Help required with LGB 20841 Digital (Saxon IV K)

[Dan]

Has the original poster looked at the revision of the firmware to see if both 55021's are identical? There are at least 3 different versions of this decoder and can relate to bemf control as well as speed step limitations.

 

[Distrackted]

Has the original poster looked at the revision of the firmware to see if both 55021's are identical? There are at least 3 different versions of this decoder and can relate to bemf control as well as speed step limitations.

The decoders appear to be identical.

 

[Distrackted]

The decoders appear to be identical.

So I may have solved the problem. The motor for the faster (rear) truck had a resistance of 3.2 ohms. The motor for the other truck was closer to 4 ohms. I had a spare motor that measured about 3.8 ohms, so I replicated the motor in the rear truck with that one. The two trucks are closely matched for speed now I don't know if measuring the resistance is a thing or not for selecting matching motors, but it seemed to work in this case.

 

[Distrackted]

So I may have solved the problem. The motor for the faster (rear) truck had a resistance of 3.2 ohms. The motor for the other truck was closer to 4 ohms. I had a spare motor that measured about 3.8 ohms, so I replicated the motor in the rear truck with that one. The two trucks are closely matched for speed now I don't know if measuring the resistance is a thing or not for selecting matching motors, but it seemed to work in this case.

Thanks to everybody for all the helpful input!

 

[John Russo]

You could try removing the motors and then measure the rpms without any load.

https://www.amazon.com/AGPtek%C2%AE-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=asc_df_B004Q8L894/?tag=hyprod-20&linkCode=df0&hvadid=312152566480&hvpos=&hvnetw=g&hvrand=16691502844616827995&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9006782&hvtargid=pla-472577771481&th=1

 

[Distrackted]

You could try removing the motors and then measure the rpms without any load.

https://www.amazon.com/AGPtek%C2%AE-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=asc_df_B004Q8L894/?tag=hyprod-20&linkCode=df0&hvadid=312152566480&hvpos=&hvnetw=g&hvrand=16691502844616827995&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9006782&hvtargid=pla-472577771481&th=1

Thanks for the great suggestion. I have two new motors on order, but getting the tachometer seems like a good idea to make sure motors are a matched pair. Thanks for the link. Cheers!

 

[dunnyrail]

Thanks for the great suggestion. I have two new motors on order, but getting the tachometer seems like a good idea to make sure motors are a matched pair. Thanks for the link. Cheers!

The 2 new ones should be fine. One of the old ones likely to be perfect as well so your tachometer should prove which one. Would be handy to have in stock if a single motored loco goes funny. The faulty one could be repaired, there have been great threads in here how to do it. Well worth hunting out or if someone can provide the link?