yesterday i installed a dh123 in an athearn gp40-2 i had it running fine for a bit ,but the next time i started my dcc system up it started to run withouth command and i eliminated any possible source for a short circuit however the problem persists . does anyone have any ideas what the problem maybe and how i can fix it?
Did you turn the throttle down to 0 speed before turning your system off? If you didn't, the decoder may still set to run at the speed step it was set on when you shut down.
What DCC system are you running?
Did you set CV29 to 34?
What that does is turn set to long address, forward motion and DC mode off.
Sometimes decoders will think they are on a DC track and switch to DC mode. When this happens the loco will take off on it's own. Turning off DC mode fixes this.
The other common item is as cacole noted. A throttle that isn't turned all the way down or even a second throttle on the layout.
Springfield PA
im using the nce powercab
Hamltnblue Sometimes decoders will think they are on a DC track and switch to DC mode. When this happens the loco will take off on it's own. Turning off DC mode fixes this.
If a decoder thinks it's on a DC track when, in fact, it is on an AC DCC track it will just sit there and buzz, it will not "take off" any more than a DC only engine would just take off and run.
I would be more inclined to think that it is still assigned to a throttle and the last command was not "0" speed.
Dave
Lackawanna Route of the Phoebe Snow
Your problem is most likely CV29. Set it to 34 and give it a try.
Even if you don't have a problem with loco's taking off you should turn off DC mode, unless using it on a DC layout.
I learned the hard way. One day when I was starting out in DCC an AC6000 took off full speed and ramed another train. When it happens the affected train usually doen't respond to the throttle.
the speed was set to 0 and changing the cv to 34 did not seem to do anything
it looks like all cvs are automatically changing back to a setting of 255 even after i attempt to reset them
Phoebe Vet Hamltnblue: Sometimes decoders will think they are on a DC track and switch to DC mode. When this happens the loco will take off on it's own. Turning off DC mode fixes this. If a decoder thinks it's on a DC track when, in fact, it is on an AC DCC track it will just sit there and buzz, it will not "take off" any more than a DC only engine would just take off and run. I would be more inclined to think that it is still assigned to a throttle and the last command was not "0" speed.
Hamltnblue: Sometimes decoders will think they are on a DC track and switch to DC mode. When this happens the loco will take off on it's own. Turning off DC mode fixes this.
Actually it doesn't. The decoder still puts DC to the motor but it's usually at max throttle. We see this come up now and then and is very common. I've seen it at the club several times as well.
Try resetting the decoder by setting CV8 to 8.
After you figure it out you still should set cv29.
i did try but beforei could the decoder quit working i will try a new decoder i think i have a spare lyin around somewhere
It could be the decoder but it's not common. If reset and CV29 didnt' fix it then I'd try another.
With a throttle off zero the decoder reset would put it back to 3 and it would stop at that point since the address would have been to the long address.
Hey phoebe, on the right hand side of the screen half way down type DC MODE in the search our community box. You'll find plenty of hits on the problem I'm referring to.
thanks for the help everyone
All CVs reading back as 255 means the decoder is never acknowledging any actual value. The motor outputs could eb blown which may indeed make it take off at full speed.
The question is, what killedit? If the motor is not properly isolated, or a track pickup wire came into contact with one of the motor leads in anyw ay, that's often instant death to a decoder. Carefully check before just plugging in a new decoder. Something made the original one fail.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy is correct on this one. Usually you will get CAN NOT READ CV on the power cab screen but sometimes you will see 255 or a value that has nothing to do with the CV at all. Find out why the decoder got toasted before plugging in another. Another way is to rip out all the factory electronics and hard wire a nine or seven pin JST harness depending on the decoder used in it.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!