Looking for advice......

Hello all. I’m new to O scale and have gone the route of setting up for 2 rail operation. I have a few locos (all MTH) that I have been test running on a small oval that I have laying down at the moment.

The problem I’m experiencing comes from the following. I’m running a Z1000 brick, hooked to the accessory MTH controller (sorry, I don’t have the p/n) that has the horn/bell/direction buttons next to the throttle adjuster.

I picked up a sick, 2 rail, MTH Dash 8 for a good price, knowing that it was not operational. For giggles, I set it on the rails and slowly initiated power, to witness what the loco was doing. As voltage increased the Z1000 brick hummed, I had no lights or function on the loco,  and the breaker tripped.

Knowing that I did not plan on repairing the loco, intending to create a dummy unit, I removed the shell and completely removed all internals, motors, disconnected all wiring leads, plug-ins, switches, etc....removed the entire harness, and reassembled. I then set it down on the rails, coupled to a brand new MTH SD70 loco and, much to my surprise, I received the indentical result....humming power brick, circuit breaker trip.

I removed both from the track, put the SD back on the rails, and it performed as intended. I’m lost, as to what is the issue with having this Dash 8 on the rails with no power draw ? The unit DOES have scale wheels installed, and no cars lashed up in the scenario, so I’m stumped at what could be going on.

Any help or input is greatly appreciated.

My worst day of model railroading will ALWAYS surpass my best day at work.

Original Post

Hi Nu2OScale,

Sounds like one or more of the scale wheels is installed different than the rest and this will create a short circuit within the truck itself regardless of any other wiring.  Check to make sure that the insulated side of each wheelset  (the side of the wheelset with the nylon bushing between the axle and the wheel) are all installed on the same side of the loco.  

Scott

Thank you Scott, I’ll take a look at that and see what I might have going on.

I understand that the 2 rail system has to have an isolation feature (I’m also converting a bunch of 3 rail freight to 2 rail trucks and Kadee couplers) and that’s what has me stumped......if there were hi-rail wheels on it, I would have immediately thought of short through the axles.

I‘ll  post my findings after investigating.

My worst day of model railroading will ALWAYS surpass my best day at work.

Finding shorts can unfortunately be hard sometimes and is often a process of elimination.  As mentioned by Scott, making sure all the wheelsets are installed correctly is a good place to start.  Sometimes using two alligator clips hooked up to your power source (and touching one wheel on each side) can help narrow things down.  Or putting the engine on the track and putting a piece of paper under one of the trucks (or even individual wheels) can help narrow things down.  Other things to look for is there anything touching a wheel (like a brake shoe) that should not be touching it.  

My interpretatiion of what @Scott Kay was trying to relate to you is that in an individual wheel-axle-wheel, one wheel is isolated from the axle, but the opposite wheel is not isolated from the axle. Thus if in one truck, one wheel-axle-wheel is in stalled with the isolated wheel to the right side of the truck, and another wheel-axle-wheel in the same truck is installed with the isolated wheel to the left side of the truck, a short is created between the two rails by the connection of non-isolated wheel to its axle - to metal truck - to non-isolated wheel of other wheel set. 

 

Yeah.

Also, the insulated wheel can touch the side frame or a brake shoe . . . Or in isolated cases an insulating bushing can have a steel filing across it, ultimately resulting in a carbon track.

Once you find the short, you can re - assemble and have another powered unit for cheap!

A bunch of great ideas, thank you everyone. I will not have a chance to tinker on it today, but likely will tomorrow.

Based on the information being shared I’m getting the feeling that a malfunctioning axle/wheel isolation combo may be the culprit, as the MTH axle sets seem to have the gears and bushings manufactured on them, and only seem to mate to certain positions in the truck (I’m assuming this is the case) so they couldn’t be installed in a mis-matched configuration ? (Again, I’m assuming this is the case)

My worst day of model railroading will ALWAYS surpass my best day at work.

On Older 2 rail locos, one truck had the insulated wheels on one side, the other truck had them on the other side, and this evolved into have both trucks insulated from the chassis.   

There is problably nothing wrong with the mechanism in that loco.    There is no need to make it a dummy.   You  can  find the short and that may fix all problems and it should be simple since it is in the wheels.    Then reinstall the electronics.    If the short did not burn them up, all is good.   '

If the electronics don't work, just put in a new control board.    I don't know about MTH boards, but you can get all sorts of options for control and/or sound for DCC.     My favorite for motor control only is the NCE D408SR which can handle 4 amps continuously and has a stall rating of 10 amps.    And the motor control is just great.    Also it has 8 functions for lights  smoke (which I don't like) and any other things or lights you might want to control.

At the risk of being Captain Obvious  , and as I'm not sure what power/signal type a Z1000 puts into the track... could it be the switches on the newer loco aren't set to either 2- or 3-rail power, and DCS or DCC, whichever would be correct for the Z1000?  Might that also be dependent on whether they are PS2 or PS3 locos? 

Pete M

Frying decoders since 1994

Pete M posted:

At the risk of being Captain Obvious  , and as I'm not sure what power/signal type a Z1000 puts into the track... could it be the switches on the newer loco aren't set to either 2- or 3-rail power, and DCS or DCC, whichever would be correct for the Z1000?  Might that also be dependent on whether they are PS2 or PS3 locos? 

Lol....thanks for the recommendation Pete. There aren’t any switches or electronics in the loco, I removed them all, it’s literally just a rolling chassis now.

My worst day of model railroading will ALWAYS surpass my best day at work.

Well I didn't think that all the way through, did I?    In which case, I second the ideas about shorts caused by backwards wheel-sets or brake shoes etc. 

But at the risk of losing any last shred of credibility, I'll take one more stab at it: Could the motors (if still present) possibly have capacitors across their terminals for RF suppression?  I have a Sunset-3rd Rail non-DCC 2-rail CPR D10 which caused an increasing hum for a few seconds followed by booster shut-down when I first put it on the track. I looked all over for shorts and found none, but in the end it was caused by a capacitor across the motor.    

 

Pete M

Frying decoders since 1994

I've never had that happen to that level. However, I did get a "-2" (scale-wheel) locomotive that had the switch in the 3-rail position. This shorts the wheels together for three-rail operation as it is intended that the pickup roller be used for the hot connection.

The switches have been located in various places over various models. I believe the earlier C40-8 models (Proto-2) had the switch on the chassis, but some diesels had the switches under the radiator housing, while the GP35's have them under the dynamic brake fan housing.

If your unit is Proto 3-2 compatible (goes both ways), find the switch and check its position. If the switch is in the 2-rail position, make sure that the wheels are positioned properly as stated above. I haven't encountered a backward wheel set yet (I test them in 2-rail before putting the rollers on for use at the club). The nice thing about the 2-rail compatible MTH locomotives is that they'll run on DC with engine sounds (you won't have the horn/bell control unless you use the DCS system).

I hope this helps some.

Matt Jackson
"The best service you can provide for the hobby is to pass on what you have learned."

 Angels Gate Hi-Railers San Pedro, California

"Celebrating 20 years of moving freight and passengers from Point A to Point A!"
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Sorry for such a long delay in my follow up everyone. Turns out, Scott was on it from the start...... the scale wheel sets that I picked up (12 axles in total), were obviously a mix/match of components, and were not all from the same type of loco, as described....long story short, out of the 12 scale wheels/axles I had, only 6 of them had the appropriate insulator and gear combo make up to prevent the short. I was intitially installing the axles with gears mating to the existing idler gears (the ones between each axle), so my guess is that there may have been a 4 axle scale wheel set mixed in there with the twelve ? As some had the gear and insulator on the same side, and vice-versa.

I did hook the electronics back up, and tried it, but nothing, no lights, no hum, no anything, but it now rolls around the track behind the powered units without issue, so it’s a dummy for now.

A big thanks to everyone's input, it’s truly appreciated.

My worst day of model railroading will ALWAYS surpass my best day at work.

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