# Issue about MRC Tech II Loco motion 2500



## silverfank (Sep 15, 2021)

Hello everyone,
I just received the item from ebay. the issue is that although control is set zero, voltage is still run from control as picture below.
The model looks very like new, still got warranty sticker on its back.
Has anyone had this model and the same issue as me?


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## Old_Hobo (Feb 20, 2014)

Mine does that too…..yours may look new, but mine is almost 30 years old….

And that is not a warrantee sticker….Its a security label….


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## mesenteria (Oct 29, 2015)

I agree with the above, but I honestly have never measured the posts on my MRC simple DC controller of 20 years ago. But, when I zero the knob, the lights don't even glow a bit on my On30 locomotive, and it certainly doesn't indicate it needs to move a bit. That sticker is not covering a seam, that I can see, so it will not be torn when someone attempts to disassemble the item.

I will keep reading here to find out if it's common for some bleed-over voltage to show at the posts of DC controllers when their knobs are set to 'zero' voltage.


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## T-Man (May 16, 2008)

I checked two old models I have. One was zero the other was .02.


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## wvgca (Jan 21, 2013)

it should be checked attached to some track ..... even though there is some voltage showing, the current is very minimal ....
hooking it up to a bit of track with a loco on it will actually show you if there is anything -important-- coming out when the knob is a zero position


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## Old_Hobo (Feb 20, 2014)

That’s how I noticed mine does that…..a loco on the track moves ever so slightly when set to zero….


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## rrman987 (Aug 29, 2021)

Old_Hobo said:


> That’s how I noticed mine does that…..a loco on the track moves ever so slightly when set to zero….


I _WAS_ going to suggest that you needed to load down the output (light bulbs or engine) so electronics have something to work against. However in this case I would suspect an output transistor or triac is "leaky" allowing some voltage through or isn't being driven hard enough to keep the output at 0.0V. Probably see if seller will take back or if MRC will repair, though MRC cost (plus both way shipping and wait time) may almost equal brand new warranted unit. You could then repurpose "bad one" to light structures or lights.


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## Old_Hobo (Feb 20, 2014)

My unit is almost 30 years old, so warrantee has long ran out….so I will live with it, until/unless someone comes up with a solution…..


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## kilowatt62 (Aug 18, 2019)

I have five of this particular model. Heh, yes 5. “It was all about that momentum switch for me back then.”
A few years ago, I noticed this very same issue with one. So I tested all 5 and found 2 to read about .4 & .6v, a 3rd read just over a volt. The other thing I noticed was a very mild voltage fluctuation at a given setting without a load on a couple of them. Issue there? I don’t know enough to give an opinion. So, I Called my electronics guru. His reply was pretty much the same as what rrman987 said. “Probably leaky ouput transistors.”
“If it gets worse, bring em in for bench testing here.
So I guess this is a common thing for these old tech II series controllers. I have read other comments/questions about them in the past.
Personally, I’m not concerned with a 1/2 volt since they are used to run 40 to 60+ yr old open frame dc71 and the like type motors.
The one reading over a volt has been relegated to accessory duty just because.

I say, if you got it cheap enough and you're concerned about that 1.27v but still want to keep it then, find a local electronics guy and bring him the unit with the back cover removed. You’ll need a long, slim shank #10 security torx screw driver for that.

Scott


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## MichaelE (Mar 7, 2018)

Here is a forum thread on another forum about this problem and how, in one example, it was solved.

This may or may not solve the problem, but the symptoms are the same as your problem and many other owners.

MRC Tech II 2500 problem - Model Railroader Magazine - Model Railroading, Model Trains, Reviews, Track Plans, and Forums

This thread illustrates a disassembled power pack with a photo of the circuit board and the Darlington transistor that may be leaking. It would appear from reading through this thread that replacement of the transistor is the easy part; getting at it could prove to be a bit of a challenge.

MRC DC throttle -zero setting "drift" - Model Railroader Magazine - Model Railroading, Model Trains, Reviews, Track Plans, and Forums


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## T-Man (May 16, 2008)

The number 10 security torx bit is the key. You must have a driver not just a bit. The access is too small and deep to remove the torx screw by using a socket and extension.

The time I opened one up all I had to do was replace a diode. It was in half and easy to find.


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## kilowatt62 (Aug 18, 2019)

T-Man said:


> The number 10 security torx bit is the key. You must have a driver not just a bit. The access is too small and deep to remove the torx screw by using a socket and extension.
> 
> Absolutely agreed T-man.
> I tried everything I own in that realm of tools. Nadda!
> ...


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## silverfank (Sep 15, 2021)

Hello everyone,
here is the video showing its problem. It causes humming noise from locomotive. I have 4 locomotives, the same problem is occured to them.




The issue is not occured with my Kato control, although setting throttle to the same dc current about 1.27 dc volt.


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## kilowatt62 (Aug 18, 2019)

silverfank said:


> Hello everyone,
> here is the video showing its problem. It causes humming noise from locomotive. I have 4 locomotives, the same problem is occured to them.
> 
> 
> ...


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## T-Man (May 16, 2008)

A diode will reduce voltage by .7 volts. Two diodes in series will fix the symptom with another two to handle reverse current. 5 amp range will suffice for operation. Just a shorter version of the O Gage horn button. It will buzz again if the voltage increases above 1.4 volts. The Triac is the problem.


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## rrman987 (Aug 29, 2021)

If the MRC uses a bridge diode configuration (do not know how MRC designed this DC supply), I would suspect maybe a bad diode that is (partially) shorted so you don't have pure DC but AC leaking through. Pushing the brake is just turning off the output so humming fades away as I watch the video. Corrections welcomed.


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## silverfank (Sep 15, 2021)

rrman987 said:


> If the MRC uses a bridge diode configuration (do not know how MRC designed this DC supply), I would suspect maybe a bad diode that is (partially) shorted so you don't have pure DC but AC leaking through. Pushing the brake is just turning off the output so humming fades away as I watch the video. Corrections welcomed.


There are 2 dc outputs from this model, leftone is fixed 17 dc and right one is variable.
I have no idea if multimeter AC mode can measure DC output. This is the result when AC mode measure on both DC outputs.

Output from fixed DC.










Output from variable dc.


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## silverfank (Sep 15, 2021)

Hello everyone,
I have already given up on this model, bought a second one from Ebay, shipping cost is expensive than item price as well.
I still got the same symtom as the first one, AC current leaking from DC output but less than the first one. I don't know if it is typical for this model. But for me, i don't want to risk my engine with it. control vibrates my engine all the time, even though setting throttle to zero.


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## rrman987 (Aug 29, 2021)

What you are seeing and measuring is the AC ripple on top of the DC output hence the engine humming and vibration. If this were my unit, I would open it (note: requires special long shafted headed drivers for their tamper proof screw heads), trace out circuit and put as large value filter 35V or higher capacitor that will fit inside case and connect it to the output of the bridge rectifier, NOT the track output (since its polarity is reversible and will immediately damage capacitor and pop output transistor(s)). That SHOULD clean up the AC "noise" and make train run quieter. If you still see some DC output leakage at zero throttle, add a small 14-16V incandescent lamp across the track output which should pull the output to near zero voltage.


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## CTValleyRR (Jul 26, 2014)

Well, MRC gave up on that model long before you did. It's very retro.


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