Model Power Mogul Stalling

[Mindheim]

Since their introduction, I've picked up a number of Model Power Moguls.  I've found them to have an exceptionally smooth running mechanism and love the detail.  Very economically priced too.  One problem, after a short period of use every...single....one of them has started to exhibit maddening intermittent stalling.  Both myself, and experienced friends have taken them apart, cleaned and examined every square millimeter of them, and haven't been able to find the source of the problem.

I know it's not the track because the issue occurs on a clean straight section of Peco test track.  In fact, if I hold the loco. loosely in place on the test track the drivers will spin and then, without reason, it will stall.  The decoder leads were twisted in place and I've soldered those.  Through testing I know ALL wheels, tender and loco. are reliably picking up power.  I took a close look at the copper pickups as they have shown signs of wear where the copper has worn off.  I'm beginning to doubt this is the issue though.  When they're stalled, if I stick a toothpick between the driver spokes and gently wiggle it, the unit starts again.  In fact, lightly tapping the loco. anywhere on the shell will often get it running.

Could have to do with the metal coating on the wheels?  Doubt it as the tender wheels are fine.  Could it have to do with something inside the motor itself?  As the unit warms up, the problem lessons but doesn't disappear entirely.   I'm at a loss.
Lance

[Point353]

The report by Spookshow mentions that the mechanism can develop a bind, which may possibly be resolved by adjusting the tightness of retaining screws for the driver cover plate.
Have you perhaps tried making such an adjustment?
http://www.spookshow.net/loco/mp260.html

[brokemoto]

Are you running the originals with the half-wheels live tender or the MRC versions?  The MRC versions have all wheels live tenders, so you should not be having a problem with those.  The original MP versions have only a half wheels live tender.  The presence of the traction tyre will compromise the contact from the drivers.  The half wheels live tender provides insufficient contact.

If it is the original MP issues, you have options. 

You can go to the B-mann SPECTRUM USRA short or USRA standard tender.  If you are a DCC user, get the more recent issues with the prongs in the tender.  Even if you are not a DCC user, those with the prongs are easier to work with, as you connect the wires to the two outer prongs on either side.  If you get an older issue SPECTRUM tender, there are no prongs and the contact strips in the tender are held in place by melted plastic nubs.  If you want to solder a wire to them, you had better be very skilled with a soldering iron, lest you melt the plastic on the tender.  You can remove the strips, but, you then must find a way to secure them back.  You can fashion a hold down from plastic and screw it into the tender floor with MT coupler screws.

You can use a Kato USRA standard.  A clip holds the contact strips to the tender floor.  You simply remove the clip, remove the strips, solder your wire, replace the strips, replace the clip.

If you want to retain the  rectangular tender of the original, I understand that it will fit the chassis of the SPECTRUM slope back with a minimum of surgery.

I have done all of the above, save the rectangular tender to slope back chassis.  I have done this to the original MP versions.  I do not have any of the MRC versions, although I understand that the tenders are all wheels live.  I have both versions of the eight wheeler.  I added all wheels live tenders to the originals.  The one MRC version that I have already has an all wheels live tender.

If you do swap out the tenders,  you must, of course, adapt the drawbars or fashion new ones.

When dealing with N scale steam, it is always important to keep in mind Miranda's Maxim as explained by ke:

"The poor performance of many N scale steam locomotives is almost always directly attributable to poor electrical contact."

[Chris333]

You could also put Kato tender trucks under the MP tender. I remember their tender wheels looked like they were made of 100 grit sand paper. Plus those one side pick-up wipers from the caveman era.

Then there are the stiff wires that run through the drawbar and connect to the driver wipers inside the loco, if those are broken the tender might not be doing anything. With N scale steam the tender pickups do most of the work.

I could go on and on about Model Power steam. Haven't played with the MRC version yet.

[Chris333]

To add (it's been a while) I think the power from the drivers goes through their pick-up wipers and then a wire soldered to those pick-ups and makes a tight bend into the draw bar. In the tender they join the tender trucks (again I haven't seen the newer MRC models). The wire goes back through the draw bar and makes another tight bend to the back of the motor. They are stiff wires.

This shows the older tender trucks and the newer MRC versions:
http://www.spookshow.net/loco/mp260.html

The newer MRC tender trucks mimic the Kato style pick-ups so all 8 tender wheels do the work.

Other than that I know very little about DCC, perhaps a keep alive cap would help.

[peteski]

Is the loco in question running with a DCC decoder (that was not mentioned).  If yes, then the best way to troubleshoot these types of problems is by eliminating (physically removing) the decoder and testing the model under DC power.

[Point353]

Is the loco in question running with a DCC decoder (that was not mentioned).  If yes, then the best way to troubleshoot these types of problems is by eliminating (physically removing) the decoder and testing the model under DC power.

The OP did mention - in the second paragraph - that "The decoder leads were twisted in place and I've soldered those."

[Mindheim]

In answer to a few questions, this is the latest model unit.  I've cleaned (actually polished) every conceivable pick up point.  After months of going down the electrical pickup path my gut tells me that the suggestion in an early response that it may actually be a mechanical binding issue ( a super small one) has me leaning in that direction.  I did loosen the cover plate screws slightly. Can't say if that helped or not.  With the holiday I've been running it all day and with each hour it's running smoother and smoother (as with the case with a lot of n scale locos.  they like to be run).  Again, I do think these are exceptional locos.  The slow speed running smoothness is out of this world.

[peteski]

The OP did mention - in the second paragraph - that "The decoder leads were twisted in place and I've soldered those."

   Allrighty then! Then remove the decoder and test the locos performance in DC.

But first, the other thing to monitor is the headlight.  When the loco stalls, if the headlight is still on, then the power pickup is not the problem.  But it still could be motor wiring, or (less likely, but still possible) the motor.

Does the loco stall only at slow speeds, or at any speed?

[Chris333]

In answer to a few questions, this is the latest model unit.  I've cleaned (actually polished) every conceivable pick up point.  After months of going down the electrical pickup path my gut tells me that the suggestion in an early response that it may actually be a mechanical binding issue ( a super small one) has me leaning in that direction.  I did loosen the cover plate screws slightly. Can't say if that helped or not.  With the holiday I've been running it all day and with each hour it's running smoother and smoother (as with the case with a lot of n scale locos.  they like to be run).  Again, I do think these are exceptional locos.  The slow speed running smoothness is out of this world.

The drivers can slip easy on their axles (no splines, even the new MRC ones). I'd eyeball it for a driver out of quarter.

I know the headlight used to just wipe the front drivers for power, not sure if MRC changed that.

[peteski]

I know the headlight used to just wipe the front drivers for power, not sure if MRC changed that.

That is correct. I just figured that when MRC installed the decoder, they wired the headlight to the tender (so it could be controlled from the decoder).  I could be wrong . . .

[Chris333]

As on the revised Mikado and Pacific models, wiring for DCC headlight control was also added to these models. Unfortunately, only one wire (running back to the tender) was added. As pictured below, right-rail current for the headlight still comes from one of those annoying metal contacts running down to the driver pickup -

[peteski]

Wow!  I'm failing comprehension miserably today.    Looks like MRC took a crappy shortcut with the headlight.
I better turn in for the night (see how long that lasts). 

[mmagliaro]

Headlight hokiness notwithstanding, you need to determine if this is a pickup or a jam issue before attempting to fix it.

Since the headlight is not a reliable indicator, hook an ammeter in-line to the track and run until it stalls.  If the ammeter is not reading zero, then you have a mechanical jam.  If it reads zero, then it's a pickup problem.

FYI, even among the early 1st-run issues of the Mogul, it was probably the best-running of all the MP steam because it had the good 5-pole Mashima motor in it that they used only on the Mogul and 4-4-0, it had traction tires for good pulling, and it was geared nice and low.

So, let's find out about the ammeter reading.  Without that, you'll never know what the real problem is.

[peteski]

Since the headlight is not a reliable indicator, hook an ammeter in-line to the track and run until it stalls.  If the ammeter is not reading zero, then you have a mechanical jam.  If it reads zero, then it's a pickup problem.

Make sure to use AC range on the ammeter (since it is DCC).
Also, if the problem is not with the electric pickup, but with the motor wiring or with the motor itself, then the decoder will still be consuming some current when stalled. If it is a sound decoder then the decoder's current could be significant (let's say 50mA or more).  It probably makes sense to measure the idle current of the decoder (when the loco is powered but motor not running), to have a baseline of the current .