Kato P42 DCC Problems

[jmarley76]

I have two N scale Kato P42's, both with Digitrax decoders, that I have had for some time. I have a real love/hate relationship with them as sometime they work, more often they don't. I purchased both used from eBay, and they worked fine with their stock DC board in.

It seems like they have a short of some kind. They will usually run just fine with the shell off, and sometimes applying gentle pressure on the center of the decoder will make them go. Usually, if I can get them to run a few laps, the will continue to work just fine. I'm not sure entirely what the problem is or if this is a more common issue or symptom of something else? Any help would be greatly appreciated!

[peteski]

It is most likely intermittent connection (open), not a short.  I hate the way Kato designed these locos as far as electrical contact goes.  Especially the way the motor leads are held over the decoder contact with the silly plastic snap.

I am planning on writing an article on how to make these installs reliable.  Basically I re-route the motor contact strips to the inside of the chassis (not to go around outside of the truck pickup strips, and then solder short jumpers between the decoder and the truck pickup strips.  Once this is done, the model never has problems again.

There are other Kato modesl which share this design and the fix applies to all those models.

I'll post some more details later.  There is hope!   

[eja]

I threw away the plastic thingy and soldered the contacts.  No more problems.

eja

[jmarley76]

It is most likely intermittent connection (open), not a short.  I hate the way Kato designed these locos as far as electrical contact goes.  Especially the way the motor leads are held over the decoder contact with the silly plastic snap.

I am planning on writing an article on how to make these installs reliable.  Basically I re-route the motor contact strips to the inside of the chassis (not to go around outside of the truck pickup strips, and then solder short jumpers between the decoder and the truck pickup strips.  Once this is done, the model never has problems again.

There are other Kato modesl which share this design and the fix applies to all those models.

I'll post some more details later.  There is hope!   

I look forward to reading it! 

[jmarley76]

I threw away the plastic thingy and soldered the contacts.  No more problems.

eja

I thought about that, I'll have to build up my courage to solder on a decoder... 

[peteski]

I would not get rid of the plastic snap - it keeps the decoder from dislodging from the plastic tab in the rear hole, and it also provides pressure for more positive contact with the side pickup strips.

I took some photos of my installs earlier today - I'll try to do a write-up tomorrow.

[Wutter]

Intermittent connection between the pickup strips and the decoder is usually the main problem I've had with this type of decoder. After doing the Kapton tape where the motor leads come up, I usually reinstall as before, making sure the back of the decoder is actually sitting under the rear clip, as well as replace the front motor tabs clip. Then I will solder the motor tabs to the decoder. In the worst case scenarios I have also needed to solder on a jumper from each pickup strip to the pickups under the decoder to ensure reliable contact.

[peteski]

As it has been mentioned already, the most likely problem is intermittent contact either between the side pickup strips and the bottom of the decoder or between the motor contacts and the decoder. In my view this is not the best design, but we have to put up with it.

You could determine which of the sets of contacts is intermittent. If the loco doesn't run but you can still control the headlights then the motor contacts are acting up. If everything is dead (headlights and motor) then the pickup contact strips connection is flaky.

There are at least 2 versions of Digitrax DN163K0 decoder and a TCS version.  Their motor contacts are slightly different, so I have two different methods of installing them.

The newest revision of the Digitrax DN163K0 decoder has motor contact pads on both sides of the circuit board.  As shown in this photo of the bottom of the decoder, those pads are smaller then the ones on top.  Those pads are gold plated - that is good for reliable contact.


DN163K0_906.jpg

When installing those decoders I first totally remove the motor and reshape the contacts like this.


DN163K0_904.jpg

Then carefully reinstall the motor back in the cradle threading the contacts through couple of slots which seems like Kato made just for this purpose!  Then I bend and trim the contacts as shown in the photo. The length is critical: if they are left too long or too short, they won't make a solid contact with the decoder's motor pads.  Then bend them as shown in the photo.  This way when the decoder is installed and the motor contacts arepushed down by the decoder, the peak on the strips will contact roughtly at the center of the decoder's pads.


DN163K0_905.jpg

At this point, reinstall the motor in its cradle back into the metal chassis, install the decoder and snap in the plastic snap.

The other decoder type requires another installation method.

DN163K0_901.jpg

First of all, DO NO USE Kapton tape!  I hate using that stuff in this installation, just as much as I hate using duct tape on anything!    The tape adds thickens to the pickup strips, affecting how they contacts the bottom pads of the decoder, plus I don't trust it to keep the contacts separated. I know, it works, but still dont' like it.

With the circuit board removed take a fine-point black Sharpie marker (pencil will also do the job) and mark on the pickup strips areas around the motor contacts.  Make the mark wide enough to make sure the motor contacts will not contact the pickup strips. Then take the pickup strips out and using a cutoff wheel in a Dremel tool grind the marked notch in the pickup strips as shown here.

DN163K0_900.jpg

The way I grind the notches is by holding the pickup strip in a pair of small vice grips.  I just grab the strip directly under where the notch will be (yes, there is not much metal to hold onto, but I have no problems), then I use a cutoff wheel running at a medium-to-slow speed in a Dremel to grind out the notch.

Then install the decoder and bend the motor contacts as shown here.  The bend will create a more positive contact after the gray T-shaped snap is installed.  Alternately, these contact can be shortened and soldered to the pads.  I recommend using solder sparingly and making the solder joints close to the outside edges of the decoder (so the solder does not interfere with the T-shaped snap).


DN163K0_902.jpg

Install the plastic snap and you should be good to go.

If the pickup strips are still intermittent then like Wutter said, you could solder wire jumpers between the decoder and the strips.  This picture shows where to install the jumper wires (purple) on this particular decoder (the other two decoders might be different, but I don't have them handy to show).

A tip when soldering the wire to the pickup strips: When they are still out of the model, pre-tin the areas where the wire will be soldered (you can mark the spot with a sharpie marker when the light board or decoders is still assembled).  Those are shown as blue areas on the strips.  Then, while still not installed in the model,  solder ends of each jumper wire to each pre-tinned area.  That eliminates the possibility of melting the gray plastic cradle if the wires were soldered after the installation. Once the pickup strips and the decoder are installed, solder the other ends of the wires to the appropriate spots on the top of the decoder.

(Ignore the red, gray, and blue wires - those are for the ditch ligts.)

DN163K0_903.jpg

[bman]

I soldered the contacts on a friends P42's as well. Problem solved. 

[trainforfun]

I threw away the plastic thingy and soldered the contacts.  No more problems.

eja

I did that too , just hold the brass clips to the board with a small screwdriver with your third hand while you solder it . 
No more problem !

[mmyers]

I tin the two motor contacts and the two pads on the decoder. Now hold a contact down on the pad with a pin  or small jeweler's screwdriver. Heat the contact, solder flows. Memove heat and hold a few seconds until cool. repeat with other tab. Your choice whether to reinstall the plastic clip. I do so that it doesn't get lost.
I have about 2 dozen P42's, E8's, PA's, F40PH, and F units. Every one of them had stalling issues due to poor motor contact. I tried arcing the contacts, shimming, you name it. Soldering cured the issue. To remove the decoder simply touch a soldering iron to the contact. It will separate when hot enough.  It took me much longer to type this then it takes to solder those two contacts.

Martin Myers

[jmarley76]

You guys are making it sound easier then I want to believe... I will just have to jump in head first then! 

[jmarley76]

Finally got around to getting enough courage to take the soldering iron to a decoder. I must say, the results are great, no more issues what so ever! Since I got one fixed, I'll work on the second... maybe a photo to go with... 

[gkoproske]

I have umpteen Kato P42's, and when decoderized they work first time every time.  Make sure the Kapton tape is wrapped around the contact strip in the proper direction.  There can be greasy black stuff accumulated on the underside of the contact strips where the nub from the trucks touches.