# Locos only running one speed- FULL trottle!



## LehmannTrains (Mar 4, 2013)

Hi All,
New to the site, but one year into large scale.
Yesterday, out of nowhere, all locomotives we tried (Bachmann big hauler, Bachmann Thomas, and AristoCraft Rodgers)
all started running at just one speed- full trottle. The controller did nothing. We tried another similar controller (both Bachmann 1-amp), different power supplies, different track clips and wires to track clips.... nothing changed. Any help would be much appreciated.... we are really scratching our heads on this one!
thanks!


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## Treeman (Jan 6, 2008)

I could understand one power pack going bad, but two would be hard to explain.


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## Garratt (Sep 15, 2012)

Divide and conquer. You have changed everything else, now change the technician. ;-)


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## Greg Elmassian (Jan 3, 2008)

Got to be a wiring issue...disconnect everything... then hook up ONE transformer to ONE track.... 

Greg


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## Scottychaos (Jan 2, 2008)

My G-gauge club had this happen at a show last year. 
two power packs in a row "died" and switched to "full power only".. 

The cause was too much amperage draw on the tracks for the powerpacks to handle..too many locomotives running at a time. 
something inside the powerpacks burned out, (a diode perhaps? I dont remember exactly) 
(I know it wasn't a fuse) 
a club member who is good with electronics was able to fix them later, but for that day, we had to take one 
of our loops out of service because we didnt have enough power packs! 

So I have seen this happen..two powerpacks burn out in the same day. 
In the case I saw, the direct result was too many locomotives on the track. 
we had two trains on one loop, each train with two USA-Trains diesels.. 
Four total diesels, Eight total motors..I dont recall the amp rating of the powerpacks, 
but they weren't "low end" packs.. 

When it first happened, with the first pack, we didnt understand the exact cause..
we didnt suspect the locomotives, because the four diesels had been running for awhile with no issues..
then suddenly, both trains sped-up to full power! we quickly turned off the power pack,
and concluded the pack was dead..but we werent sure exactly why..
"just one of those things" that can happen with older packs..

Fortunately we have a spare power pack! same model of pack..
lets just hook it up, we will have John look at the dead one later..

Trains are back running normally..about a minute later, same thing! full power!
*now* the problem was obvious! Its the trains..too many locomotives.
(track was just a simple loop) 
only logical conclusion - four diesels is too many for these particular packs.

I dont know if this is related to the Original poster's issue or not, but I 
thought I post my experience since it is a possible explanation..

Lehmann, how many locomotives were you running when this first happened?
and what is the name/type of powerpack?

Scot


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## toddalin (Jan 4, 2008)

I've had an MRC 6200 do this.

The cause is that one or some of the "transistors" (actually MOS-FETS in the 6200 I believe) short out internally. This internal short then allows the full voltage (that is normally reduced by the transistor) to be delivered to the output of the unit, and the trains go full speed. The fix is to determine which one(s) and to replace them.


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## Dwight Ennis (Jan 2, 2008)

The easiest way to check the power pack is to disconnect from the track and check the output voltage with a voltmeter - see if the voltage changes when the control knob is increased/decreased. That will tell you whether it's the pack or not.


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## Greg Elmassian (Jan 3, 2008)

Unless it is a pulse power system then some meters do indeed read full voltage all the time on pulse width modulation (solution is to put a load on the output). 

Greg


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## Dwight Ennis (Jan 2, 2008)

We tried another similar controller (both Bachmann 1-amp)These sound like pretty basic packs to me... the kind Bachmann ships with all their train sets from HO to On30 to G.


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## Greg Elmassian (Jan 3, 2008)

Ahh, you are right, he said they were indeed Bachmann 1 amper's .... yep, I'd guess that there's no PWM there ha ha! (the circuit would probably cost more than the total cost of the power pack) 

I only saw "similar" at first... 

Voltmeter it is... 

Greg


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## noelw (Jan 2, 2008)

I tried a Bachmann ho throttle and I remember that due to the var.throttle on them are wire wound tap that the pick up arm goes across to make the voltage variable. If use a digital volt meter, the first contact of the tap, it show 12 volts due to no load... So by putting a small load... maybe a car light bulb, then it became a variable voltage as I increase the speed of the throttle. Another issue can be a back feed off of another controller?

But like other said.. Sounds like something is miss wired or something shorted that makes it run wide open voltage on the D/C output. 
Just our six bits worth. We gave up the two cents worth years ago when coins was more valuable. lol


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## TonyWalsham (Jan 2, 2008)

Two Bachmann 1 amp controller failures would not be abnormal. Especially if they have been overloaded.


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## John J (Dec 29, 2007)

When I was running track power I had a fuse between the track and the controller. I would keep a good supply of the replacement fuses. You have no Idea how many times that has saved me from blowing up my controller and power pack. 


JJ


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## Jerry Barnes (Jan 2, 2008)

I had a MRC 6200 burn out on me, lost the ability to use the throttle on it. It would just put out a straight 24 volts. I used a Aristo TE for awhile, but it eventually burned out totally. So I use my Aristo 10 amp.


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## TheRoundHouseRnR (Jul 15, 2012)

My dad two Christmas ago set up his HO train under the tree just as normal. He has a very old , I think, MRC power pack. Basically built exactly like the bachmann starter set transformers. Anyway, he called me up , asking why his trains run full throttle when set on 0%, but then stop when set at 100%. As if some how the throttle got reversed . It would also run VERY hot. I stopped in to help him out.

What had happened was he wired one side of the track to AC output and the other side to the Variable DC output. I never saw this happen before but it was pretty neat. He is very knowledgeable and is a HVAC service/ maintenance tech. But in all the Christmas fuss , he just made a mistake. So this could maybe be the case. I don't know, just throwing it out there.

The Roundhouse RnR


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## LehmannTrains (Mar 4, 2013)

Thanks to all for your thorough replies. I'm going to try out some of these remedies and see what happens. 
To answer Scottychaos there was never more than one loco on the track. 
Wish me luck!


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