TCS CN decoder - slows down on certain speeds

[Bart1701]

I have a TCS CN decoder installed in an older N Gauge Atlas GP35. I am running it on a Digitrax system. When I am using my DT402 throttle to control it, I notice that as I increment the speed value (as shown on the display), there are certain speed values where the locomotive will always slow down a bit from its previous speed, and then as I increment the speed again it will accelerate quickly for a brief moment (I would call it "lurching ahead").

Not much customization with the decoder was done outside of setting the loco address and adjusting the momentum settings. BEMF is activated by the default decoder values.

I had also turned on dithering and played around with those settings. I could see that things had changed, but still had issues (maybe more than before) with the lurching. Dithering is now turned off.

Any ideas on what could be causing it to slow down/speed up when advancing to certain speed values? One of the places this happens is at the lower speeds as the engine is moving slowly; it's annoying to see it creeping along nicely and then hitting the head wind that slows it down and then hits the tail wind that speeds it up.

Thanks,
Bart

[Steveruger45]

Are the speed step settings in the decoder and the dcc system you’re using set both the same?
28 vis-à-vis 128

[RBrodzinsky]

This is an old issue with TCS decoders, caused by a microcode bug. I know they fixed it, just not sure when

[peteski]

I have a TCS CN decoder installed in an older N Gauge Atlas GP35. I am running it on a Digitrax system. When I am using my DT402 throttle to control it, I notice that as I increment the speed value (as shown on the display), there are certain speed values where the locomotive will always slow down a bit from its previous speed, and then as I increment the speed again it will accelerate quickly for a brief moment (I would call it "lurching ahead").

Not much customization with the decoder was done outside of setting the loco address and adjusting the momentum settings. BEMF is activated by the default decoder values.

I had also turned on dithering and played around with those settings. I could see that things had changed, but still had issues (maybe more than before) with the lurching. Dithering is now turned off.

Any ideas on what could be causing it to slow down/speed up when advancing to certain speed values? One of the places this happens is at the lower speeds as the engine is moving slowly; it's annoying to see it creeping along nicely and then hitting the head wind that slows it down and then hits the tail wind that speeds it up.

Thanks,
Bart

I had this problem few years ago with their Z2 decoder (if you search the forum you should find that thread).  Others did too. TCS acknowledged the problem and said that it was caused by a bug in the decoder's firmware.  I suspect that your decoder used the same microcontroller as the Z3 and exhibits the same bug.  TCS stated that they fixed the bug and later production runs of Z2 work properly.

To be honest, I never followed up with TCS (as far as possible decoder exchange goes). I just don't use TCS decoders anymore (for that, and other reasons).

[Bart1701]

Thanks for the info, everyone!

I searched and found some other posts (including, I think, the one Peteski had mentioned). Glad to see that there may be an issue with the decoders, and not me!

I have emailed TCS to see what they have to say about this.

Thanks,
Bart