decoder installation

[pdlethbridge]

I am in the process of totally converting my layout to dcc. I was using the atlas controllers and selectors for a very basic small layout. It worked well with MRC power pack and analog engines. Now I'm using the NCE pro cab as my cab and have installed a digitrax 123 with the clips for a Athearn unit. It doesn't run. Now I have checked all connections, checked for broken wires, but I can't get the engine to run. Can I turn the cab on and short the track with a 12 volt bulb to check the cab? Is there anything I've missed? I added electrical tape under the motor for extra protection in case the lower clip pops off. I've been at it for a couple of hours and I'm getting brain cramps now. I think if this keeps going, I'll end up like Yampa bob!

[pdlethbridge]

I tried the bulb across the track so I know the pro cab is working. I'll do a step by step on the engine next

[Jim Banner]

A couple of thoughts -

Have you tried resetting the decoder?  I know decoders are supposed to come with certain default values programmed in, including CV1 = 3, CV19 = 0 and CV 29 = 6.  If any of these are incorrect, then your locomotive will not run on address 3 as you are probably expecting.  A quick way to tell the difference between motor problems and address problems is to see if the headlights work on the expected address.  If they do not, use a test light (a 12-16 volt GOW lamp will do) to check that the decoder is receiving power from the rails.

If the lights work as expected but the motor does not, it could be that a short or overload has damaged the decoder.  I assume you measured motor isolation with an ohmmeter and the motor current at 12 volts with the shaft locked.  Because of their small physical size, the DZ123 and DZ125 decoders are easily damaged if operated outside their comfort zone.  Digitrax gives two current ratings.  The lower one is the maximum average operating current.  The higher one is a "do not exceed, ever, for any reason whatsoever, not, never, no time" current rating.  Sometimes shorts occur intermittently, thus the importance of making sure the locomotive runs well on dc before converting  it to DCC.  A momentary short on dc is often harmless.  The same momentary short on DCC can be fatal for the decoder.

A third thought - any chance that a brush spring launched itself into outer space while you were installing the new motor clips?  This also will result in a motor that will not run, even though the lights work as expected.

As far as your other problem is concerned, I am afraid you will have to solve it yourself.

[pdlethbridge]

On the installation, I carefully  removed the clips, springs and brushes. The motor was removed and I prepared the frame by putting electrical tape under the motor in case a clip popped off. I had to reshape the clips  ( Gray on the bottom and orange on top )as they were touching the flywheels. With the brushes, springs and clips on, I attached the red wires and clips to the wheel clips and the black wire and clip to the frame. I put it on the track... NOTHING

[pdlethbridge]

AH  HA! I found out the problem. I was entering 003 rather than 3. Now it works. I'm off and running.

[Jim Banner]

Congratulations!  Can we assume from your findings that NCE considers 003 as a 4 digit address? 

[pdlethbridge]

must be. But I found that info in their manual. I guess my skills in building computers helped. I had, during this last round of testing, checked all wires on the plug. With everything working, it had to do with the decoder itself. I know there were no shorts in the system but there could have been a broken or loose wire. Reading the manual is always a good last resort that really should have been first.

[Yampa Bob]

Well, I sure am glad you got it fixed!!         

[pdlethbridge]

Me too. I didn't want to get the Yampa Bob disease!

[pdlethbridge]

This afternoon I installed a decoder on my walthers 90' turntable. It works great. Very easy install. Gray and orange to the turntable motor, red and black to power. This could be done with the atlas turntable, but I'd check the stall current if you wanted to use a decoder on a Bowser turntable.
The install this afternoon only took an hour, mostly rearranging existing wires. The Digitrax AR1 auto reverser is the next thing to install on the turntable. That should be here in a few days.

[Mike]

Am I missing something here? Why would you need a reverser on a turntable while using DCC? Are you basically (very basically!) considering the turntable to be like a reversing loop as it reaches a given point?- Mike

[pdlethbridge]

The tracks on the bridge would be considered like a reverse loop. If the left rail is + and the right is -, if the bridge were turned 180 degrees then the left rail would be - and the right + causing a short as soon as you move off the bridge. The lead in and exit tracks would stay left+, right-

[Mike]

Not to be argumentative, but rather to understand this. Since you are talking DCC, and the tracks are AC powered, would you really be talking + and - , or would it really be a matter of matching phasing of the AC?- Mike

[pdlethbridge]

just like dc, it would short  zitttttt

[Jim Banner]

Mike, first off, matching phase is the correct term to use with DCC although matching instantaneous polarity could also be used.  However, most of us here are not electricians or electrical engineers by trade so those that are usually cut the rest of us a little slack.

Turntables are usually wired in one of two ways.  One scheme uses a split pit rail or a split ring hidden within the model to automatically reverse phase/polarity twice within one revolution of the turntable.  As long as the reversals occur between approach tracks, the polarity/phase of the turntable can always match the approach tracks.  The Atlas 9" turntable is an example of this arrangement. 

The other scheme uses a one piece pit rail or equivalent ring for picking up power for one rail and the centre post or possibly a second ring for picking up power for the other rail.  Thus one end of the bridge will always match the phase/polarity of the approach tracks and the other end never will, unless you somehow reverse the connections to either the bridge or to all the approach tracks.  One way to do this is to use a detector to monitor which way around the bridge is and set the bridge phase/polarity accordingly.  Another is to set the polarity/phase manually with a switch.  Today, the most common way is to use a DCC auto reverser to match phase/polarity, and yes, it works with dc as well as DCC if certain conditions are met.