Rivarossi Union Pacific Big Boy DCC Problem

[Manxcat]

I am posting on behalf of a member of our club who has a problem with the DCC operation of his Rivarossi Union Pacific Big Boy purchased from a US dealer. (He's not an RMWeb member, as you have probably guessed.) At the club we have some members with good, but not expert, DCC knowledge but between us we have been unable to come up with a reason for the problem, far less the solution.

 

The loco is DCC ready and was supplied from the US with a 21-pin DCC sound decoder and a speaker wired in. When the DCC decoder is in place and the power applied, the loco stutters and jerks along the track. Immediately the power is turned off the loco then starts to move properly and glides slowly to a halt from the full speed which had been previously set by the controller. This is the case whether it is set to drive forward or in reverse. All the sounds work perfectly. We have tried a number of different DCC controllers and the loco always reacts in the same way. My ESU controller recognised the chip, via Railcom I think, and all functions seemed to work.

 

When the DCC decoder is removed and replaced by the blanking plate it runs perfectly on DC in both directions, so there appears to be no mechanical problem with the motion.

 

I put the decoder on my ESU test rig and the motor worked perfectly with no stuttering on power applied or upon reducing and turning off the power.

 

There is no visible problem with any of the wiring, the pick ups or the circuit board on the chassis, nor with the decoder.

 

We tried re-setting the decoder to its factory settings with the appropriate CV but this made no difference when it was put back into the loco. So we are now at a loss to understand what the problem is and how/if it can be resolved. Surprisingly, early e-mails to the vendor and Rivarossi did not elicit a response, other than one saying it is the other's problem or advising the purchase of a new chip. When our member complained more vociferously, he was sent a basic, non-sound DCC chip which, when put on my test rig, proved to be dead.

 

Any assistance anyone can offer will be much appreciated. Thanks.

 

Archie

[Adrian Wintle]

The first thing I would try is to disable any back-EMF in the decoder and see if it behaves then.

 

Adrian

[richard brown]

If it is a version 4 locosound you could try a auto tune on it I can't remember which is the cv value you need to change but it should be in the instructions

[10000]

Sorry I've no suggestions but can offer this info.

 

The ESU 21 pin with the official ESU sound project for the Big Boy does NOT require the BEMF to be turned off on recent models.  I have one and it runs fine with BEMF on although because of the lack of pickups on them they can suffer from dirty track.

[34theletterbetweenB&D]

...When the DCC decoder is in place and the power applied, the loco stutters and jerks along the track. Immediately the power is turned off the loco then starts to move properly and glides slowly to a halt from the full speed which had been previously set by the controller. This is the case whether it is set to drive forward or in reverse. All the sounds work perfectly...

That's the crucial information regarding the loco and decoder. What it tells you is that there is no real trouble with pick up or DCC command processing (and you have checked the loco as a DC unit with the decoder out of circuit to confirm that the motor is good, and the decoder off loco to confirm that it is basically OK).

 

So what you have is an unwanted interaction between something on the loco and the decoder, that produces its most noticeable effect when the loco is accelerating positively (negative acceleration appears immune). I would suspect other components in the loco electrical circuit - typically suppression components - interacting with whatever BEMF control the decoder uses. On the two occasions I have seen this type of trouble, you could actually hear that there was a crude tuned circuit as chirps and ringing sounds could be heard (you will need the onboard sound off!) with one's ear close to the loco. Removing the capacitors and inductors eliminated the problem.

[10000]

A bit more info about the loco/chip may help the experts on here.

 

Is it a factory fitted DCC sound model or an end user fitted sound chip?

 

If end user who's decoder is it? ESU manufacturer id is 151 

[Manxcat]

Gentlemen,

 

Thank you so much for all your replies. The loco was purchased with the sound decoder fitted. I don't know which make it is and will only see the chap next Sunday. I can then ascertain the manufacturer by reading the CV. We don't even know if it was factory fitted or fitted later by the American dealer who sold it.

 

We had thought about suppression and removing anything that looked like such a component but could not absolutely identify which, if any, these were. Being anxious not to do any damage we left well alone.

 

If he can make it to the club on Sunday he will bring the loco and I'll ascertain the manufacturer. I'll also photograph the circuit board on the chassis and post the photo in case it might help someone identify the capacitors and inductors for us.

 

We'll try all the suggestions, thanks, and I'll let you all know the position next Sunday or Monday.

[Nigelcliffe]

The original description says:
 

When the DCC decoder is in place and the power applied, the loco stutters and jerks along the track. Immediately the power is turned off the loco then starts to move properly and glides slowly to a halt from the full speed which had been previously set by the controller.

This is very unusual behaviour, but suggests that there is a substantial "stay alive" circuit in the loco somewhere. Otherwise, where is the power coming from to cause the loco to move when the power is turned off ?
I wonder if it has "DC" running enabled and that might be causing the fight between the DCC instructions and the stay-alive circuit (which delivers DC to the decoder).


- Nigel

[Adrian Wintle]

The original description says:

 

This is very unusual behaviour, but suggests that there is a substantial "stay alive" circuit in the loco somewhere. Otherwise, where is the power coming from to cause the loco to move when the power is turned off ?

I wonder if it has "DC" running enabled and that might be causing the fight between the DCC instructions and the stay-alive circuit (which delivers DC to the decoder).

 

 

- Nigel

 

I took 'power turned off' to mean throttle set to 0 which would mean there is still plenty of power to allow the loco to decelerate based on the CV setting.

 

Adrian

[nigcuberail]

 

When the DCC decoder is in place and the power applied, the loco stutters and jerks along the track. Immediately the power is turned off the loco then starts to move properly and glides slowly to a halt from the full speed which had been previously set by the controller. This is the case whether it is set to drive forward or in reverse.

 

Sometime ago I purchased a Rivarossi 'Big Boy', second hand but in as new condition. It was a later type, motor in the boiler, DCC ready but with an 8 pin socket.

I seem to recall at the time I received it, running on DC was OK ish, but needed all wheels and track VERY clean.

I set about fitting an ESU V4 sound decoder, but had a lot of trouble obtaining anywhere near good running with the loco in standard form.

 

The pick-up arrangement is very poor and relies on plungers IIRC. In actuality I am sure it only picks up from two driving wheels on each side (diagonally opposite driving sets)!

I stripped, cleaned, de-greased, tweaked, fettled and checked all connections to no avail.

 

The fitting of additional tender pickups on both sides transformed the performance with no stalling, intermittant acceleration, loss of sound etc..

 

Now I cannot provide any technical reason that DC performance should be better (not perfect) than DCC other than:

 

1.  The acceleration delay will keep resetting if there is poor contact, thus the loco will continue to keep starting from 0 mph and trying to accelerate until power is intermittantly lost.

2.  The current draw could be more under DCC (with sound) therefore highlighting the weakness in the standard pick-up arrangement?

 

My suggestions, for what they are worth, based purley on my experience with this model, to diagnose if it is a pick-up weakness:

 

a.  Disable accleration on the Loksound  (F4), and see if the running under DCC improves.

b.  Then, if you can, bench test with track power leads connected direct to the pick-up wires, therefore by-passing the wheel to pick-up contact process.

 

If things improve to your expectations, you know where the issue lies.

 

Of course, your later model with 21 pin socket may have improved pick-up arrangements, in which case, comletely ignore everything I have written  , other than the F4 test.

 

Good luck.

[Manxcat]

Gentlemen,

 

When I said "power turned off" I did indeed mean that the controller throttle is reduced to zero. Thanks for the additional suggestions. More for us to think about and try on Sunday.

 

Archie

[Manxcat]

Gentlemen,

 

As promised, here is a picture of the printed circuit board in my friend's Rivarossi Big Boy. I assume the orange components marked C1 and C2 are the capacitors and the two tube shaped components are the induction coils.

 

Alas folks, the solutions you all kindly suggested are now somewhat academic because of what happened in the middle of the week. My friend was more anxious to have the problem resolved than I thought and decided to take the model into a local trader. This man, according to my friend, messed about with the decoder on his test rig for close to two hours then handed everyting back with the advice that it was totally broken and no-one would be able to do anything to fix it.

 

Back at the club yesterday I tried to get it to work as it had done before. You will remember everything was fine apart from the movement problem. Yesterday we discovered it had been well and truly ruined. Every time we interrogated CV1 to get the address the trader may have changed it to, the chip reported a different, apparently random number, somewhere between 0 and 125. I'm not sure a decoder can even have CV1 set to 0. Many CVs would not return any value at all and nothing we could do would make the motor on my ESU test rig turn. The LEDs on the test rig used to show that the lights would work were all haywire and flashed intermittently then burned really bright, all with us doing nothing on the controller. We concluded the trader had well and truly bodged it.

 

No need to tell us what redress we have against the trader guys as we are well aware.

 

And thanks again to everyone who was so helpful. I am not a prolific poster on RMWeb but I read it a lot and it never fails to amaze me how tolerant, understanding and knowledgeable people here can be.

 

Archie

[melmerby]

As a last resort you could try a hard reset. (Nothing to lose I suspect)

 

Try writing 8 into CV8 (It's read only but doing that will reset it to factory settings in many decoders)

 

Other values possible here: http://tonystrains.com/technews/dec_rescue.htm

 

It maybe the jerk that messed with it has set some CV's to some incompatible values.

 

Keith