2-8-0 shorting out

[richG]

In case you ever want to add more tender wipers, here is what I did with my Spectrum 4-4-0 and 4-6-0 since the tender trucks only pickup on one side. I used Harold's idea.
Harold's site has been gone for over two weeks but I downloaded a lot of his stuff.
Harold's photo.


Bottom view of my tender.



The new Roundhouse tender trucks pickup from all four wheels and are designed to limit swiveling in case you ever get a Roundhouse steamer. I am upgrading my older MDC tenders with the new Roundhouse parts.



Rich

[shawneehawk]

Thanks to all for trying to help with this problem.  Sometimes when I get frustrated it is best to walk away for a day or two.  I checked the loco again last night, and am getting the same symptoms...it runs for a foot or two, then stops. 

I am forgetting about the Tsunami for now; this loco now has severe problems on DC.  It has not run right since I removed the bottom plated to check the wipers.  I have rechecked and cannot find the reason for this problem.  The tender trucks and wipers appear ok.  When the loco stalls I do get a buzzing sound around the rear tender truck but cannot find the reason for it.  Perhaps it is the circuit board??   

[Jim Banner]

Bob, thanks for the reminder about the pickup article.  Here is the link:

http://members.shaw.ca/the.trainman/LV_Workshop/pesky-pickups/

Hope it helps.

[Yampa Bob]

Jim, thanks for posting it again.  I hate it when I lose a favorite link.

I'm preparing to fine tune another Connie, this time I'll take some pictures of my bottom plate modification.  On the last one, I was tempted to trim the brakes a bit, pesky little critters.

[shawneehawk]

In checking the wipers in the bottom plate again, I found that the end of one easily broke off.  Looks like I will be ordering part # H11410 tomorrow...Bob, you think the new one will fit on my loco?

[Yampa Bob]

The new underframe comes prewired with a plug, and should fit ok.  When you snap on the "bottom plate", make sure the wipers move freely before installing the assembly. 

Sometimes while assembling, the plate falls off.  If it does, tie it on with a couple pieces of thread.  Once in place, cut the threads and pull them out.

Take your time and watch all the wipers while assembling. They tend to hang up on the wheel rims.  You will need fine tweezers to gently move the wipers in place on back of wheels.  Slooooow is the key.

Once in place, start the screws but don't tighten them all the way. Move each drive wheel side to side and observe that the wipers are following the motion to maintain contact.  If one or more wipers dont move with the wheels, the bottom plate has shifted and pinching the long part of wiper along the side channel.  You may have to remove and start over.

Be careful not to bite your tongue in the process. 

[Joe Satnik]

Dear All,

This may not be exactly the problem with this case, sorry if it is a distraction. (I have not thoroughly read this entire thread.)

I seem to recall a case (thread) where a DCC socket in a tender was shorted where its pins were soldered to the PC board.

It just so happened that those shorted pins imitated the DC jumper (shorting) plug, so it ran fine in DC, but failed when you plugged in a DCC decoder. 

Moral of the story: inspect for solder bridges on the PC board.  Another possibility: wires soldered to the wrong place on the PC board. 

Hope this helps. 

Sincerely,

Joe Satnik   

[Yampa Bob]

Thanks, Joe, for jogging my memory.  On one of my Connies, there was a solder bridge in the connector plug at the front of the tender. I used a thin edge file to carefully remove the bridge.

Now I make it a practice to inspect the plug, visually or with an ohmmeter, of any new locomotive before attempting to run. My "pre-inspection" list is growing as new elements of "Murphy's Law" show up.

As I mentioned in another thread, I never place a new locomotive on the tracks without a thorough inspection of everything that might be a potential problem.

[shawneehawk]

Thanks, Joe.  I checked and could find no solder bridges.  I have wondered if there was something wrong with the circuit board.

The loco ran fine in DC until I removed the bottom plate and tried to adjust the wipers.  I have ordered the underframe replacement, and hopefully that will do the trick.  If it doesn't, I will have to send the loco and decoder off to be inspected and repaired...something I'm really trying to avoid.

[shawneehawk]

This has turned into a comedy of errors.  The new bottom plate arrived, and I was able to get it positioned.  Thanks for telling me about the string trick, Bob.  BTW, the new one was identical to the one being replaced.  The loco continued to run erratically.  At first it ran good in forward, but wouldn't hardly budge in reverse.  Then I was able to get it to run in reverse but not forward.  Now, the front truck on the tender appears  frozen, and will not swivel.  I took the nut off the top, and the screw holding the truck will not remove.  It looks like it has melted the plastic around it.   

[shawneehawk]

Looks like I would have to order the tender chassis, tender truck wheels, and pcb assembly to be safe.  I talked with Bachman customer service, and they said to mail it in and they would fix it for $20.  I'm not sure they understood the scope of the problems I've had with this loco, however.  I certainly would not want to send my custom lettered tender and body shell in, too.  The only other option I can think of would be to send it to Tony's, and let them figure it out, including the decoder.  But since I could read the Tsunami on the programming track, I believe it is ok and these are strictly DC issues on the loco.  Anyway, I am getting some money tied up in this loco.

[Jim Banner]

Now, the front truck on the tender appears  frozen, and will not swivel.  I took the nut off the top, and the screw holding the truck will not remove.  It looks like it has melted the plastic around it.   

It takes heat to melt plastic.  Electric current flowing through a resistance is the probable source of that heat.  The normal current flowing at this location should not produce enough heat to cause problems.  So we are looking for excessive current, probably caused by some sort of short circuit.  The most likely reason for a short at this point is a reversed tender truck.  A reversed truck picks up current from one rail, feeds it through the truck screw to the tender wiring, and from there it flows to all the wheels on the opposite track.  The contact between the phosphor bronze axle wiper and the center screw is not perfect.  The amount of heat the current produces at this point depends on the resistance of the contract between wiper and screw.  With a five amp booster, it can be as high as 75 watts.

Initially a locomotive with a reversed tender truck may run just fine.  The resistance between the wipers and the axles is enough to limit the short circuit current to an acceptable value, often a fraction of an amp.  But as the wipers wear in, the resistance drops.  The contact is also initially intermittent, that is, the short circuit occurs only intermittently.  With a dc power pack, short circuits of limited duration go unnoticed, unless you happen to have an ammeter in the circuit.  But add a decoder and run the locomotive on DCC and the results are different.  A momentary short circuit will often shut down the booster for a second or two, which does have a large effect on the locomotive.  And the larger short circuit current will often cause the wipers to wear in faster.

A different possibility is a short circuit between the positive (blue wire) lighting output of the motor decoder and the locomotive chassis, wheels or motor.  This would draw extra current through two of the diodes in the bridge rectifier in the decoder, and probably destroy one or both of them instantly.  These diodes would most likely fail to a shorted condition rather than to an open circuit.  Such a short would effectively connect the red and black decoder wires together.  Such a short would be low resistance although not necessarily a dead short.  It could, however, carry enough current to melt the plastic around a truck screw if that screw were in the return path to the rails.  The destruction of the diodes in a case like this can be so fast that they do not leave a burn mark on any shrink tubing around the decoder.  Testing the decoder in a decoder tester or in a known good locomotive would confirm or rule out this scenario.

[shawneehawk]

Jim, thanks for the input.  I examined the tender trucks again and they were in what I believe to be the correct position...looking down, the front truck wheels are insulated on the left,  and the rear truck wheels are insulated on the right.

As far as the decoder goes, I removed the Tsunami almost 2 weeks ago when it became clear the loco had DC issues.  I put the jumper plug back in the tender and have been trying to get this loco running correctly on DC first before proceeding with DCC.

I could find no solder bridges on the PC board, but am wondering if the problem has been the board itself?

[Jim Banner]

Shawneehawk, I have been assuming that your problem has to do with a short circuit as opposed to an open circuit.  But I am not at all convinced that all readers, or even all posters, know what the difference is.  So for the large number of readers who are following this thread, perhaps you will allow me to explain the difference:  (anyone already knowing the difference can skip to the double dashed line below)

Both open circuits and short circuits can stop locomotives dead in their tracks (pun intended.)  But how they stop it, and how they affect locomotive and passenger car lights drawing power from the same source, are quite different.

In general, an open circuit cuts off power to the motor (and maybe the lights) in a locomotive.  An example is seeing the headlights flicker as a locomotive runs down a dirty track.  The lights go off when all of the wheels on at least one side of the locomotive (and maybe the tender) lose contact with their rail all at the same time, creating an open circuit.  The lights come back on when one or more wheels on both sides remake contact with their rails.  Open circuits at other places on the railroad can also stop a locomotive.  These open circuits could be cause by, for example, loss of contact where the locomotive picks up power from its own wheels, loss of contact at one or more rail joiners, loss of contact within turnouts, loss of contact at the power pack or booster terminals, and so forth.  Some times, we even use open circuits on purpose - an example would be an on/off toggle switch to isolate a storage siding.

Open circuits rarely cause heating, and when they do, it is minor because there are still things in the circuit to limit the current flow, like lights and motors.  An open circuit that causes a locomotive to stop at one place on the layout will often show up as an increased brightness in passenger car lights when the passenger car is parked at another place on the layout, and/or it will cause a GOW bulb connected across the output of the power pack or booster to glow brighter when the open circuit occurs.  The only exception would be if the open circuit occurs inside the power pack/booster or in the wiring between it and the GOW bulb.  An open circuit inside the locomotive can shut off just the headlight or just the motor or it can shut off both, depending on where in the wiring it occurs.

A short circuit creates a conductive path around some place where the electric current is expected to do some work.  Kind of like a dog doing an end run around a hoop because it is easier or it is a shorter path than jumping through it.  Maybe calling it a "shorter circuit" would make more sense, but "short circuit" is already used universally.   Because it does not have to do any work, more electric current can flow than should flow when there is a short circuit.  This extra current can produce heat, often enough heat to melt things or destroy circuits like decoders on sound system.  The extra current is often high enough to shut down the over current device built into power packs and booster for their (and your) protection, but not always.  If the short circuit has some resistance to limit the extra current, it can still stop your locomotive by diverting current away from it yet still not shut down your power source.  This is often referred to as a "partial short."  A short circuit that can and does shut down the power source is often referred to as a "dead short," I suppose because it makes everything go dead. 

A short circuit at one place on the layout will often dim passenger car lights or a GOW bulb wired across the power source.  It will never make these lights brighter.  A short in a locomotive will almost always stop the motor and the lights, except for some DCC cases where the decoder will disconnect a shorted motor without affecting the lights.  A momentary short circuit, such as one caused by a long steamers going through a turnout, often causes little more than a momentary blink of the steamer's headlight when running along on dc but may blink every track powered light on the layout when running on DCC.

Understanding the difference between open circuits and short circuits can make a world of difference when trying to figure out why a balky locomotive or a balky layout refuses to work properly.

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Whew!  If you waded through all that verbiage, then good for you.  If you didn't have to, then good for you too.

Now to the case in point.   It would be really helpful if we knew whether the problem was in the tender trucks or in the adapter board or in the locomotive.  As a first step, Shawneehawk, you could set the tender on the tracks with a piece of paper under the wheels to insulate them from the rails.  Then try to run the locomotive on dc.  If it does not run then the problem is in the locomotive or the adapter board or somewhere between the two.  If it does run, then the problem is in the tender, not in the locomotive.   Try the next two test to see if the problem is in the truck(s) or the circuit board.

To melt the plastic around the truck screw, there had to be heat, and lots of it.  This sure sounds like a short circuit, not an open one.  Shawneehawk, you mentioned in your first post that there were a lot of sparks off the lead tender truck.  This is another indication of a short circuit, particularly one involving that truck.  If the problem is a short circuit, the current is most likely being picked up by the lead tender truck and delivered somewhere.  So why not cut out that little game right quick with a pair of side cutters.  If you trace the wire from the lead tender truck to the adapter board in the tender, you will know which wire to cut to interrupt that lead truck's current flow.  I suggest cutting it about 1/2" away from the circuit board so that you can later find it and have enough to join back up if you need to.  If the locomotive still won't run on dc, then cut the wire from the trailing tender wheels in the same way.  If it still won't run on dc, then it is time to get serious and get rid of the adapter board.  We can cover that, and a few test to do before taking that step, in a future post. 

[shawneehawk]

Jim, I certainly do appreciate your post, and those posts of the others who have tried to help me.  I did perform your first test by placing a piece of paper under the tender wheels and applied DC power.  The locomotive did run, so we know the problem is in the tender or board.  It is too late for me to start snipping and soldering wires tonight, so I'll pick it back up tomorrow.

Observations:  the wiper on the front tender truck is damaged, and will have to be replaced...will probably have to get the whole truck assembly.  Also, I noted earlier that there was one brass washer on the back truck, but none on the front...don't know if this could be part of the problem or not.  I'm tempted to send it back to Bachman and let them figure it out, and may ultimately have to do that, but I am learning a few things.

Other observations:  I got out my only other Spectrum, a 2-10-0 (which will also need converted to sound some day), and looked at the tender trucks.  The wheels are insulated in the opposite order as my 2-8-0.  Don't know if that means anything or not.  Then I looked at one of my BLI mikes, and found the tender wheel insulation matched my Spectrum 2-8-0.