BLI Mikado short circuit ???

[Maletrain]

After getting the OEM cab off the BLI Mikado and fitting a trial version of the B&O cab, I put it on the test oval to see how the clearances work between the cab and tender.  I had not run this loco, before, it was new-in-box.  It started up and ran with sound, but before it had made a quarter lap, the sound would cut out and restart.  That happened multiple times without the loco actually stopping  Then, the loco began to stall and need a nudge to run, but would run OK, until it stalled again.  I thought the track or wheels must be dirty, so cleaned them, but the problem continued to get worse, and I notices that the stalls were actually tripping the PSXX breaker (set at 1 amp). 

After only a few laps (about 20' each), the loco would not move, and the PSXX was showing a continuous short. 

I separated the tender from the loco and determined that the short is in the loco.  At this point, if I put the loco on the track, it shows a short.  If I nudge it forward or rearward, it flashes the green light on the PSXX (short cleared) for just an instant, then goes to red (shorted).  I can very carefully ease the loco between two shorted conditions with my hand, basically finding a mid-point in a very short distance rocking motion where there is no short circuit.  But the slightest motion in either direction reestablishes the short.

I am trying to decide whether to take the shell off and try to find and fix this myself, or sent it to BLI for repair.

Has anybody here had a similar experience with this or a similar BLI steam loco? If so, what did you find was causing it?

[jjb62556]

I would send it back..no need to open that can of worms on a new engine....

[Maletrain]

Because I removed the cab and separated the tender from the loco, I am not sure they will treat it as a new engine.

And, I do intend to take off the shell at some point to move the headlight.  So, unless this is something to do with the motor or the light board in the loco, it seems like I need to know how to fix it.  The way it developed seems odd, so I am hoping that somebody who has experience with these can recognize the symptoms and give me some hints. 

[prr7161]

1 amp on the breaker is low for a Paragon locomotive - I accidentally set a breaker to 1 amp vs. 5 (default) at one point and any BLI + any other loco would trip the circuit.  Paragons are current-hungry and it may be confusing the breaker.  Try setting the breaker amps higher and see if the problem still persists.

[peteski]

Did you actually take an ohmmeter or continuity tester and measure a short across the loco's wheels?

[NDave]

The "movement" (or lack thereof) and excess current/short observations sound somewhat similar to a problem I had with my Athearn challenger, tho' it was not "new" at the time (but had been run less than 50 hours).

It's symptoms: after running a lap or two, or less  (anywhere from 10 to 50 ft), it would erratically slow down and come back to speed, slow down again, and eventually come to a stop/stall. If I pushed it a little, or rocked it back and forth, or reversed direction, it MIGHT move a little further, before stopping again. If the loco was in the reversing loop on my layout when an "attack" occurred, it would set my AR-1 autoreverse to chattering... and in some cases trip the overcurrent protection in my NCE Powercab. These observations prompted me to turn on the current monitoring in my Powercab, which indicated that slowing and/or  stopping coincided with periods of excessive/extreme current draw. At first, I thought it had a mechanical bind... but I could never find evidence of one, and I realized that when the loco slowed/stopped, the current draw was more than twice the stall current of the motor... suggesting an electrical issue or short.

To make a long story short(er)... it turned out to be a problem with the motor. The "graphite" brushes apparently were too "soft" and had worn substantially, filling the motor (and inside of the loco frame) with a reddish, conductive, dust... when said conductive dust bridged the gaps in the motor commutator, the motor shorted out, and the loco slowed/stalled. I ordered a new motor from Athearn, installed it, and the challenger has been running great for 5+ years now.

I don't know that a new, hardly run, loco could have the same problem... but the symptoms sound very similar, so It might be something to look in to. Best of luck!

[Maletrain]

PRR7161, I have other N scale BLI Mikados, same model, but B&O road numbers instead of unlettered.  When I run those on the same setup, they draw 0.11 to 0.13 amp on speed step 40of128 - I can get it up to 0.16 amp with the bell ringing and the whistle blowing, headlight on.  So, remember, this is N  scale, and I am testing with a Power Cab.  The reason there is a breaker set for 1.0 amp is because anything over about 1.4 amps trips the Power Cab wall wart.  1 amp is plenty for one N scale loco.

Peteski, the loco reads about 3 ohms between the driver tires on the same axle.  It also reads about that or lower between any driver tire and the bottom plate screw that goes into the frame.  I am thinking that has to be a short to the frame, somewhere inside.  The decoder is disconnected (tender off), so I am wondering if the motor circuit can even be a part of the short circuit path.

NDave, I did think about the motor brushes fouling, because of the way this came on - like something was wearing really fast.  But I am wondering if it is something like the insulation on an internal wire getting cut-through by something that is in-motion when the loco runs.  There have been only minutes of run time, including attempted run time without actually running.

I was going to call BLI tech support to see if they have any ideas, but they are only  available noon to 4 pm on T-W-Th, and I won't be able to try that until Th.

[peteski]

Peteski, the loco reads about 3 ohms between the driver tires on the same axle.  It also reads about that or lower between any driver tire and the bottom plate screw that goes into the frame.  I am thinking that has to be a short to the frame, somewhere inside.  The decoder is disconnected (tender off), so I am wondering if the motor circuit can even be a part of the short circuit path.

http://www.broadway-limited2.com/support/N%20Light%20Mikado%20Locomotive%20Expl%20View.pdf

3 Ohms can be considered a short for sure.  This model uses split-frame chassis and the screw holes are on one of the halves, so it makes sense that it shows the same short as between the wheels.  It also explains why one side shows even lower resistance.  The side of the frame  with the screws will show dead short to the wheels which are on that side of the frame, and 3 ohms when measuring to the wheels on the other side.

The should could well be somewhere between the frame halves.

[Maletrain]

The gears seem to be mostly to the engineer's side of the frame, but the floor plate screws seem pretty close to centered.  So, I am guessing that they connect to the firemans's side of the frame.  I can't spend much time right now, trying to see if there is a detectable pattern to the resistances between various parts.  The values I get are not completely steady, and that tends to mask any real small differences.

[peteski]

I posted a link  to  the exploded parts diagram. If I chose the correct Mikado, I believe the diagram shows that the center 2 screws retaining the bottom plate are threaded into the right frame half (engineers), part #43, and the 2 outer screws are threaded into the left frame half, part #56.  So depending on which screw you were probing, you might get different results.

[Maletrain]

Peteski - thank you for the exploded diagram jpg. It prints dark enough to use the print, while trying to print the same drawing from the website comes out too faint to read on paper, for some reason.

Updating, the BLI techs e-mailed me to take off the pilot and trailing trucks to see if the short was with them.  It wasn't.

But, in trying to diagnose it more myself, I found that, without the tender, gently nudging the loco from the fireman's side could almost repeatedly open the short circuit.  Once it opened, nudging from the fireman's side again did not reshort it, but nudging from the engineer's side or the front or rear immediately recreated the short.  As I repeated the process to try to be sure that I could do it exactly right to always get the same results, it suddenly stopped shorting no matter how I nudged it. 

So, I put the tender back on the loco, and tried to run it.  But, it is now dead.  The tender is drawing 0.04 amp, but no motion, sound or lights (or short) from the loco.  Thinking I might not have made a good connection with the 4 wire (6? pin) connector in the tender, I unplugged and replugged that, with no better results.

So, at this point, I think I had best send it to BLI and let them figure it out.  But, I am going to hold onto it for a couple more weeks to get the next test fit of the 3D B&O cab.

[Maletrain]

 

It appeared to be dead because I brain-farted and picked up the throttle to the other loco I am working on. 

With the correctly addressed throttle, the loco is not dead after reassembly.  I got lights, sound and motion - for maybe a foot, then the short recurred.

Nudging the loco from the fireman's side does sometimes clear the short, for a fraction of a second.  Taking it off the track and putting it back with a Kato blue rerailer, it sometimes does not initially show a short.  But, it will short immediately if I try to start in reverse, and makes it maybe an inch or so in forward before shorting again.

So, basically still a short circuit problem that I am still thinking I will send back to BLI.

[peteski]

I think that in order to diagnose (and fix)  this will likely require full disassembly of the loco. If you're not up for that, sending it to BLI is probably the best option.

[Maletrain]

Yes, even if I can diagnose it, I may still need a part and a complete tear down to fix it.  I have better things to do with my time, since this is a brand new loco.