MTH Restoration Big Boy Issue or not?

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

Not all the drivers are electrically tied together when the switch is in the 3-rail position.  You could have a bad 2/3 rail switch or the power pickup on the split axle of the driver is not making contact.  Somewhat common on these locos and diesels.  Easiest solution is to tie both outside rails together.

@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.

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

@Vernon Barry posted:

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?

Yes you should but you going through resistive connections between wheel, axle, chassis screw, axle wipers.  To check the switch just measure continuity at the terminals.  If 0 ohm the switch is good.  G

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.