TCS CN-GP Decoder Speed Step Issue

[tehachapifan]

I just installed the CN-GP in an older Atlas GP9 and everything works fine. However, I have a speed step problem (when my command station is set to 28 speed steps) where speed step 2 is slower than speed step 1, speed step 4 is slower than speed step 3 (but faster than speed step 2) and so on, although the phenomenon lessens at faster speeds. Adjusting CV's 2, 6 and 5 doesn't seem to resolve this, although I can lessen the variation some. I've found some previous discussions here and there that sort of touch on this, but not my particular issue directly. I also recall having this issue in the TCS decoder for I believe the MP15DC, which I guess I somehow resolved, although darn if I can remember what I did! (setting CV's 2, 5 and 6 the same as the MP15DC doesn't seem to help).

[jagged ben]

Have you contacted TCS?

I had issues with speed tables not working at all when I first got some of CN decoders (also analog conversion).  I have sort of put it down to them being from the very first release, but I have not bought any CN series since then, even though others have said they are good now.  I would love to love these decoders but they just don't seem that perfect. 

Sorry that doesn't speak to your question directly, but I guess my point is that if it's not behaving the way the instructions say it should, send it back.  TCS needs to help you solve these issues.

[tehachapifan]

Thanks but I kinda wanted to start here rather than going the send-it-back-to-the-factory route. Hoping there's a simpler solution with some sort of setting adjustment. As I mentioned, I had a similar issue in an MP15DC that has since been resolved, unless I'm thinking of the wrong loco.

[woodone]

Try setting the decoder back to factory defaults. Set CV 8 to 2. Then try running using 3 has an address.
If this works, then set the address to the number you wish.

[peteski]

That sounds like a similar issue TCS has with the Z2 decoder. When I spoke to the TCS rep at the Springfield show last February he acknowledged the problem and told me that they will be fixing the decoder's firmware.  That was for Z2  - not sure about the CN decoder.

[sp org div]

Hey Russ
What did you find?

I just installed my first CN-GP decoder (kato sd40) last week, and have multiple issues.
This preliminary set up is usually pretty easy stuff with all the other decoder manuf I am using... but I got the same speed step issue with the default settings (built in 7/2015 iirc).  I tried shutting off bemf to use dither which seems to have helped stabilize the throttle speed increment issue, but now it is real cranky at starting, and poor slow speed results (even after messing with the V and freq CVs).  Still have to experiment with it more, as someone recommended still using bemf, but shut it off as early as possible...
Then mine surges drastically intermittently when running slow (it will jolt from 10mph to 40mph and quickly revert back to 10mph)...  Reports are there should not be too large a spacing between the speed step settings or could cause this, but I had simply set CVs 2,5,6 similar to other locos that I have so they would all run together...?
Also this is by far the worst loco I have in my stable of 40 DCC locos as far as stalling issues (thoroughly cleaned all loco electrical contact points-twice, clean track).  The headlight doesn't simply blink over anomalies in the trackage like all my other units, but completely stalls far too often, to the point the loco is not worthy of participating in operations.  I am willing to let some slow speed ops go in exchange for a loco that does not stall every 3 feet, but sad at the thought of having to compromise at all.
FWIW, my Z2 performs pretty well overall in an SW1200 install, and it allows the headlight to blink over dirty trackage and recovers, rather than the Total Stall syndrome.
I thought I reset the CN-GP to defaults already, but after reading the above, will reset again and try it on addy 03 to make sure when I get home tonight...

Jeff

[tehachapifan]

Jeff,

I haven't messed with it much since I posted, but sorry to hear you're also experiencing issues. Looking forward to hearing how your continued experimentation goes. Funny you mention it, I also had an instance when I was originally trying to set CV's where the loco suddenly took off at a high speed. I grabbed it off the track before I thought to do anything else and it (thankfully) hasn't done that since.

[sp org div]

Ok
Reset the CN-GP decoder to defaults tonight. 
Still had the erratic speed step issue (throttle speeds 1 and 2 faster, 3 slows down, 4 and 5 faster, 6 slows down, etc). 
It still has significant dropping out, but seems to be better than before.  Now the headlight blinks over poor continuity conditions, or it frequently stops, but resuming quickly again (rather than totally stalling as before).  Still not to my satisfaction when comparing it to the rest of my fleet.
Next gave it a 4 digit addy (with 128 speed step).  Set CV02 @ 00, 06 @ 50, and 05 @ 100.  No change in erratic speed step issue.
Set bemf to shut off with CV10 @ 02 (so bemf shuts off when the throttle gets to speed step 2), which so far appears to have cured the erratic speed step issue...   It runs fairly well at slow speed also.
I have not noted a return of the sudden sprinting at this time...
I am content to know that 2 of the 3 issues are pretty much resolved, and can go back to fine tune settings more later.
Unfortunately I feel like I am at a dead end with the power drop out issue.  Maybe someone else can elaborate here.  I have 2 identical Kato locos that I just installed Lenz Gold decoders in that also exhibit the same power drop issue, but not as bad.  With my other Zimo and Digitrax equipped locos (same kato SD40-45), I do see headlight flicker, but they rarely drop out, which is acceptable to me.  Im about at the conclusion that the CN-GP and Gold decoders are just too sensitive to power loss.  It / they might need to be replaced with one of the proven decoders to just make it all go away...

Jeff

[peteski]

Jeff,
flickering headlight is a *CLEAR* indication of power pickup problem.  This is not something that can be fixed in the decoder (although if the decoder was equipped with a keep-alive circuit it would mask the pickup problems).

Different brands of decoders handle this type of problems differently.  Some will have large enough internal capacitor to keep the processor running and if the loco has enough inertia it will keep gliding through the trouble spots (buy you will see headlight flicker.  Other decoders will simply stall and have to reinitialize once the power pickup is restored. The time to reinitialize the decoder can also vary by brand. Some are fast enough to be almost imperceivable while others will take long enough to be seen as a hiccup.  The runaway loco could have also  been caused by poor electrical pickup. The power drops coudl have confused the decoder in such a way that it delivered full power to the motor.

Fix your electrical pickup problem and your locos will run much smoother.  Quest for perfect power delivery system is the reason modelers power up the frogs and hardwire points of turnouts - to assure as good of a power delivery system as possible.

[tehachapifan]

OK, I tried setting CV10 @2 like Jeff did and I initially experienced all kinds of speed fluctuations. Then the loco stopped responding completely and I discovered that one of the boards (rear) had become a bit loose in the frame. I already had added a little solder to the connecting pads for a tighter fit but that had apparently worn down enough to cause a connection problem. I have not added more solder yet but I repositioned the board where it makes a better connection so I could test things out more. Now I have very smooth acceleration, deceleration and overall running....except for a relatively persistent occurrence where the lights suddenly and briefly blink off and the loco takes off at least twice the speed. It stays at that speed until I bring it to a stop and start it over again from step 0. I hope that this is still due to an intermittent connection problem with the frame, for which I will try adding more solder to the pads. Keeping fingers crossed!

[sp org div]

Thanks for the update Russ
I will go back and revisit the board connections in hope that mine are also loose and causing the power loss / drop out issue...
otherwise I am at a total loss for this decoder's unreliability.

[tehachapifan]

Okay, mine is running well now. I made sure the decoder boards were both seated well but I was still having the issue of the lights eventually blinking off (without any previous flickering) followed by a marked speed increase. I then reset the decoder with CV8=2 and it still did it. So, I went back the beginning and looked at track and wheel cleanliness again, which I thought was all fine. Turns out the loco wheels were indeed starting to get dirty . I cleaned them up and the problem appears to be resolved. I think Peteski was right in that the pickup problem was possibly being masked and had the appearance of another cause. The odd speed step issue I was original having is also resolved, but I'm not sure which corrective step(s) fixed that.

[peteski]

Turns out the loco wheels were indeed starting to get dirty . I cleaned them up and the problem appears to be resolved. I think Peteski was right in that the pickup problem was possibly being masked and had the appearance of another cause. The odd speed step issue I was original having is also resolved, but I'm not sure which corrective step(s) fixed that.

Well Russ, there ya go!  Sometimes the fix is easy.    But seriously, flickering headlights are a sure sign of electrical contact issues (which should be resolved before attempting any more complicated solutions). And often the problem is with dirty wheels or track.

[tehachapifan]

Right. While I may be trying to save some face now, I wasn't experiencing flickering headlights in the normal, dirty track or wheel sense. I would have immediately picked up on that. Instead I had smooth, completely flicker-free operation for several seconds, then a more pronounced blink off and on followed by the speed increase. As you alluded to earlier, I think this decoder may mask power pickup issues due to dirty wheels or track really well until it just can't anymore, then it has a dropout...in my case followed by the speed increase.

[sp org div]

So I pulled it apart again to check the circuit board connections.  It is important that all 4 of the CN-GP decoder- to-frame electrical points are making good contact.  I had 1 out of those 4 points that was not making good contact.  The offending board was held tightly in place... but just by one side.  On closer inspection the opposing side was loose.  I tapped (with punch and light hammer) all of the frame "ears" down onto the decoder pick-up sections to insure that they were making better contact, and can happily report that stability is much better.   
Over freshly cleaned track it runs very well now.  Once the track sees a number of freights move around the layout, this unit's performance starts to deteriorate from dirt accumulation on the rails.  Then it is back to the blinking headlight and hiccup with resumption of speed, but no more complete stalling has been noted.  The Digitrax and Zimo decoders (currently installed in the same SD40/45 chassis) run well on the same track sections, with at worst a slight flicker of the headlight.  Maybe I am still missing something.... but a significant improvement at this point.

Jeff