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So I am an owner of the latest Glossy black restoration Big Boy. My question is.....Should I have continuity between the wheels of this locomotive? (same axle wheel to wheel) I realize there is a 2 rail/3 rail switch on the bottom of the tender. I am thinking the reason I dont have continuity between wheels is because if the loco was switched to 2 rail and if I had continuity that would be an issue on 2 rail track. So if I flip the switch to 3 rail....Should I get continuity between the wheels? Well I dont. And it seems DCS does not want to find this loco unless I have either a jumper between the outer rails or add a freight car to simulate a jumper between the outer rails. Is this normal?

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This is from MTH  "3-rail locomotives equipped with the all-new Proto-Scale 32 feature can be operated on 3 or 2-rail track under AC or DC power. A small switch will redirect track power from the center rail pickups to the locomotives left side drive wheels. Ground will move from all locomotive wheels on 3-rail operation to the left side locomotive wheels on 2-rail track."  (this does not make sense to me - one should be left the other right - i am probably missing something in translation)

I have the new oil version, runs great no issues on 3 rail.  Sounds to me you have your outer rails electrically isolated. Presumably the switch in 3 rail position will flow current out through either wheel on any particular axle.  From what you describe that is not happening. So when you run 3 rail you would need to provide a connection between the TIU and both outer rails or provide a connection in another place such as a normal 3 rail car as you describe.  It may be worth flipping the engine around to confirm you have a ground issue.  Should work fine one direction and have issues the other direction if the outer rails are isolated. I suppose it could be a faulty switch or a loose/broken ground wire connection. If there are diodes in the circuit you will not detect continuity between the wheels.

This feature has been around a long time, maybe one of the forum techs will show how these are wired.

   

Scouting dad, I have found by turning the locomotive around DCS will find it. Yes, I do have my outer rails isolated because I am using MTH realtrax with MTH's power lockon which only sends the negative to one outer rail. Is this typical on all 2/3 rail proto3 locos. I have other p3 locos without the 2/3 rail switch that show continuity between wheels on the same axle. So, by switch being in 3 rail, should I read continuity between wheels on the same axle? Even if there is a diode in the circuit, I am metering directly between 2 wheels on the same axle. So is it absolutely necessary to have both outer rails tied to ground? If so I am beginning to see that MTH's track power lockon is not really designed for a 3/2 rail loco.

The issue is not with the power lock-on, but with your choice of track.  Any lock-on provides power to only one rail (the center rail in 3-rail track) and requires ground (return) from the outer rail(s) of 3-rail track, but the lock-on is only connected to 1 of those 2 outer rails.  Both outer rails can provide ground  for the circuit only if the manufacturer electrically connects them like the original Lionel O27 or O gauge track where the metal ties create the outer rail electrical connection.  With that connection, Lionel had to insulate the center rails with little pads between the center rail and the metal ties to prevent a short circuit with every tie.

When you throw that 3/2 switch on your engine, the engine is now looking for power from one of the outside rails, which power is now flowing through ground on the opposite outside rail.  Unless there is something I don't understand, your lock-on just can't work in the usual 3-rail track situation.

Chuck

Last edited by PRR1950
@jini5 posted:

So I am an owner of the latest Glossy black restoration Big Boy. My question is.....Should I have continuity between the wheels of this locomotive? (same axle wheel to wheel) I realize there is a 2 rail/3 rail switch on the bottom of the tender. I am thinking the reason I dont have continuity between wheels is because if the loco was switched to 2 rail and if I had continuity that would be an issue on 2 rail track. So if I flip the switch to 3 rail....Should I get continuity between the wheels? Well I dont. And it seems DCS does not want to find this loco unless I have either a jumper between the outer rails or add a freight car to simulate a jumper between the outer rails. Is this normal?

There are several electrical reasons why a multimeter might not show continuity between the the left and right wheels, but it shouldn't matter for DCS since the signal is on the center rail.

I'm wondering if you have the wires between the TIU and the track crossed somewhere.

Is this PS-3?  Regardless, the 2R-3R switch on the tender only connects the tender wheels together and properly routes engine wiring.  The engine wheels remain separate.  Right side as a source of AC power only in 2R.  If you are a 3R only you can go in and move the right side wires and ground them to the chassis so both side provide ground.

PS-3 does not care about polarity.  PS-2 does which is why they also have a polarity switch to ensure the rail with Red DC signal get to the red wire of the PS-2 board.  G

@GGG posted:

Is this PS-3?  Regardless, the 2R-3R switch on the tender only connects the tender wheels together and properly routes engine wiring.  The engine wheels remain separate.  Right side as a source of AC power only in 2R.  If you are a 3R only you can go in and move the right side wires and ground them to the chassis so both side provide ground.

PS-3 does not care about polarity.  PS-2 does which is why they also have a polarity switch to ensure the rail with Red DC signal get to the red wire of the PS-2 board.  G

PS-3 doesn't care about polarity, but if the wires are reversed after the TIU, the DCS signal would be on the outside rails which are not always connected depending how the blocks are set up, especially for non-derailing switch operation, no?

@rplst8 posted:

PS-3 doesn't care about polarity, but if the wires are reversed after the TIU, the DCS signal would be on the outside rails which are not always connected depending how the blocks are set up, especially for non-derailing switch operation, no?

Well a minor issue is you said earlier DCS was only on the center rail and IMO that is wrong.

DCS is a signal embedded in the power on the rails. So no, it's on BOTH rails middle and outside.

TMCC is a radio signal. A lower frequency one, but a Radio signal. That radio signal, the outside rails form one half, the house wiring is the other half.

DCS is an in-band signal and again, is the difference between the 2 rails electrically.

Well a minor issue is you said earlier DCS was only on the center rail and IMO that is wrong.

DCS is a signal embedded in the power on the rails. So no, it's on BOTH rails middle and outside.

TMCC is a radio signal. A lower frequency one, but a Radio signal. That radio signal, the outside rails form one half, the house wiring is the other half.

DCS is an in-band signal and again, is the difference between the 2 rails electrically.

In my case, I had a bunch of PS2 locomotives become unable to be found by DCS (even though they were already in the remote), until I swapped the wires at the lockon. The one diesel that continued to function was a PS-3 unit. I hadn't suspected reversed wires because that particular unit was the only one on the layout before and after some wiring rearrangements that ultimately reversed the sole track connection, and being PS-3, it didn't care. But the PS-2 units did.

---PCJ

MTH engine wiring is quirkier than I thought. Funny how the PS2s had issues. Every once in a while I have trouble finding locos, sometimes its how I am connecting through the TIU others may be the outside rails to common.  I kept mine separate thinking I might want to have signal blocks indicating when the section was occupied. I have found I needed to connect the outside rails on my Ross turnouts. Too easy to lose power going through a curve. My outside rails are connected to common and the inside rail are not (although its easy enough to connect).   

@harmonyards posted:

I just do what George recommends, ….very simple solution if sticking with 3 rail track….run a jumper wire from the axle wiper ( outside rail ) to the frame, ….ain’t like there’s no shortage of frame screws to put an eyelet on,….grounding to the frame picks up a whole bunch more wheels…..😁

Pat

If there's already an axle wiper, what does grounding it to the frame do? There's no guarantee that there is good electrical conductivity between the frame and the wheels, is there?

@rplst8 posted:

If there's already an axle wiper, what does grounding it to the frame do? There's no guarantee that there is good electrical conductivity between the frame and the wheels, is there?

Yeah,….it does ….the wheels that have the wiper are isolated for the 3/2 option,….all later Premier are built that way,….all older 3 rail engines rely on the axle completing the circuit through the frame ….so add a frame ground on 3/2 optioned engines, you pick up the rest of the wheels for ground ( outside rails)

Pat

@harmonyards posted:

Yeah,….it does ….the wheels that have the wiper are isolated for the 3/2 option,….all later Premier are built that way,….all older 3 rail engines rely on the axle completing the circuit through the frame ….so add a frame ground on 3/2 optioned engines, you pick up the rest of the wheels for ground ( outside rails)

Pat

Pat,

I'm not trying to be contentious, and I respect your and GGG's opinions and experience on these things... but I have PS-2 3v models that have wipers on a tender truck which connect to the internal board for power. If a wiper was needed in those early PS-2 models, where the wheels were NOT isolated, I fail to see how a chassis/frame connection would offer much help especially if the bushings are well oiled and the wheels on each side of the loco are not connected.

It seems to me that more wipers would be required and those tied to the lead going to the board.

@rplst8 posted:

Pat,

I'm not trying to be contentious, and I respect your and GGG's opinions and experience on these things... but I have PS-2 3v models that have wipers on a tender truck which connect to the internal board for power. If a wiper was needed in those early PS-2 models, where the wheels were NOT isolated, I fail to see how a chassis/frame connection would offer much help especially if the bushings are well oiled and the wheels on each side of the loco are not connected.

It seems to me that more wipers would be required and those tied to the lead going to the board.

I don’t think you’re being contentious,…..if I did, I’d jump through the screen with both feet….🤣🤣🤣🤣🤣….

It’s a case of the more the merrier, ….we add commons wherever we can when the need arrives,….and it will complete the circuit going through the wheel, through the axle, through the bushing, and to the frame……we even add a ground wire from the pilot truck to the frame for added grounds, …..when it’s sitting still, the connection you’re thinking of maybe poor, but when rolling, they’ll complete a circuit in a jiffy,…..Lou had recommended adding a leader to one of my engines having a stuttering problem over #5 switches,….ever since then, I’ve made it common practice ….

Pat

Some engines are more finicky than others especially with dirty wheels and such.  Engine and tender wheel are isolated on one side.  Normal PS-2 would have both sides of engine and tender providing AC ground.  Pickup rollers from engine for center rail.

When you get to PS-2 or 3 with 3-2 rail, you loose the engine ground wire and you only get half the tender wheel.  Engine only provides ground via metal drawbar, or that drawbar pin on plastic drawbars.  The tender switch will connect both sides of tender wheels together if switch works correctly and is not damaged. G

@GGG posted:

Some engines are more finicky than others especially with dirty wheels and such.  Engine and tender wheel are isolated on one side.  Normal PS-2 would have both sides of engine and tender providing AC ground.  Pickup rollers from engine for center rail.

When you get to PS-2 or 3 with 3-2 rail, you loose the engine ground wire and you only get half the tender wheel.  Engine only provides ground via metal drawbar, or that drawbar pin on plastic drawbars.  The tender switch will connect both sides of tender wheels together if switch works correctly and is not damaged. G

So with the tender 2/3 rail switch in 3 rail, will I read continuity between both wheels on an axle? If not, how do I confirm the switch is defective?

OK thanks to all who have replied. So I spent a few minutes to confirm what I have been saying all along. This loco 20-3807-1 must have a negative from the transformer (through TIU) on the conductor side of the loco or DCS will not find it. My present layout is MTH realtrax with one MTH track lock on. As you can see from the pics...........if loco is facing the right DCS finds it. If loco is facing left DCS will not find it. Yes yes I get it that any freight car behind the loco would act as a jumper between the 2 outer ground rails. Or maybe I could tear up the layout and solder jumpers between the 2 outer rails at various locations may also solve this. Or I coiuld run this loco in only one direction with conductor side receiving the ground from the TIU.

HOWEVER.......................... what if I have no desire to tear up the layout or run in only one direction, or pull freight cars acting as ground jumpers?

Am I correct in assuming this loco should work with the 3/2 rail switch in the 3 rail position and either outer rail grounded but not both? Is it written somewhere that both outer rails must be grounded for this loco to operate? MTH's realtrax and their lockon only ground one rail.

This is still under warranty. I dont want to tear into it due to losing the warranty. If I have a connection inside the loco or a faulty 2/3 rail switch, shouldn't this go back to my dealer for a refund? I don't have anywhere to turn except for the dealer I bought it from. He is a fully authoried dealer who does not do repairs. I doubt he has extras laying aroud and I doubt he will want to do a refund.

So ............as the title of this thread asks................Do I have an issue or not with this loco? I am thinking that if this loco can't operate unless both outer rails are grounded then there is an issue. After all MTH's track system is designed with only one rail being grounded.

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Images (3)
  • DSCF4353: no active dcs engine when engine faces left
  • DSCF4354 (1): DCS finds this loco facing to the right
  • DSCF4354
@Jon G posted:

My guess is a bad 2/3 rail switch.  I replaced a few when in service.  Kinda pain because its buried in the centipede truck.  You can access it for by removing the shell and electrically testing the switch and ensuring the wire nuts are properly connected.  Easiest solution is to bypass the switch at the wire nuts.  99% of the hi-rail operators run 3-rail anyway.

Thanks Jon.......So I am correct that this loco should run with only 1 rail grounded ?. Again, If I open I void the warranty. How many leads are on that switch? How would I know where to check for continuity?

@jini5 posted:

Thanks Jon.......So I am correct that this loco should run with only 1 rail grounded ?. Again, If I open I void the warranty. How many leads are on that switch? How would I know where to check for continuity?

Yes, should work with one side grounded, but that’s not optimal.

The tender has 6 screws securing the shell.  You won’t void the warranty removing the shell.  Just be careful to not pinch the chains or wires when reassembling.

The switch has 4 leads and a crossover wire on the 6 terminals.  Check continuity between the center terminals and each end terminal with the switch in the tested direction.  If bad, suggest following Gunrunner’s diagram to bypass it or use the ASC locator to find an authorized service center.

Andy works part time for MTH and Atlas, from home.  Rich Foster is the only one in the office taking calls.

So, is there  a possibility that the nameplate for the 3/2 rail switch was put on backwards at the factory? What will happen if I power the loco then switch the switch to 2 rail?If in fact the switch is correct and by switching the switch to 2 rail, I actually activate the 2 rail mode.....Am I going to blow some board somewhere on this loco?

This is PS-3 BB correct?  John's picture is PS-2 3V and not correct for PS-3.  No polarity switch.  The Engine Right side wheels pick up via spring plungers.  The Left Side are chassis ground.  Only right side wheels and center pickup go to the 6 pin drawbar to send power to tender.  The left side of engine can only make connection via the wire pin along the drawbar.

Tender wheels have to provide ground through the axle wiper, friction contact of truck and switch.

If you have a non 3R-2R engine and it runs fine on layout, I would go into engine and connect the engine right side wire to chassis ground.  Now Engine both side wheels and the center pickup have AC track power via drawbar to the tender.  Now you have better continuity of power for the enigne for 3R.  Easy to reverse if you want to run 2R at a later date or sell engine.  G

@GGG posted:

This is PS-3 BB correct?  John's picture is PS-2 3V and not correct for PS-3.  No polarity switch.  The Engine Right side wheels pick up via spring plungers.  The Left Side are chassis ground.  Only right side wheels and center pickup go to the 6 pin drawbar to send power to tender.  The left side of engine can only make connection via the wire pin along the drawbar.

Tender wheels have to provide ground through the axle wiper, friction contact of truck and switch.

If you have a non 3R-2R engine and it runs fine on layout, I would go into engine and connect the engine right side wire to chassis ground.  Now Engine both side wheels and the center pickup have AC track power via drawbar to the tender.  Now you have better continuity of power for the enigne for 3R.  Easy to reverse if you want to run 2R at a later date or sell engine.  G

GGG yes it is ps3 the latest MTH restoration big boy in glossy paint. It wont run at all if the firemann/conductor side outer rail is not connected to ground via z4000/TIU.( DCS wont find the loco). I don't believe it is up to me to go into this loco and void the warranty. Rich at MTH reached out to me in an email but I have not heard back from him in a few days. Not sure where I am at with this. When I do get it to run it will not pull worth a s.....! I am comparing this new p3 loco to my p2 big boy. My p2 will walk up my grades at 5 SMPH  with 7 Lionel 21" cars and a heavy diecast tender. This new p3 will barely if at all make it up the grade at 5MPH with only the diecast tender. So there are more issues with this loco. Hopefully MTH gets back to me. Looking like it will go back to my dealer probably for a refund. Not happy I waited over a year and find myself out of luck. This is why I don't care for built to order.

FWIW, not bad mouthing MTH but I have seen issues with this new Big Boy I have not seen with any other of my engines, I have almost 300 engines of PS2 and 3 so when they all work fine on the same layout but this new Big Boy will not work correctly, it's the new Big Boy engine.

My two cents is the board for the reciever is not as strong as the prior PS3 were and this makes it have issues that the other PS3 engines don't have. It just doesn't have the signal strength so you have to have better grounds and connections to make it work. If you have solid 10's then you will not see an issue, but even a signal strength of a 9 will make the engine not receive commands. I even lashed up another PS3 steam engine to the new Big Boy, didn't couple them together and ran them on the same track behind each other. The other PS3 responded to every command issued where the new Big Boy sometimes did and sometimes didn't. So I could slow down the old PS3 steam engine while the new Big Boy stayed at the same speed it was at prior to me issues a speed command to slow down. So real world proof is it's an issue with the new Big Boy engine.

For this thread I agree it's most likely that 2/3 switch. We all know those switches are just bad and fail all the time.

So far I have had to replace the marker lights, bad wireless draw bar, make better connections in the tender for all grounds and fix the tender trailing truck the factory forgot to tighten the screws as it fell apart. It now works better but still not to the the level of my other 100 plus PS3 engines I have.

Work on the grounds and anything that will make the signal strength better will improve this engine. I agree with you, you should not have to work on a new engine to make it work on a normal layout. Especially when all your other engines work fine.

Last edited by Jeff Green

On the issue of it not pulling good at low speed, this is not a problem with the engine as that's how it is made to work.

Few may know, unless you pull long heavy trains, that all PS3's stall when too much load is applied at low speeds. The old PS2's were stump pullers and would keep appling more amps to the motors until the speed was reached. Because of this PS2's would throw traction tires if you ran them in lash-ups as they would fight each other some. PS3's don't do this, because they stall, and you will not see the traction tire issue on them.

So PS2's will start any length or weight of train unless they actually can spin their wheels from the weight. PS3 will not start a long heavy train no matter how many PS3 engines you have on the headend because they all will "stall".

The good about this is PS3's are great to run in the middle or rear of a train, like they do in PSR or rear helpers in real railroading, because they will not wreck the train by pushing in the slack. PS2's would wreck a long train if you ran them at the end or middle because they were not a perfect speed to each other and if the head engine had just a blip, the rear engine would push the train in past the slack.

For diesel lash-ups, putting one PS2 in the headend with other PS3's helps to start the train by pushing the PS3's past their stall point.

So depending on what you want to do can make a difference rather a PS2 or PS3 is the best engine to use.

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