted like this before because I only ran it a few feet back and forth when I got it new. No other locos act this way but this is the only factory DCC Atlas I have.
I have an NCE PowerCab DCC system.

[Steveruger45]

I am assuming the decoder is an NCE.  If so I  have had this problem in the past.
The fix is to set up cv116 and cv117 for the torque compensation or dither rates.

Try setting cv116, the dither kick rate, to a value between 2 and 4 (a value of 1 gives continuous kicks a value of 6 gives lowest rate) factory default is 0 = off.
And then set cv117, the dither strength,  to a value of between 4 and 25 (max practical setting is 50) factory default is 0 = off.

I would try cv116 =2 and cv117 =25 to start with.

[OldEastRR]

I think the S-2 has a LokSound decoder.

[Steveruger45]

Yeah, thats correct,  the factory fitted sound ones are esu loksound for sure if albeit a specifically made one for the S2.
I’m not sure though what decoder was fitted to the non sound ones. 
I see you said you have an NCE system which I took for the decoder.  My mistake. 
IIRC the non sound ones are fitted with a six pin socket for a plug-in decoder on the Atlas S2.
I don’t have one, too old for my modeling era.
Assuming you checked the usual possible other causes with poor electrical pick up etc then it could be poor decoder contact at the six pin plug.
Do you have a lokprogrammer?

[peteski]

He didn't say whether the model has a sound decoder or non-sound decoder.  But I think that this loco was only sold with 2 options:  DC only (with no plug-n-play DCC capability) and the "Gold" version with a custom made ESU LokSound decoder.

[Steveruger45]

Hi Pete
I just checked spookshow and the S2 was made with dcc ready version with six pin decoder plug

Quote
The PC board on the DCC-Ready version is equipped with a European-style six-pin NEM 651 DCC interface (underneath the board, down towards the cab end). Other than the motor saddle and the PC board (and the fact that there is no speaker inside of the cab enclosure), everything else is the same as the DCC-Sound version.

[peteski]

Hi Pete
I just checked spookshow and the S2 was made with dcc ready version with six pin decoder plug

Quote
The PC board on the DCC-Ready version is equipped with a European-style six-pin NEM 651 DCC interface (underneath the board, down towards the cab end). Other than the motor saddle and the PC board (and the fact that there is no speaker inside of the cab enclosure), everything else is the same as the DCC-Sound version.

OK, but Al's statement "this is the only factory DCC Atlas I have" implies that the decoder was installed by Atlas (not installed by Al). So that means Sound decoders.  But I also think if the original problem statement included more details it would make troubleshooting easier.  We are making assumptions here.

[Steveruger45]

OK, but Al's statement "this is the only factory DCC Atlas I have" implies that the decoder was installed by Atlas (not installed by Al). So that means Sound decoders.  But I also think if the original problem statement included more details it would make troubleshooting easier.  We are making assumptions here.

Agree.  AL, pls let us know what decoder you have in your loco or at least if it is the esu factory installed sound one.

[OldEastRR]

The S-2 is the Atlas Gold version that came factory-equipped with DCC and sound. I've made no modifications to it, other than adjusted some sound levels.

[jdcolombo]

You should try the auto-calibration for the BEMF circuit.  Set the engine on the layout, where you have about a 4’ stretch of straight track.  Using ops mode programming set CV54 to zero.  When you exit programming mode, and the engine will take off like a banshee, then slow and stop.  The decoder will then reprogram the BEMF parameters based on internal measurements from this test.  Auto-Tune isn’t foolproof, but it often cures odd speed issues.

John C.

[RBrodzinsky]

When you exit programming mode, and the engine will take off like a banshee, then slow and stop. 

Should read "When you exit programming mode, press F1, and the engine....

[jdcolombo]

Should read "When you exit programming mode, press F1, and the engine....

I swear that sometimes my computer seems controlled by aliens.  I could have sworn I typed “press F1” . . .

John C.

[EL3632]

I have seen something similar to this happen with various non-sound decoders from various manufacturers. What I ended up finding out was a value for Vstart/mid/max was off (I.e. Vstart value was 180 when the Vmid was less). Read these from your decoder, if there is a value noticeably off, then adjust it accordingly. Vstart is usually set to 0 in pretty much every decoder I have seen. I am unsure exactly how to adjust/fine tune with the Vs as I always write a speed table. I am also unsure if this is even possible on sound decoders, however ESU does force Vstart & max to be used.
Just a random thought I had reading this thread.

[OldEastRR]

Yep ... incompatible V speeds. Works fine now.