I noticed today that the rear truck on my Genesis F7A loco is not receiving power to turn the gears.
I am having a hard time understanding how the decoder interacts with the motor on a DCC equipped loco,
I am getting power on both ends of the decoder where the pick up wires from the trucks connect to the decoder (NCE-DASR). So, how does this all work? Do the metal wheels pick up power from the tracks and transfer power to the decoder which in turn feeds power to the motor? Why am I not getting power to the rear truck to turn the gears and rotate the wheels?
The decoder has nothing to do with supplying anything to either of the trucks. The motor if run on DC receives electrical power from the rails through the truck pick ups… The motor if run on DCC receives electrical power from the decoder, which in turn receives electrical power from the truck pickups.
The motor than converts the electrical power into motive power which it transmits through drive shafts to the front and rear truck. If the front truck wheels are turning, but the rear truck wheels are not, then there is a mechanical connection issue between the motor and the gears for that truck.
maxman, thanks so much for that explanation. I don’t know why my brain cannot figure that out.
Power picked up from rails by metal wheels and onward through the decoder to the motor which then mechanically turns the gears mounted on the wheelset axles. Duh.
I do have another question in this regard.
First, for what it is worth, I misspoke. It is the front truck not the rear truck that it not picking up power.
But here is the thing. When I pick up the rear truck off the rails, there is no movement indicating that there is no power from the front truck. Yet when I test for power from the front truck on the decoder, I get a positive reading. When I put jumpers from the rear leads on the decoder to the front leads, everything works fine. So does this indicate that there is a problem with the power pick up wires at the truck connection? And, if so, why am I getting a reading on the front leads of the decoder where the front pickup wires connect to the decoder?
It is probably,a bad connection,of the wire that is soldered,to the pick-up bar on the truck,happens a lot,the wires are so tiny… Do a continuity test from the decoder,to the bar,if you don’t get a reading,it’s the wire,either on the bar,or the decoder…
I’m not sure I followed all of your explanation, but so far as the decoder’s track connections go the pair of connectors on the front of the decoder and the pair at the rear are, I believe, in parallel. So if either pair of the truck pickups are connected, you will read a voltage at both ends of the decoder.
You will even get a voltage reading if only one pickup from each truck is connected, so long as they are from opposite rails.
So, I believe that you do have a continuity problem from on of the trucks. You found this by lifting one end of the loco. However, sometimes if you are not careful you will inadver
OK, thanks guys, it may be a loose wire connection at the truck so I will check for continuity.
maxman, I think you did understand my somewhat garbled explanation correctly, and I thank you again.
Frank, thanks to you too.
maxman, you are probably right about a power reading on the front decoder leads due to the working power pickups from the rear truck. I hadn’t thought of that.
I did read about an Athearn Genesis pickup problem at the following site.
If you lift the rear truck, then there is no power to the decoder from the rear truck. If you see power at the front of the decoder with the rear truck lifted, that means that the front truck is picking up power.
You originally said that the wheels of the rear truck were not turning. Now you say that there is no movement with the rear truck lifted but there is power present at the front of the decoder. So I’m confused. If the engine is sitting on the track, do any of the wheels turn?
maxman, in my original post, and in the title to the thread, I said that there was no power being picked up from the rear truck. But, I had confused myself, and as I stated in a follow up reply, the rear truck pick up wires are fine. It is the front truck that is the issue. Sorry for that confusion.
But, since my original post, with your comments and advice, I dug into this problem deeper and came up with the following conclusions.
There is definitely power being picked up by the wires on the front truck and transferred to the front leads on the decoder. However, the decoder is not recognizing power from the front truck. I say this because when I pick up the rear truck off the rails, there is no movement of the loco whatsoever. No lights, no nothing.
One other thing that I did was to temporarily remove the front pickup wires from the decoder and clip a light bulb on the pickup wires. With the rear truck lifted off the rails, there is no movement, no loco headlights, but the temporary bulb is lit. So there is definitely power to the decoder, but the decoder is not recognizing the power from the front truck.
Thanks for the diagram…Not being in DCC,I don’t look at them much…I wish they had a schematic of the whole circuit. But I doubt,they would do that and give their secrets away…You wouldn’t happen to have a similar decoder on hand,to do a test with??
maxman, in my original post, and in the title to the thread, I said that there was no power being picked up from the rear truck. But, I had confused myself, and as I stated in a follow up reply, the rear truck pick up wires are fine. It is the front truck that is the issue. Sorry for that confusion.
But, since my original post, with your comments and advice, I dug into this problem deeper and came up with the following conclusions.
There is definitely power being picked up by the wires on the front truck and transferred to the front leads on the decoder. However, the decoder is not recognizing power from the front truck. I say this because when I pick up the rear truck off the rails, there is no movement of the loco whatsoever. No lights, no nothing.
One other thing that I did was to temporarily remove the front pickup wires from the decoder and clip a light bulb on the pickup wires. With the rear truck lifted off the rails, there is no movement, no loco headlights, but the temporary bulb is lit. So there is definitely power to the decoder, but the decoder is not recognizing the power from the front truck.
The two motor outputs ont he decoder as just linked by circuit board traces though, it’s not like there are two actual motor drivers on the decoder.
Athearn has a HUGE problem with their power pickup, I have two RTR RS-3’s, and one STILL does not have reliable power pickup from the one truck, despite my soldering additional wires right to the metal sideframes from the decoder. The other one - had no issues at all. It seems the root of the problem is that the plastic part of the truck contacts those little square brass bearings before the metal part of the sideframe - thus, no power is transferred at that truck. Easy to demonstrate, set one truck on a piece of paper, leaving the other fully in contact with the rails - the loco should still get power and move. Repeat with the other truck - again, it still should run. If it doesn;t, the truck NOT on the paper has a power pickup problem
I’ll get around to fixing the one that doesn’t run. either by filing away some of the plastic or soldering some fine wire right to the brass bearings. Low priority because the one that runs, I just picked up the cheapest one on eBay I could find, and swapped shells, so I don’t have a shell I’d want to run for the other chassis if I did fix it.
What’s bad is that this carries over to the supposedly higher quality Genesis line too.
maxman, there is no mechanical problem. I was mistaken when I reported that.
[quote user=“maxman”]
With the loco sitting on the tracks and the wires from the front truck disconnected from the decoder, can you read a voltage across the left and right rail pick ups as shown on the decoder diagram? I think I’m going to stand by my opinion that the front and back motor pickups are in parallel until someone tells me that there is something on the decoder to prevent this.
Taking this one step further, I have a new DA-SR in front of me. Looking at the backside, there is what appears to be a relatively wide copper trace that connects the front and rear right rail pick up connections, and a similar trace for the left rail pick up connections. Without any wires connected, I checked for continuity between the front and rear right rail connection tabs and found that there is a direct connection. I found the same checking between the left rail connections.
You can do the same check by disconnecting the rear pickup leads like you did for the front. If you get continuity between those points, then I am of the opinion that the decoder is okay, a least as far as the not recognizing the power from the front issue goes.
Also, I don’t know what those extra motor output connections are for, and the instructions don’t seem to mention them. However, looking a
