Kato P42 lurching problem

[ryan_wilkerson]

So my sons have been wanting to run their P42s (each of them have one) at the train show this weekend. I purchased a pair of TCS K0D8-A decoders and installed them last night. One of them runs very smoothly. The other, ATMK 123, has a lurching problem. I've cleaned the tracks and the wheels. Then I inspected the brass pickup strips to make sure they are making contact. I also soldered the motor leads on to the pads to make sure those weren't loose.

The behavior is this....
Give it some throttle and it starts off, picking up speed and after about 2 seconds, it loses power. The LED is off and then a half second later, the LED comes on and the motor picks up speed for another second or two and then cuts out again, repeating the behavior. What am I missing here? Have any advice for me?
Thank you for your help!
-Ryan

[peteski]

If both the motor and headlight go out than the most likely problem is intermittent contact somewhere between the rail and the decoder.  If you think the wheels, axle-bearing cups and the brass pickup strips are clean then maybe the decoder is not contacting the pickup strips very well. I never liked the way this setup is designed (the decoder, held by the small plastic snap, is pressed against the bumps on the pickup strips).  Doesn't seem very reliable to me.

Take the shell off and press down on the decoder (above the area where the motor sits) while the loco runs slowly and see if the problem goes away.

[ryan_wilkerson]

Thanks for the advice Peteski. I'll give that a try tomorrow and let you know what I find. If pressing down does help, maybe a drop of solder on the brass strip would help make better contact with the decoder?

[davefoxx]

Ryan,

I believe that the Kato F40PH has a similar set up, and I ended up soldering the motor contacts to the decoder pads to stop some really weird behavior on the part of the locomotive after decoderizing.   Problem solved.

DFF

[ryan_wilkerson]

Hi Dave,
I actually did solder the motor leads to the decoder pads. I'm wondering if I should solder a wire from the pickup leads to the power pickup on the underside of the decoder to eliminate that as a possible cause. Not sure if there is space for that considering it's supposed to lay flat against each other.

[peteski]

Hi Dave,
I actually did solder the motor leads to the decoder pads. I'm wondering if I should solder a wire from the pickup leads to the power pickup on the underside of the decoder to eliminate that as a possible cause. Not sure if there is space for that considering it's supposed to lay flat against each other.

Soldering motor contacts is a good idea but f the headlights were going out too then the motor contacts are not the issue.

Did you try what I asked?  What was the result?   There is no need to solder wires underneath the decoder.  Take a photo of the top (overhead) view of the chassis (with shell removed but with the decoder still installed) and post it here. I'll show you where to solder the wires.

[ryan_wilkerson]

Peteski, as you mentioned cleaning the wheels, axle cups and brass pickup strips, I started there. The wheels looked clean but I wanted to make sure so I remove them. There was some black in the axle cups so I thoroughly cleaned those. Since I had them out and the train show starts Saturday, I popped in a new set of Kato wheels. I put everything back together and it's smooth running! Issue resolved. I think it was cleaning the axle cups. I will be reusing the Kato wheels for an older Kato but will make sure they weren't the cause for poor pickup.

Thanks everyone for your input and advice! My son had a big smile on his face when he ran it today and I'm sure he'll have a great time running it at the GTS train show in Sacramento this weekend.
-Ryan

[peteski]

Good to know that you got it fixed - thanks for the follow up.

Funny that you mentioned the wheels. Friend of mine kept on saying that his P42's wheels get dirty more often than all of his other Kato locos.  We just recently replaced the wheels on one of his P42 with the new Kato wheels.  He hasn't yet had enough run on it to verify if that made the difference (whether the wheels stay cleaner longer).

[ryan_wilkerson]

Maybe it's because passenger trains have a higher operating speed and rack up more miles! I wonder how it might compare to other 4 axle Kato power...F40PH, MP36PH, F units, etc...