Aristocraft DC power supply and controller 5450, 5401 DEAD?

[TeddyB]

Hi ALL!

I have this 2 part power supply from Aristo-Craft its for G scale. The DC power supply works puts out 20 V, dc ( I have a meter). Then you attach the supply to the controller...it doesn't seem to work. It puts out the same 20 VDC, ALL the time. The knob has no effect. When you use the switch that changes direction or stop, that does work, it does stop when you put it in the middle. It does change voltage polarity, or direction when you move the switch. IS IT DEAD? That controll knob has no effect, is there some sort of reset inside?

Many thanks, Ted

[ATLANTIC CENTRAL]

Ted,

The controller is a solid state transitorized speed control.

Have you actually tried to run a train or only tested it with a meter?

Is it a digital meter or analog meter?

If you have tried to run a train, but have no spped control, the throttle portion is damaged and needs repair or replacement. Aristo Craft may be able to fix it for you.

If you have only tested it with a digital meter, I suggest you try running a train before you assume you have a problem.

Digital meters often to not introduce enough resistance into some types of transistor throttle circuits to actually allow them to work correctly. You may be reading voltage, but no current is available that would make a motor turn, this is how some of these circuits work. An analog meter would likely work better, but still may not give you an accurate voltage reading without having a suitable motor load in the circuit.

Sheldon

[rrinker]

 Well actually it's that they introduce too much resistence - 1 MOhm or better for a decent quality meter. The idea being to NOT load down the circuit under test.

 Otherwise, yes, test it with a train. Depending on the design of the actual throttle circuit, the load of the locomotive motor may be a critical part of the circuit, and when tested with an open circuit it will show the maximum voltage at all times. If you don't have a train to test it with, a couple of auto taillamp bulbs should put enough of a load on it to work, although at maximum throttle you will exceed the bulb's rating  so keep it to half throttle or so. The bightness should vary, and you should see a voltage difference if this is the case. Otherwise, it probably is broken.

                                   --Randy

[TeddyB]

Hi, and thanks.

This is what I'm hearing from others.

My MRC 6200 did the same thing.  It was a burned out transistor (shorted) that continually allowed 21 volts to come through regardless of the throttle setting.  The forward and reverse still worked.  I suspect the same has happened to you.  If you are handy with a soldering iron, you may be able to find a replacement and replace it yourself.  Otherwise, get hold of AristoCraft for repair.

                                     ~AND~
Look for a single device, probably a TO-220 package (3 leads, a black epoxy body and a tab with a single screw hole). Hopefully, it will have a more or less standard part number on it and you can find a suitable replacement. A shorted output FET will do just what you describe. Todd is probably correct in his assessment.