scorpio-50I have an atlas power pack that overnight decided to send full dc voltage (once the switch is turned on) with the speed control dial having no effect at all,whether set @ stop or full. Has anyone ever had a similar gremlin attack and any ideas for a fix. Thanks, scorpio-50
If it's a newer electronic power pack, my guess would be that the output transistor has failed and shorted "ON".
It could be easily repaired with any NPN (or possibly PNP - depends on design) power transistor or better yet, Darlington transistor like a TIP-series replacement.
scorpio-50I have an atlas power pack that overnight decided to send full dc voltage
There is a clue (failed overnight). If it's a train set pack, the potentiometer is broken. Does the action feel different than before? If it's a transistorized pack then the output transistor may be shorted.
Best solution is to replace it if you can. MRC does make decent power packs.
Karl
The mind is like a parachute. It works better when it's open. www.stremy.net
It may be even simpler than that. If it's an old pack and you're trying to run a newer engine with it, this may be a normal occurance. In the old units, the potentiometer was in series with the motor in the loco.It simply dropped the voltage across the motor by being a resistor in series that was adjustable. However, the older motors drew a lot more current, which means they were lower resistance themselves. The newer locomoties have motors that draw less current and have a higher resistance, menaing the potentiometer is now a smaller part of the total circuit resistance. The range of the potentiometer means it will vary the voltae on the motor by a much smaller amount, making it seem like it's always a full output. The above advice about getting a newer, solid state power pack as suggested above applies.
Hi!
I agree that the "pot" is likely the problem. Assuming you are not an electronics "wizard", I strongly urge you to unplug the pack from the wall socket, then cut the cord, deposit in nearest trash.
Messing with the innards can easily lead to a shock - or much worse - a fire. Having been thru both as a teenager, please learn from my experience.
Oh, for a replacement - assuming you are staying with DC - check out the MRC packs!
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
The most likely cause is failure of the potentiometer (pot). It's generally the only part that moves mechanically besides the direction switch. Cheap, failure-prone pots have been the bane of consumer electronics since I was a kid with a transistor radio.
You have to access the inside of the case to replace the pot. This may or may not be practical, depending on your experience in doing these types of tasks. Many modern power pack cases are deliberately glued (plastic) or riveted (metal) or use some other fastner designed to prevent you from opening the case. Once you gain access to the inside of the case, the pot is the piece attached to the throttle knob.
The pot will be one of 2 types - I'm not familiar enough with Atlas power packs to know which type they used. If the pot is a rheostat - no transistors or anything else besides transformer and switches - it will be relatively high power and often wire wound with a slider on the wire. Resistance will typically be around 50-90 ohms, with higher resistances being used for N scale and in more recent times. Replacements will be more difficult to locate.
A transistor throttle will use a low power pot of much higher resistance - typically 5K-10K ohms. You will want a linear taper pot for a replacement.
Reality is that it might just be easier to use the existing power pack as a fixed voltage DC power supply. Build your own tethered walk-around throttle to attach to "what once was variable DC terminals". Circuits for simple DC throttles can be found at http://home.cogeco.ca/~rpaisley4/Throttles.html and http://www.talkingelectronics.com/projects/ThrottleMkI/Throttle.html and http://www.awrr.com/throttle.html. These circuits, especially at the last link, make a great 1st electronics project. I built one to attach to an old AHM power pack that had failed in the same way yours had. Because of its walk-around capability, it became my most used throttle.
Or you could even by an MRC hand held throttle to attach to your Atlas "power supply". Make sure you connect it to the correct terminals as specified by MRC. Some of their hand-helds required an AC input, not DC.
my thoughts, your choices
Fred W
I have an atlas power pack that overnight decided to send full dc voltage (once the switch is turned on) with the speed control dial having no effect at all,whether set @ stop or full.
Has anyone ever had a similar gremlin attack and any ideas for a fix
Thanks,
scorpio-50