DCC: minor engine surging problem

[NevinW]

I have a Digitrax DCC system and I have a problem that has developed recently that I thought would be worth running by everyone and seeing what they think.

I have a pair of P2K GP7's with TCS decoders and an A-B Genesis F-7 with Digitrax that over the past couple of weeks have been doing a strange barely perceptable surging while pulling coal trains on the layout. It is like they are speeding up and slowing down continually - not much, but enough that the rest of the train occasionally notices. It follows a definite sine wave pattern. Sometimes it appears to stop. My stewart engines and my steamers are not effected and are running as smooth as can be. I cleaned the wheels and I cleaned the track to no avail. Any thoughts as to where I should look first? Check the engines for binds, switch decoders, or check power supplies? Thanks - Nevin

[dharmon]

QUOTE: Originally posted by NevinW

I have a Digitrax DCC system and I have a problem that has developed recently that I thought would be worth running by everyone and seeing what they think.

I have a pair of P2K GP7's with TCS decoders and an A-B Genesis F-7 with Digitrax that over the past couple of weeks have been doing a strange barely perceptable surging while pulling coal trains on the layout. It is like they are speeding up and slowing down continually - not much, but enough that the rest of the train occasionally notices. It follows a definite sine wave pattern. Sometimes it appears to stop. My stewart engines and my steamers are not effected and are running as smooth as can be. I cleaned the wheels and I cleaned the track to no avail. Any thoughts as to where I should look first? Check the engines for binds, switch decoders, or check power supplies? Thanks - Nevin

I'm going to preface this with "I'm not exactly sure what I'm talking about", but at our club, a member had a loco that was doing a similiar thing. Another member put it on the programming track and messed with the "dither" CV and it made it go away. I don't know what that does, or what it is, but it seemed to solve his problem. i put that out for the little that it's worth, because you may know what that is.

[Anonymous]

i have a similar problem with three of my engines. they are atlas dash 8's. on the downgrade they surge off and on. i contacted digitrax and they told me it was a mechanical problem. the worm gear at the top of the gear tower binds when the engines have pressure put on them such as going downgrade. going upgrade or on level track this is not a problem. i use a nce power system but these engines have digitrax decoders in them, installed in them at the factory. i also contaced nce and they said the same thing about the worm gears,further they said that athearn engines were notorious for this behavior,but i have three gp60m's i just bought and they run fine. i would like to hear more from others about this problem. further all my other engines kato,steward and some older atlas operate without problems

[dave9999]

Try changing CV 08 to a value of 09 (decimal). This will reset the decoder to factory settings, but will leave any speed tables that you have programmed. If this does not work
then you will have to check for loose wires. I had a P2K loco doing the same thing. Found
a wire had worked loose from the pick-up. Dave

[NevinW]

I don't think it is a mechanical worm gear problem because there are no grades on my shelf type layout. I have messed with the CV's for dither and other things on these engines. I think I will convert it back to the original settings and see what happens. - Nevin

[Anonymous]

I encountered a similar problem, only the surging was significant! The loco would suddenly take off fast (or go in reverse) for about a second.
I equipped my Bachmann 4-6-0 with a Lenz 1014 E - (european numbering, it is a silent drive decoder without back EMF speed control). The decoder just pluged into the 8-pin socket. I did not change anything, not even the lights. The loco would surge twice as fast for about a second, sometimes even reversing momentarily, also the response seemed slow i.e. it took a second to switch the headlights off. The decoder ran hot! Another 1014E did exactly the same, also getting hot; however now fitted into a P2K E7 and works perfectly and runs cool. I could not locate any bad connections etc. I observed that the Bachmann pcb had some capacitors on it though?
Any suggestions? - Alan