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 Posted - January 03 2010 : 10:22:39 PM
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Hello all,
In an earlier post I wrote that I was going to attempt to repair (bring back to life) a Tyco Amtrak F7 with a MU-2 mechanism. Unfortunately I have run into some snags with this project and I am wondering whether it is worth proceeding further.
First of all I have discovered that there is a short circuit somewhere inside the armature itself. I determined this by disassembling the power truck and connecting power directly to the motor brushes. I found that short appears and disappears based on the orientation of the commutator. Is this a sign that I have a broken winding in the armature or is there something else that could be causing the short?
Second, while disassembling the power truck I discovered that both plastic wheels on both trucks are cracked. The cracks on all four wheels are the same, they extend from the axle hole out to the wheel tread. Do Tyco's insulated locomotive wheels crack with age? Is it worth finding replacement wheels for this locomotive?
In the end the question is, is this Amtrak F7 salvageable or is it good only for parts? If it's only good for parts which parts are worth saving and which should be junked?
Any tips, opinions, or ideas would be greatly appreciated.....
Thanks
Scott
Proudly keeping Tyco Pluggers out of landfills since 2016
Edited by - Srenchin on January 03 2010 10:25:16 PM
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 Posted - January 03 2010 : 10:37:47 PM
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All common problems. All repairable, but the value equation of the repair is only determined by the user. You already know what a PITA these motors can be to disassemble, etc...
The armature may simply have excess carbon or other material bridging the commutator plates. Carefully clean the gaps (slots) between them with the tip of a hobby blade and try again.
As for the wheels: it's a common problem, but not necessarily a universal one. Sometimes the crack does not affect performance at all, and the motor truck should have traction tires which would lessen the symptoms even more. If the flanges are intact, run it.
If you can't get the motor to run (because your armature is shot), then trash the whole thing... it would be easiest to swap a whole new truck in place. Maybe save the metal wheels, brushes, and axle gears and truck sideframes for future repairs. Especially the sideframes... I've found countless otherwise perfect examples with missing ones.
MU-2 locos are a "dime a dozen" if you look in the right places... look for Santa Fe and Burlington Route units as these go wanting the most often, and don't forget about the GP20.
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Posted - January 04 2010 : 11:23:31 AM
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When is a malfunctioning Tyco MU-2 a lost cause?
never, Ray Marinaccio would just put a big block chevy under the shell.
jerry
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Posted - January 04 2010 : 11:42:44 AM
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Tony,
Thanks for the info about these mechanisms, especially the tip on cleaning out the gaps between the commutator plates. Alas the motor still insists on shorting out.
Is there a way of telling if an armature is burned out simply by a visual inspection or is this something that can be done only by running electricity through the windings?
Speaking of which, what exactly happens when an electrical motor burns out? I know smoke pours out of a motor in trouble, but where exactly is the smoke coming from? Are the copper wires in the armature actually catching fire and melting, or is it something less dramatic?
Scott
Proudly keeping Tyco Pluggers out of landfills since 2016
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 Posted - January 04 2010 : 6:53:21 PM
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Dear Tony,
I took your advice and junked the original MU-2 drive for my Amtrak F7. The good news is that I was able to salvage a serviceable drive from a beat up Penn Central F7 that I found in the "parts box" at my local hobby shop. I can't say that its the smoothest runner I have seen, I could not find adequate replacement screws for the rivets at my local hardware store so I could not disassemble the Penn Central's drive to give the mechanism a good cleaning and lubrication. However I did what I could and now the Amtrak F7 is in operable condition.
Thank you again for your help....
Scott
Proudly keeping Tyco Pluggers out of landfills since 2016
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Posted - January 09 2010 : 4:59:22 PM
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Scott, what you described is the classic symptom of a shorted armature. The motor can usually be kick-started if spun by hand, but it draws a high current and stalls easily when shorted winding comes into play.
If you want to give the new motor a good cleaning, blast it out with contact cleaner from Radio Shack. Be sure to get the plastic compatible stuff.
The Tyco Depot
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Posted - March 28 2010 : 6:11:00 PM
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quote:Tony,
Is there a way of telling if an armature is burned out simply by a visual inspection or is this something that can be done only by running electricity through the windings?
Speaking of which, what exactly happens when an electrical motor burns out? I know smoke pours out of a motor in trouble, but where exactly is the smoke coming from? Are the copper wires in the armature actually catching fire and melting, or is it something less dramatic?
Scott
Originally posted by Srenchin - January 04 2010 : 11:42:44 AM
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( From an Electronic Technician's experience : )
The smoke is generally from the insulation burning off the wire because it's so hot, either the plastic insulation, or in case of armature windings, the lacquer finish. It's not the metal itself.
To tell electrically (without power ) if an armature winding is shorted, you need what is called a Multi-meter, or Ohmmeter, to check the windings. This gets into specialized diagnostics, you would need to test each arm winding and check it to ground. And because the wire winding ohms ( resistance ) is near zero, it would look like a short to any cheap ohmmeter as well. There are specialized ohmmeters that are made to be super-sensitive to resistance, for checking windings like this, but you won't find them at retail stores, and they cost hundreds of dollars. Usually if they short, they burn thru the insulation, and short to the armature arm they're wound around, which is metal of course. So test directly from a wire joint to the bare metal of each arm, and there shouldn't be any short, if there is, that's the arm that has the bad winding on it. Of course test them all to be sure. You can buy cheap ohmmeters at flea market vendors for $5-10, they can be useful for simple electrical diagnostics, just not as accurate. Here you just are looking for a direct short, not a few ohms difference in reading, so they'll do fine. Even most auto parts stores carry cheap Ohmmeters now. If you don't have one, get one, they're invaluable for testing 90% of common model railroading problems. Good luck!
Jerry
Electronic Test Tech, 30+ years
" When life throws you bananas...it's easy to slip up"
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