MTH PS2 Atlantic with Herky-Jerky motion--Solved!

RRDOC, looks like it could be a loose tether plug.  Check to see if the plug is fully seated; if the problem persists, you may need a new tether.  I just replaced the tether on my PRR Atlantic, same symptoms.

John

I'd re-clean and lube everything on the engine from the motor to the wheels and rods and rollers, including the tender wheels.

Dale

Classic signs of some binding in the geartrain or drive rods IMO.  If you run it in conventional mode on a flat track and turn off cruise control, you can see clearly if something is binding.

What should the speed be?  Is it supposed to be slow and all of a sudden it lurches forward?  Or is it supposed to be fast and at times it slows down?

If the former, I think you can eliminate the binding theory.   Binding would not cause a lurch forward.  Tether could be the key.  My son has a T1 with the same behaviors.  Of course, could also be a tac reader too.

If the latter, then maybe binding is involved.  But the motion is not consistent, I would think binding would occur in a pattern at the same place during a particular point in a revolution.

Have you tried running at different speeds to see if the results are the same?

Ron

Until you open it up and have a look around, this is all dart board diagnostics, ….everyone’s ideas are plausible, but guessing and hoping for a miracle gets time consuming & expensive,…..if it’s getting a respray anyways, now’s the time to open it up and have a look around,…..flood waters don’t stop on the outside…and. Just because you think it only “ dipped its toes in “ doesn’t mean the entire engine wasn’t exposed to moisture. and sometimes the exposure can be more damaging in the long run than a quick dip,……I’d be willing to bet the green monsters are lurking somewhere in that engine, ….it’s your job to find them!…🤣🤣🤣🤣….they can be eliminated, but that’s where the detective work comes in,….

Pat

My impression watching the video, I saw clear runaway increase in speed and lack of chuff at the same time. That typically is loss of tachometer- since it both is used to time chuff and control speed.

Given this was a tether, I was going to recommend the replacement tether whip, but then checked the manual and realized- even though this was a 20-31xxx-x steam product number, it's also PS2 5V and thus may not have the modular plug in tether whip (well that, and it's also a 5V........).

Again, to me, I would first check the tether plug, but also, that's a known failure point the tether can break wires internally and become intermittent and since tachometer signal goes back to the board in the tender, that's how you get both runaway and intermittent chuff.

Again, I saw sudden speed increases, along with loss of steady chuff, that did not appear to be opposite- slowdown and mechanical bind- pointing in my head at a more electrical wiring tachometer based route of troubleshooting.

BTW, that whip part number is BC0000217

however, again, being PS2 5V https://mthtrains.com/sites/de...ction/20st15166i.pdf

It looks to me like you might have to replace the whole harness or splice in the other style of whip.

maybe ???

Or the pain in the neck way splicing all 10 wires.

99% chance it's the tether like Vernon noted. When the locomotive tries to run away jiggle the tether and see if it comes back under control. Either the tether itself is bad or the receptacle on the locomotive side has loose pins. Repair of the tether receptacle involves reflowing the solder holding the pins in (easy), repair of the tether involves replacing the tether.

Thanks for posting the video, that helps a lot.  IMO this isn't valve gear binding, or anything mechanical.  As others have said, maybe a loose tether, or something with the cruise control.  I like GunRunnerJohn's idea of testing it in conventional mode with Cruise turned off.  Please post back with your findings.

@RRDOC posted:

Background:

I put I on the layout, started up in command, and this happened:

So are these accelerations a tach strip/tach reader problem or something else?  I did try a feature reset with no benefit.

Thanks

Bob

Can't give you better help than what you have getting now ........except.......KUDOS on posting a video .  Best kind of info to get possible assistance in an issue !

I had an 0-8-0 that ran like this. Mostly did it on corners when there was a little strain on the tether. Lou might have the fix in re flowing the solder on the PCB pin on the engine.

Thanks everyone.  Progress so far:

1.  I discovered a loose traction tire, which I replaced.  No joy.

2.  I sprayed the tether contacts with electrical contact cleaner and re-seated it.  No joy.

The pattern of runaway episodes is random, not occurring at the same point in wheel rotation, so I don't think it is a mechanical binding issue.  I'm leaning towards a tether/tach problem or maybe a loose flywheel.  As Pat pointed out, it's time to look under the hood.  And yes, there could be moisture damage inside.  There were certainly enough pock marks of corrosion on the shell probably from sitting in a humid wet basement and wet box.  

I was hoping for a quick fix as I have the grandkids arriving tomorrow for a 2-3 week visit.  Anyway, there may not be much troubleshooting progress for a couple of weeks, but I'll repost when I sort this out.

Bob

Keep us posted Bob, ……as the others have pointed out, it could very well be one of the above mentioned issues, but flood victims need extra scrutiny……the green monsters ( especially on soldered joints, etc. )  need to be hunted down and dealt with,…..copper wire can degrade and turn green from moisture intrusion,…..The tach sensor eye could be partially obscured with muck or stains…obviously you’ve gotten it running, so that alone is a Herculean feat, given the conditions you describe…….recently, a buddy of mine breathed life into a flood victim, and I wanna say he wound up doing just about a complete tear down to chase away the gremlins………

Pat

@Ron045 posted:

What should the speed be?  Is it supposed to be slow and all of a sudden it lurches forward?  Or is it supposed to be fast and at times it slows down?

If the former, I think you can eliminate the binding theory.   Binding would not cause a lurch forward.  Tether could be the key.  My son has a T1 with the same behaviors.  Of course, could also be a tac reader too.

If the latter, then maybe binding is involved.  But the motion is not consistent, I would think binding would occur in a pattern at the same place during a particular point in a revolution.

Have you tried running at different speeds to see if the results are the same?

Ron

The speed is set low and it lurches forward.  It happens at medium speed as well.  I just pulled the loco shell and no sign of water damage so far.  Tach strip is good, optical reader is in place and flywheel is not loose.  No binding when I turn the flywheel by hand.   Next I will put it up on the test stand and manipulate the tether to see if I can reproduce the lurch.

Bob

@RRDOC posted:

The speed is set low and it lurches forward.  It happens at medium speed as well.  I just pulled the loco shell and no sign of water damage so far.  Tach strip is good, optical reader is in place and flywheel is not loose.  No binding when I turn the flywheel by hand.   Next I will put it up on the test stand and manipulate the tether to see if I can reproduce the lurch.

Bob

Bob, while you’re in there, put a dot of oil on each end of the motor shaft, and inspect your gearbox for any moisture contaminated grease,……also oil the worm shaft end bearings. Then rotate the assembly by hand ( by turning the flywheel) and feel for any binding. That will eliminate the mechanical possibilities.

Pat

It was a flood victim so the solder joints can be issue.  Rear engine PCB having loose solder joint.  Mux board connections corroded to tach.  Faulty tach sensor.  Tether bad.  G

@harmonyards posted:

Bob, while you’re in there, put a dot of oil on each end of the motor shaft, and inspect your gearbox for any moisture contaminated grease,……also oil the worm shaft end bearings. Then rotate the assembly by hand ( by turning the flywheel) and feel for any binding. That will eliminate the mechanical possibilities.

Pat

Thanks Pat. Will do.

Solved!  As Pat put it, it was the "green monster" --  corrosion on the tether contacts.

Fortunately there was no corrosion on any boards or wire connections in the boiler or tender.  

Here is the loco on the rollers.  When I manipulate the tether, it reproduces the lurch.  Oddly, when I manipulate the roller that has the center rail power contact, it also causes the lurch (I am moving the frame when I did this, so maybe it was moving the tether slightly).

I sprayed it a couple of times with Ideal electrical switch and contact cleaner and plugged and unplugged it repeatedly.  It resolved the problem for now.

I'm not sure that this contact cleaner will be a permanent solution and I may need to bite the bullet and replace the tether as Vernon suggested.   Any suggestions of a better product that would remove the corrosion?  

Bob

Bob, a tether is pretty cheap, ….you’ll spend more money trying to breathe life into the infected one, then you’ll ever spend simply replacing it,….

Pat

Congrats on your persistence and solution.  You have a great treasure there.  Can't wait to see when you have it all finished.

Ron

The switch and contact spray is a great idea Bob.    Glad you were able to find the issue.

Corrosion will also get into the wires under the insulation and the spray should be thin enough to travel up those wires.

   I don't know if that NO-OX that the people on the forum use for rails and wheels and pickup rollers to stop corrosion will work or not.  Also maybe some of that protectorant used on battery posts.

Good luck and have fun.

@Vernon Barry posted:

BTW, that whip part number is BC0000217

Here is the current tether:

It is the BC0000217 with the sheath stripped back, right?

If so, I won't have to splice all the wires, so replacing it is a no brainer.

Bob

@RRDOC posted:

Here is the current tether:

It is the BC0000217 with the sheath stripped back, right?

If so, I won't have to splice all the wires, so replacing it is a no brainer.

Bob

You can use the one Vernon suggested, …..it should fit just fine, ……you may or may not have to peel back some of the sleeve on the straight plug, it’ll all just depend how it’ll route in the tender and exit the hole …….try it as is out the package, and only mod it if you run into cable management issues,….

Pat

I thought I would update this thread with the finished engine repainted and decaled.  The jerky motion problem resurfaced even after replacing the tender tether.  After much trial and error, the solution ended up being to re-flow the solder joints of the pins of the tether jack on the locomotive.   After this success, I tried the original tether again and the jerky motion returned.  Turns out I had BOTH a bad tether and bad solder joints on the jack.

Thanks to everyone who offered suggestions.  Enjoy the final result.

Bob

@RRDOC posted:

I thought I would update this thread with the finished engine       Thanks to everyone who offered suggestions.  Enjoy the final result.

Bob

Beautiful Bob.      Great operation.