Decoder Compatibility Problem?

[rjmusto]

Hi,
I have fitted a Kuehn NO25 decoder (German company) to a loco for a friend of mine.

On my layout, with a Roco Multimaus command station it operates perfectly.

However, on his layout, which uses a Bachmann E-Z Command, the loco behaves rather erratically. At start up, it stutters, stop- starting and the headlights flash until a kind off 'sweet spot' is reach where it runs smoothly. Same thing happens as it slows down.

I'm guessing this is some kind of communication miss-match, although the CV settings I have look pretty normal.

Anybody know what the likely cause of this is?

Thanks a lot.
/r

[richg]

This seems to indicate dirty track. Has the track been cleaned, not looks clean but has any actual cleaning been done?
I am not familiar with the decoder.

Rich

[richg]

I did some searching for this decoder and seems to be NMRA compliant. Many of the links are in German but I did see a reference to NMRA. I could have used Google translation but the reference to NMRA seems sure.

Google can be your best friend. There are other search engines.
Never forget people, we have at our finger tips the biggest library in the world and we do not have leave the house to look through the library.

Rich

[rjmusto]

Thanks for the reply Rich.

I wondered about dirty rack also, but don't think it can be as he has another loco (that was DCC fitted) and it works fine.

I have an English copy of the Kuehn decoder manual and can't see anything unusual.

Is the EZ Command set to 28 speed steps? The manual for it has very little information and nothing on changing speed steps....

/r

[richg]

Ok, you did not say anything about a loco running ok on his layout which is why I suggested dirty track.

No idea about the EZ Command controller. I am totally impressed that you actually took time to read the manual. Most do not.

Rich

[Jim Banner]

A couple of thoughts:

Be sure the decoder is in 28/128 speed step mode.  Flashing lights that occur randomly are almost always erratic pickup.  Flashing lights that occur as you turn the throttle up or down are usually a speed step mismatch.

Be sure the decoder is set for DCC only.  If it is reverting to Motorola Trinary on loss of signal, it may be exaggerating the effects of minor power losses due to dust on the rails.

There has been no mention of what type of locomotive you installed this decoder in.  I assume you did a stall current test before the installation and found the stall current to be less than .7 amps.  If the stall current is close to or even exceeds .7 amps, you may be seeing the effects of different voltages on the rails.  I could find no specifications in the manual for your Roco Minimaus and am left wondering whether it regulates track voltage or not.  I suspect it does not.  Depending on what you use for input power, its track output voltage could be toward the lower end of the acceptable range for DCC.  The E-Z Command is known for being toward the high end of the range - some people moving up to a more comprehensive system complain that their trains no longer run like slot cars.  What I am thinking here is that the decoder may have marginal cooling and/or current limits for the particular application.  With the higher voltage from the E-Z Command, the decoder may be intermittently going into thermal or over current shutdown until the speed and current draw get high enough to reduce the track voltage to a more acceptable range.

If the locomotive in question was manufactured by Bachmann, make sure that the RFI capacitors have been clipped or removed.  With your Kuehn NO25 decoder, you can alternately set the motor drive frequency to 120 Hz instead of 16 kHz.  Bachmann locomotives with the capacitors still in place can have problems with high frequency "silent drive" decoders and when they do, the problems can be erratic, appearing and disappearing depending on the DCC system, the configuration  of the layout, and how much sugar your grandmother uses in her tea.

If the problems continue, take a peek under your friend's layout and see how he has done his track wiring.  Some configurations are more susceptible to "ringing" than others.  Running a DCC bus in a closed loop or eliminating bus wiring completely can be particularly troublesome once the size of a layout exceeds a couple of sheets of plywood.  One test you might consider doing is connecting his E-Z Command to your layout and seeing how it runs his locomotive there.  You might even want to make the testing more comparable to earlier tests by using the same number of his locomotives on your tracks during the test.

Bottom line, there are many variables involved.  If you can change just one thing at a time, you will have a much clearer understanding of what might be causing the problem.  And if you would be kind enough to let us know what you find, we will have a better understanding of this curious problem as well.

Jim    

[rjmusto]

Jim,
Thanks a lot for your detailed response.

The loco is a Bachmann make he purchased from the States and was 'DCC Ready'. I'll check up on the actual model number.

The decoder is set for 28/128 speed steps but including DC capability, so I'll change that to DCC only.

I'll check on the capacitor issue too.

More anon....

Ralph

[rjmusto]

Hi Folks,
Just to close this one down:

It was the suppression capacitor that was the problem. With it removed all is ok. 

Incidentally, the decoder installation sheet recommends leaving the suppression components in place.....

Anyhow, thanks for the help.

Ralph

[richg]

Hi Folks,
Just to close this one down:

It was the suppression capacitor that was the problem. With it removed all is ok. 

Incidentally, the decoder installation sheet recommends leaving the suppression components in place.....

Anyhow, thanks for the help.

Ralph

Many on the other side of the "Pond" believe the caps "should" be left in. They figure the caps "must" be needed to suppress possible interference.

Rich