Engine stuttering in reverse

[Deleted]

So this is an interesting issue I've run up against, and I'm not sure how to solve it.

I grabbed the Athearn RTR F7A/B set last week. I ran it around a loop of track for about 1/2 an hour, forwards and backwards. I didn't notice any issues.

Last night I installed a decoder - a DH123 I had lying around, nothing special. I managed to blow the headlight circuit, but that's another story. Anyway, I installed it, and put it back on the test track. It runs fine forward, but in reverse it stutters occasionally. I tried resetting the decoder, and while I had it on a DCC loop, tried running it. It ran fine, forwards and backwards. I go back to my analog loop, and it still occasionally-  and randomly - stutters in reverse.

To recap:

On DCC, it runs fine.

On DC, it stutters but only in reverse.

The decoder's headlight function is busted, and I ordered some LED's to attach to the backup light function, but they won't be in until mid-next week, so I can't tell you what the light bulb is doing. Also, while installing the decoder, the spring and brush on the bottom of the motor popped out. I put them back in, correctly, I think, so I don't think that's an issue. But for full disclosure, it did happen.

Otherwise It's a brand new engine. Clean wheels. Mostly clean track

Anyone know why it doesn't run well backwards, but only on analog DC?

[Mark R.]

I guess my curiosity is why you went to the effort of installing a decoder, and then wonder why it doesn't run well on DC ? I've had a few "cheap" decoders that worked fine on DCC but wouldn't run well (in either direction) on DC at all.

Mark.

[Deleted]

No specific reason. I just had a circle of track setup in the living room while I was working on the conversion, and noticed the oddity. And I just happen to be anal enough to fixate on it

[Deleted]

I went through the engine top-to-bottom. There weren't any issue I could see, so I pulled the motor out of the chassis and ran it in "reverse", completely disconnected from the drive train. Same issue. I tried it with another decoder. Same issue.

I pulled out another conversion I'm working on - a Walthers Trainline Dash-8 that's currently down two couplers, and put it on the circle. Wouldn't you know, I had the same exact issue. Forward, it ran fine, but in reverse it would buck and stutter. I put the F7 on the loop, with the Dash-8 on, and ran them both at the same time. They were surprisingly speed matched . And they both performed flawlessly going forward, but as soon as I put them in reverse, they both stuttered at the same time.

I'm fairly certain that it's not 3 decoders all having the same issue, so I can only conclude it's something to do with the power supply, a late 90's Bachmann Spectrum power supply, or some way that the DH123 chip deals with analog power. I've sent Digitrax a message, so hopefully I'll get an answers soon.

[Deleted]

Digitrax got back to me (holy crap, that's a 6 hour turn around time on a Sunday!) and said its most likely due to the power supply providing pulse width power instead of smooth DC, making the decider go nuts.

Perhaps the take away is that Bachmann switched power supplies for their dcc equipped train sets for a reason. At any event, that's one mystery solved.

[Mark R.]

If it was the pulse power from the DC controller causing it, it should be happening in both directions.

To prove if it is the pack only doing this in reverse, swap the motor leads from the decoder to the motor, it should now stutter when going forward and not in reverse.

Mark.

[llxlocomotives]

I find that decoders respond properly to nearly constant DC signals. Pulse wave DC signals are a coin toss. Some seem to handle it OK others of same type decoder do not handle well. It us clear in the thread that there was something wrong with the reverse signal. The pulse is just enough different to cause confusion with the three decoders.
Larry
www.llxlocomotives.com

[wpmow]

Greenwiz, are these F7's the athearn genesis? Am having a issues with 2 installs. Both are Loksound select boards, They were in atlas GP40's and operated like a dream, took them home and downloaded the Intermountain OEM for the emd 567. Let me back up a tad ,one f7 in a intermountain the other is a Athearn F7 genesis. The Intermountain operates fine . However the Athearn run as though a wire connection is loose . Checked at Tony's exchange and there seems to be a issue with pickup,axels I believe.I will be getting replacement axels the new ones have a longer tip on the ends for better fit in the side fame are pick. While waiting I will remove truck assembleys and solder them .

[Mark R.]

While that IS a problem with the Athearn Genesis engines, the Athearn RTR engines don't have the same trucks - they are more similar to the older blue-box Athearns with the square bronze journals.

Mark.

[Deleted]

wpmow, they are the RTR variety.

At this point I'm certain it's an issue with the way that the DCC chip interacts with the DC wave for reverse running, as running a Walthers Trainline diesel I converted exhibits the same issue.

[llxlocomotives]

I find the degree of confusion that the decoder has with a pulse wave is decoder manufacturer dependent. Some are more tolls rent than others.
Larry
www.llxlocomotives.com

[steveturner]

So it runs great in DCC with decoder...............that's great and the way it should be. Why run it on DC when its meant for DCC. That's like running a gas engine on Diesel.Its a known fact you should not run DCC locos on DC because of motor issues. Stick to DCC and the issue is a non starter. Steve

[llxlocomotives]

Steve,
You have that backwards. You should not run a DC loco on DCC. It is the 30 volts total amplitude that is the problem. With a decoder, that is converted so the motor only sees 12 volts. In classic DC, no pulse wave, the decoder does not have any problem with the DC signal. Most decoders pulse the motor even in DC. like a conventional power pack. IMO a decoder on an engine is a good idea. Then your not relying on the track to send the transients. It just seems like a cleaner system to me. My testing tends to support my premise.
Larry
www.llxlocomotives.com