Help required with LGB 20841 Digital (Saxon IV K)

D

Distrackted

Registered
Country flag
Hi there,

I recently acquired a beautiful, used LGB 20841 locomotive. It is the digital version with direct decoder interface and a pair of LGB 55021 decoders installed on the motherboard. I added sound (Massoth eMotion S) and replaced a couple of missing detail items with the help of Train-Li (USA). I also replaced the traction tire on the rear truck.

The problem I am having is that the rear truck seems to be spinning its wheels very noticeably in MTS (DCC) mode, even though that is the truck with the traction tire. When I run the locomotive in DC mode, the front and rear trucks appear to operate at essentially the same speed. Both 55021 decoders share a common track power source, but I assume each controls a separate motor.

I use the Massoth Service Tool to set the CVs and I use the 55021/22 template assuming that both decoders appear as a single 55021.

There was initially a small quartering error in the front truck which caused it to be a bit jerky, I corrected that and both trucks run very smoothly now. I'm thinking that because they both run at the same speed in analog mode, there is nothing wrong with the motors?

Does anyone have any thoughts on why the front and rear truck speeds would be different in digital mode?

Thank you!
 
Could it be trying to program both at once caused some issue? All my two motor loks have 3 amp or better motor current decoders installed and don't require two decoders. Maybe try unplugging one decoder, doing a factory reset, then doing the same for the other decoder. This might give you a starting point where everything is "equal". Hopefully someone with more specific experience will chime in.
 
phils2um said:
Could it be trying to program both at once caused some issue? All my two motor loks have 3 amp or better motor current decoders installed and don't require two decoders. Maybe try unplugging one decoder, doing a factory reset, then doing the same for the other decoder. This might give you a starting point where everything is "equal". Hopefully someone with more specific experience will chime in.
Click to expand...
Thank you for that suggestion. I just finished taking both decoders out and putting them on the Massoth decoder service board I have. I read all the CVs from each, and they were identical. When I put them back in, I also swapped their positions as a further check. That didn't change anything and the rear truck is still running about 50% faster than the front. I have just changed the motor in the front truck for a different one and am about to see if that makes a difference. I'll post an update when I find out. Thanks again!
 
Distrackted said:
Thank you for that suggestion. I just finished taking both decoders out and putting them on the Massoth decoder service board I have. I read all the CVs from each, and they were identical. When I put them back in, I also swapped their positions as a further check. That didn't change anything and the rear truck is still running about 50% faster than the front. I have just changed the motor in the front truck for a different one and am about to see if that makes a difference. I'll post an update when I find out. Thanks again!
Click to expand...
Hello again, changing the motor in the front truck helped somewhat, but the speeds still don't match exactly and this is bound to cause wear to the wheels and track. Any thoughts as to whether newer replacement decoders such as the Massoth eMotion L would be better at managing the motors, than these probably early LGB 55021 decoders? Our how to select matched motors? Thank you for any ideas you may have
 
While you have the loco opened up can you unplug the motor blocks and power them directly from the same DC source to check how out of sync they are? In my experience the motor blocks in two motor locos will run at somewhat different speeds for a given voltage and start at somewhat different voltages. I think this is one reason why the factory setting for the start voltage CV is typically set between 3 and 6 rather than zero on LGB locos. It makes sure there is enough starting voltage to ensure both motors start turning immediately.

You have probably already considered this but is there some issue causing a lot more drag on the slower set of drivers?
 
phils2um said:
While you have the loco opened up can you unplug the motor blocks and power them directly from the same DC source to check how out of sync they are? In my experience the motor blocks in two motor locos will run at somewhat different speeds for a given voltage and start at somewhat different voltages. I think this is one reason why the factory setting for the start voltage CV is typically set between 3 and 6 rather than zero on LGB locos. It makes sure there is enough starting voltage to ensure both motors start turning immediately.

You have probably already considered this but is there some issue causing a lot more drag on the slower set of drivers?
Click to expand...
Good ideas. Fortunately this is a very easy locomotive to work on! Only 6 easily accessible screws and the shell is off.
phils2um said:
While you have the loco opened up can you unplug the motor blocks and power them directly from the same DC source to check how out of sync they are? In my experience the motor blocks in two motor locos will run at somewhat different speeds for a given voltage and start at somewhat different voltages. I think this is one reason why the factory setting for the start voltage CV is typically set between 3 and 6 rather than zero on LGB locos. It makes sure there is enough starting voltage to ensure both motors start turning immediately.

You have probably already considered this but is there some issue causing a lot more drag on the slower set of drivers?
Click to expand...
Good ideas! Fortunately this is a very easy locomotive to work on. Six easily accessible screws and the shell is off. I'll open it up again tomorrow and try running the trucks one at a time of a DC source to see if they differ.

I had originally thought that the front and back trucks were the same but mirrored, with the cylinders facing opposite directions. However, looking again I see they are quite different in the way the ruining gear is configured to the wheels.

Nothing seems to be tight or binding on either truck. What perplexed me though is why the problem is so much less apparent running in DC mode on the track.

Thank you again for your advice.

Cheers
 
If all else fails I suppose you could program separate speed curves for each decoder. I'd make sure they were both linear without a knee (CV29 speed table bit off and the mid-speed CV halfway between the start and max speed CVs).
 
Distrackted said:
Nothing seems to be tight or binding on either truck. What perplexed me though is why the problem is so much less apparent running in DC mode on the track.
Click to expand...
This is baffling!

The fact the slow motor block did not change when you swapped the decoders seems to rule out the decoders too!

You said you changed the motor in the front (slow) motor block with only a minor improvement. But did you try swapping the motors if you can? Are they are the same?(To my knowledge they always are.)
 
Last edited:
phils2um said:
This is baffling!

The fact the slow motor block did not change when you swapped the decoders seems to rule out the decoders too!

You said you changed the motor in the front (slow) motor block with only a minor improvement. But did you try swapping the motors if you can? Are they are the same?(To my knowledge they always are.)
Click to expand...
No I didn't try just swapping the front and rear motors, but that is a really great idea! I'll try that next to see if the problem stays with the truck or goes with the motor. Thanks!
 
It sounds very much like one of the motors is partially shot. I had this to a certain degree with my Green one that had 2 x 55021 decoders. I bought 2 new motors and installed them, problem resolved. The benefit of tgis was that I had 2 spare motors one being perfect the other not so but still very usable.
 
dunnyrail said:
It sounds very much like one of the motors is partially shot. I had this to a certain degree with my Green one that had 2 x 55021 decoders. I bought 2 new motors and installed them, problem resolved. The benefit of tgis was that I had 2 spare motors one being perfect the other not so but still very usable.
Click to expand...
I also recently acquired a used LGB 20390 railcar( just one decoder in that one). On arrival I discovered it had a dead motor in one of the trucks. Just to be safe I ordered two new ones and replaced both. Upon inspecting the dead one a while later, I noticed a fair amount of oil or grease on the shaft near the bearing at the end with the contracts. On a whim, with nothing to lose, I sprayed a fair amount of fluorocarbon contact cleaner through the motor. Lo and behold, the motor starter to work perfectly again. Obviously the brushes and armature had been contaminated with the oil or grease. So now I have not one, but two perfectly good spare motors
 
I should have added that I restored operation to one of the motors in my ancient LGB 2040 baby croc by spraying the hell out of it with contact cleaner. I sprayed the other one too just to be fair!
 
phils2um said:
o_O Climate Destroyer! - Just kidding - but I hope you are using the newer, more climate friendly contact cleaners.
Click to expand...
That's a valid concern. It is indeed a very new aerosol can of contact cleaner, and I trust not as bad for the atmosphere as older formulations. I seldom have a use for it.

MG Chemicals, Electrosolve Contact Cleaner

Mainly light alkane hydrocarbons by the label, but also contains some 1,1,1,2-tetrafluoroethane.

It is CARB compliant whatever that means in this regard.
 
We used to have five gallon drums, on a stillage (ordinary tap!) and would run it like water, to 'clean' our arms when greased-up.. :oops::eek:
It did used to 'dry' your skin out :rolleyes: a little..

Once I realised just what the 'de-greaser' was, I was a lot more circumspect with it.
A different age..
At least one of the fitters, would be sucking on a Woodbine (cigarette) whilst using the stuff!

PhilP
 
(Ooops! Wrong thread..)


Good morning, All!
Sunny, but a little cooler, with a breeze.. Predicted to go back into the low 30's next week.
We seem to be (just) on the edge, of how far the rain is getting down the country, but could do with more.

I have been making sure it will be worth the Postie walking down the cul-de-sac.. Many 'bits' are on order, and plans being made.. :wondering::nerd:
Could be an interesting couple of weeks.

PhilP
 
Last edited:
We had the exact same issues here in New Zealand with 5 locos of the same model after talking with factory and suppliers we were told to replace the motor which solves the problem. Don
 
mradd said:
We had the exact same issues here in New Zealand with 5 locos of the same model after talking with factory and suppliers we were told to replace the motor which solves the problem. Don
Click to expand...
Thank you for that information. I had ruled out the decoders since switching the two to opposite positions on the main board didn't make a difference. I thought I had also ruled out the motors since I took the two trucks off and ran them down the track on DC and they went at about the same speed. So I was leaning to a problem with the main board, but then I just reversed the two motor connectors on the board and the rear truck still ran faster. So it must be the motor (s). It's such a nice locomotive I guess it's worth the expense just to replace both

Thanks again!
 
You must log in or register to reply here.
Back
Top Bottom