DCC conversion issue

[FEC]

I converted a very good running analog N scale Atlas MP15DC loco to DCC with a Digitrax DN163A3 decoder. After installation the loco runs really great forward at all speeds, but driving the loco backwards and problems get started, the loco drives really jerky at all speeds.

I reinstalled the decoder because I maybe installed the trucks not in the proper way but that didn’t help either. Played with CV values to smooth out the loco, clean track, ... I’m outta of ideas, could there be something wrong with the Digitrax decoders? This is my second loco that is having this issue, the other one is a Micro-Trains SW1500. Kato and Walthers conversions with Digitrax run great without a problem in both directions. Anyone who could solve my issue? Thanks in advance. Bruno

[peteski]

If the model didn't run at all in one direction that would most likely be a problem with the decoder, but jerkiness in one direction seems a bit odd.

Is this one of the locos where the motor contacts connect to pads on the decoder?  If yes, then maybe when the model runs backwards the motor's torque rotates it slightly - enough to cause intermittent contact with the pads on the decoder (making it run poorly)?

Have you tried to reinstall the DC board and see if it still runs well in both directions on DC?

[FEC]

Yes, it’s a motor contact to decoder pad install, made sure motor contacts make good contact with the pads. Reinstalling original DC board results in loco running just fine in both directions. I also tried to add some solder to the decoder pads to make better contact but didn’t help either. It’s a mystery why the loco only wants to run really good in one direction. Backwards it runs, then slows down (without doing a complete stop however), runs again, ...

[nickelplate759]

A shot in the dark here...
Is this problem happening when running on DCC or just straight DC?      I have problems with Digitrax dual mode decoders in DC mode not regulating speed well, but in both directions not just reverse.  Drove me nuts until I realized it was the decoder and not the mechanism.

[MK]

I just did one last month.  Everything went fine until about two weeks after the install I noticed that if I pressed lightly on the shell, the headlights go out.  Opened it up and added solder to all 4 pads and viola!  However, unlike yours, at no time did it run jerky, DC or DCC.  I too used the same Digitrax decoder but it was bought years ago and put in storage.  It had the old red tag on the bag with a price of $19.95!   

I think the instructions said to trim the motor tabs to avoid shorting but I didn't have to do that.  Unrelated, but maybe pull the motor tabs up a bit to give it more spring force to the board?  Also, try tapping on the shell and see if your lights go out.

Another thing is to watch out for the plastic piece which I'm guessing is used to block the light.  There's a little tab on the bottom.  Make sure it's not rubbing the lead screws.  It's the black rectangular thing on the frame.





Have you tried resetting the decoder?

[AKNscale]

@peteski- these are the models with the horrible wire motor tabs that lose their spring quickly.

@FEC I have 4 of these and ran into the same problem in my conversions. Check your motor tabs, you might have to cut them and hardwire the motor to the board. That's how Atlas rectified this model's poor running habits on the last run. Another problem these had is with the motor itself....

[FEC]

Loco will not run on DC with the decoder installed.
Thanks for all the offered solutions but have tried them all, except soldering the motor contacts to the decoder pads. Those motor contacts are so thin and fragile, these are the smallest I have ever seen. Will try to see if that helps.

[woodone]

I just did one last month.  Everything went fine until about two weeks after the install I noticed that if I pressed lightly on the shell, the headlights go out.  Opened it up and added solder to all 4 pads and viola!  However, unlike yours, at no time did it run jerky, DC or DCC.  I too used the same Digitrax decoder but it was bought years ago and put in storage.  It had the old red tag on the bag with a price of $19.95!   

I think the instructions said to trim the motor tabs to avoid shorting but I didn't have to do that.  Unrelated, but maybe pull the motor tabs up a bit to give it more spring force to the board?  Also, try tapping on the shell and see if your lights go out.

Another thing is to watch out for the plastic piece which I'm guessing is used to block the light.  There's a little tab on the bottom.  Make sure it's not rubbing the lead screws.  It's the black rectangular thing on the frame.
That little tab is a frame spacer- keeps the two frame half's from touching one another.
As for the motor tabs- Cut them short= solder shirt jumper wires to them, insulate with shrink and then solder the jumper wires to the decoder pads.





Have you tried resetting the decoder?

[peteski]

Loco will not run on DC with the decoder installed.
Thanks for all the offered solutions but have tried them all, except soldering the motor contacts to the decoder pads. Those motor contacts are so thin and fragile, these are the smallest I have ever seen. Will try to see if that helps.

As others said, reset the decoder and see how it runs. Resetting should also enable the DC mode (since that is usually the default setting), so you can try running it with the decoder on DC (I use a 9V battery as a source of smooth (non-pulsed) DC to eliminate any possibility of confusing the decoder.

If the decoder still doesn't run on DC, enable the DC conversion bit in CV29 (or verify that is is set by reading CV29 and verifying that bit 2 is set), then try it on DC.  See https://ncedcc.zendesk.com/hc/en-us/articles/200537669-CV29-Explained

[OldEastRR]

Aha! The answer is simple! It's a Digitrax decoder -- period.
Tho in fairness I will say MRC decoders apparently are worse.

[FEC]

Ok so this morning I did a factory reset and this time the loco would run in DC mode. I took the loco to the workbench to start the soldering of the motor contacts to the pads. Took the magnifying glass and made a sad discovery

[ Guests cannot view attachments ]

[ Guests cannot view attachments ]

The shell has melted, the backward led or a component near it went so hot I nearly burnt my fingers and it melted the shell of my newly purchased MP15DC. So not only the jerky backwards driving was an issue, also the led/component(s) on that side became hot. I’m so dissapointed, so I thank Digitrax for this?

Put the original DC board back in and loco runs fine, but will be collecting dust since I cannot sell it this way.

[FEC]

Aha! The answer is simple! It's a Digitrax decoder -- period.
Tho in fairness I will say MRC decoders apparently are worse.

I’m fairly new to DCC but have had so many problems with the Digitrax decoders, and now a melted shell, that I no longer will be buying one.

[crusader27529]

What value resistor(wattage and resistance value) was used for the LED in question? The LED would be very bright with a too small value resistor, and probably fail quickly. When the LED worked, was it very bright?

The amount of current that it would take to heat a resistor to a point of melting the plastic is significant. With 12V on the blue lead, and 20ma of current, yields about 1/4 watt. I don't know what size resistor was used, but operating a 1/4 watt resistor at maximum would require some space to allow the resistor to transfer that heat away. If the resistor is touching the plastic, most of that heat will be transferred directly to the plastic. If a 1/8 watt resistor was used, it'd get hot quicker, and then probably fail.. 20ma is high for most LEDs, and many will generate sufficient light with much less current.

So, I doubt that the melted shell was caused specifically by a Digitrax decoder. Personally, I don't like Digitrax products, but the decoder porbably had nothing to do with the melted plastic.......the rest of your problems could be caused by the decoder or other factors.

[woodone]

Ok so this morning I did a factory reset and this time the loco would run in DC mode. I took the loco to the workbench to start the soldering of the motor contacts to the pads. Took the magnifying glass and made a sad discovery

(Attachment Link)

(Attachment Link)

The shell has melted, the backward led or a component near it went so hot I nearly burnt my fingers and it melted the shell of my newly purchased MP15DC. So not only the jerky backwards driving was an issue, also the led/component(s) on that side became hot. I’m so dissapointed, so I thank Digitrax for this?

Put the original DC board back in and loco runs fine, but will be collecting dust since I cannot sell it this way.

You show the damgage- got some photos of the decoder installed on the frame  assy?

[FEC]

@woodone already removed the decoder and put in the DC board.