# Need help with my MRC Tech 2 2500



## Green River (Dec 19, 2009)

I stumbled across one at the flea market thought it would make a good replacement for my old gold box Tyco. When I plug it in and flip the power on switch the loco immediately starts humming like it has just a bit of power, as I turn the knob the power does increase and the loco starts to run as normal but when I come to a stop the loco just hums like it has not turned completely off. Is this normal for this transformer? it also has "braking" and "momentum" what are these features? I tried this transformer with an older yellow box Atlas and an Athearn RTR with the same results.


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## DonR (Oct 18, 2012)

My first thought is that the power pack may be leaking AC onto the
track. AC will cause a DC motor to hum and possibly
damage it. This could be caused by a failing rectifier in
the power pack.

You might use your multimeter set to AC volts and connect
it to the output of the track terminals. You should not
get a reading. If you do the power pack is defective.

Check the track terminals also by setting the meter to DC volts.
You should get a reading from 0 to 12 or so volts. If - shows,
reverse the probes, or flip the reverse switch. 

I have never used a power pack with the braking and momentum controls
but they do modify the track current in some way and could be
the cause of the hum. You can turn off these features, however.

Don


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## tkruger (Jan 18, 2009)

I have several MRC power packs with both braking and momentum. What the momentum feature does is to simulate the required starting and stopping distance of a locomotive. When the feature is enabled power being supplied will be gradually increased to the point that you set your dial at. When you return the dial to zero the power will gradually return to zero. This is a great feature when running old locomotives that do not have flywheels to make them 'coast'.

The brake feature is just what it says it is. You hold that switch down and it cuts the power to the track as if the engineer performed an emergency stop. If you have momentum on it overrides the effects of that. Great feature when you kids drive that toy car onto your track.

The hum sounds as if there is AC being put to the track, meaning a defective pack as stated earlier. Or the voltage is not truly returning to zero. If it is putting out a small amount of DC current to the track and it is not enought to turn the morot in the loco this to is an issue. 

Both of these situations can be tested with a multi-meter. 

Another possible but rare cause could be that the house wiring is not giving clean current to the power supply. All the DC power suppply does is reduce the volts from 110 to 12 and cut the AC wave in half thus you get DC. I had an issue were the trains and a radio would not work correctly in a plug but a lamp would. This issue was that there were the proper volts at the plug but the amperage was lower than it should have been. We needed to replace a breaker and take a few items off of that circuit to correct the issue. This is very unlikely though in your case.


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## Green River (Dec 19, 2009)

I checked the voltage, getting 1.8 volts DC and 0 volts AC. I tried to open the case but it has some of those Tom-foolery fasteners, they look like small torx head with the pin in the center  not sure where I can get a tool for that.


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## CTValleyRR (Jul 26, 2014)

What is the rheostat (control knob) setting when you're getting 1.8vDC? If it's at zero, there should be no voltage going to the track. 1.8v is probably enough to make the motor hum, but not enough to actually get the loco to move.

The fix may be very simple: try removing the control knob and see if you can eliminate the stray voltage by turning the shaft with a pair of pliers. If so, see if you can re-install the knob to allow the rheostat to be set all the way to zero.

Sounds too easy, but I had it happen with a cheapo Atlas controller.


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## Howard1975 (Jan 6, 2014)

CTValleyRR said:


> What is the rheostat (control knob) setting when you're getting 1.8vDC? If it's at zero, there should be no voltage going to the track. 1.8v is probably enough to make the motor hum, but not enough to actually get the loco to move.
> 
> The fix may be very simple: try removing the control knob and see if you can eliminate the stray voltage by turning the shaft with a pair of pliers. If so, see if you can re-install the knob to allow the rheostat to be set all the way to zero.
> 
> Sounds too easy, but I had it happen with a cheapo Atlas controller.




I second that advice, take off the control knob, turn the shaft to zero, and see if that eliminates the hum.

By the way, I have two of those MRC Tech 2 2500 power packs, which I bought used many years ago, and both of mine still work perfectly.


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## Green River (Dec 19, 2009)

The knob is on zero when I get the 1.8 volts DC even with the knob removed, the stopper is in the rheostat. I also ordered the proper tools to take the case apart, the whole set was only 6 bucks. There is a guy that I work with that is an electronic guru so I asked him about it, he said that rheostat should have a thin plastic strip that separates the wiper from the board when the knob is on zero to completely shut off the voltage and that the 1.8 volt is normal if the plastic strip were missing, he even pulled up a picture on the internet and showed me what he was talking about. I should have my tools in a couple days and we will find out for sure, maybe we can all learn something from this.


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## CTValleyRR (Jul 26, 2014)

Sounds like something you can fix with a small piece of thin styrene. Keeping my fingers crossed for you!


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## Viperjim1 (Mar 19, 2015)

You can get a set of security torn bits at Home Depot or harbor freight for about 8.00 from small to larger than you'll need


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