N Lenz decoder help

[mecgp7]

So I decided to bite the bullet a little while ago and get a DCC system. I have the Digitrax Zephyr. I've tinkered with it and can operate it on its most basic level. You may have followed my growing number of posts asking for help.

I bought two locos recently specifically with decoders which is a first for me as previously I didn't care. They are Atlas SD50s with Lenz LEO62XF decoders. Neither loco works at all. I disassembled one and put in a DC light board and it operates just fine. I investigated the issue online and it appears this can be an issue especially with this specific decoder and this specific chassis (SD50/60).

So, before I take a 5 lb. hammer to both locos, is there a step by step solution out there? So far I can only get the loco address read back by connecting the programming wires directly to the loco frames. Never while it sits on the track. Occasionally the light on/off will work. Other than that, nothing. When trying to read the address with the loco on the programming track I get the dnd error. Other DCC locos work just fine.

Are there step by step instructions to fix this? I need it broken down to: "Step one: press this specific button..."
Other solutions assume the user has experience which I clearly don't.

I'd appreciate any help.
Clint

[central.vermont]

Clint,
Sounds to me like you have a conductivity problem. First thing is are these new? If they are or not I would disassemble the trucks and clean the wheels and be sure the axle points and cups they sit in are clean. Also clean the very tip of the axle cups where they contact the wipers on the frame. And speaking of these wipers make sure that they are clean and fit snugly into the frame halves. Make sure that when they are in  the frame that they have an arch to them straight and are directly above the truck contact points.
Give this a try and let use know how you make out.


Jon

[mecgp7]

Jon,
Thanks. I did all of that and more. Even when I attach the programming wires directly to the chassis on either side of the decoder, I can only get the address. Attaching the track wires directly to the chassis results in nothing even when the address is entered.

According to some other online forums, they suggest putting a resistor between the programming rails or even a twelve volt light bulb. Not sure why this is supposed to work, but it has something to do with the system putting out more voltage. But if it will read the decoder when the wires are directly attached to the chassis then why won't it allow other functions? There is also mention of a Lenz factory reset, but I couldn't follow the lingo to make it work.

[central.vermont]

Clint,
Make sure you have a really good connection to the motor from the board. It sounds to me it's not seeing the load from the motor.

Jon

[mecgp7]

Yep. I checked that and even cleaned the decoder and motor leads. I checked and cleaned everything starting with the track and then up through the loco to the decoder. Like I said, the loco works perfectly with a DC board.

[mecgp7]

I can get the motor to respond in DCC by putting the leads directly to the decoder and putting the throttle on high. Makes me think my system doesn't produce enough voltage to get through to this particular decoder.

Time to punt and order DC boards.

[davefoxx]

No, get a Digitrax decoder before you give up on DCC.  I purposefully avoid factory installed decoders and install my own decoders of choice.

DFF

[jdcolombo]

Cleaning does not necessarily insure a good connection, and if you are not getting excellent continuity from the track to the board, you will have the problems you describe.   The usual place for failure in electrical continuity for these boards is where they attach to the frame (the "ears" of the frame that slip over gold contact pads on the board) and the connection to the motor. 

If you have a multimeter or something that can check continuity, do this.  Place the board in the chassis and then the chassis on a track with your track power off.  First, check continuity between the track and each side of the frame (with a multimeter, clip one wire to one rail of the track, turn your multimeter to its continuity check mode, and then touch your other wire to the frame on the same side  as the clipped rail).  Do you have continuity?  If yes, go to next step.  If no, then you've got a problem with pickup in your trucks.  Fix it (this is highly unlikely since the engine works with the DC board in it).  Make sure to check both sides.

If you have continuity between the track and the frame, the the next thing to check is continuity to the board.  If you have a multimeter with a pencil-point probe, leave it in continuity mode with one wire clipped to one rail.  Now comes the hard part.  On these boards one end has all the DCC components and the other end has several diodes.  If you look at the PC board traces, you will see that one side of the board has a trace that runs between the two frame pickup pads (they are gold plated) and then to a tiny surface-mount resistor on the DCC-component end.  You should be able to touch the end of the SMT resistor attached to that trace and get continuity.  On the other side, the trace connects the two frame pads and then connects to one of the diodes via a trace on the under side of the board.  What you want to do is touch your probe to the side of the diode connected to this trace (if your board is like mine, there is a tiny number on each diode; the diodes are arranged in a set of 3 near the LED, then two more.  You want to touch the diode in the set of two on the same side as the pickup pads you are testing, on the side of the diode with the number - the side that faces the LED.  But your board may not be laid out exactly like mine).

I think that what you may find is that the pickup pads on the board are not making good contact with the frame.  That is the usual problem. The fix is to put a thin coat of solder on the pads to "thicken" them for better contact with the frame.  Even if it seems like the fit is "tight" you'd be surprised how often there is a tiny gap that prevents good electrical continuity.

If you are getting continuity between the frame and the board, then the next potential problem is the motor pickups.  Make sure these are bent out so that they put pressure on the pads underneath (and make sure that each motor pickup is properly oriented so they are contacting the motor pads underneath; sometimes these get "twisted" so that they are not hitting the pads correctly).

If you do all that and it still doesn't work, then I'd buy a TCS Z2 decoder and hard wire the thing - which I do with all my diesels to avoid these problems (I use the light board for electrical pickup, cut the traces to the LED's and motor at the appropriate places, put the TCS under one end of the light board, and hard wire it to the power pickup traces, the LEDs and the motor).  You can buy a Digitrax or TCS board, but often these also have issues with "fit" where the pickup pads contact the frame. 

John C.

[mu26aeh]

If you need DC boards, I have quite a few.

[nstars]

A very common problem with the Atlas loco's is the connection from the motor leads tot the underside of the decoder board. This connection tends to be very sensitive and quit often the contact is very poor or besides the pads underneath the decoder. Make sure these leads do touch the pads on the underside of the decoder. Make also sure these motor leads don't touch the frame. They may only touch the decoder board. Some Kapton tape on the frame is a good way to insure this. The 3rd problem could indeed be the connection between the decoder board and the frame. When you insert the decoder in the frame it has to be a very light press fit. If it's too loose, a little bit of solder may help, but in my opinion this should be the last resort.

If all fails the Lenz decoder could be faulty which unfortunately I have some before. Personally I'm not a big fan of these Lenz decoders. I have seen some weird behavior from loco's with these decoders. In that case the best solution would be a replacement drop in decoder from Digitrax, TCS or NCE.

Marc

[central.vermont]

Clint,

One last step you could do is bench test the decoder. to do this you must remove the decoder and motor from the chassis and using alligator clips hook everything up and then see if you still have the same problem. This will at least eliminate some of the unknown. Be sure you have all connections isolated from one another so as to not have any shorts or you will let the magic smoke out. 

Jon