The Train Doctor


The information on these pages comprises a few (hopefully) helpful hints, maintenance tips, and other technical bits and pieces gleaned mostly through my own experience. 

There are also some items that have come from various pieces of documentation that the hobbyist should have seen, but may not have, especially where equipment has been purchased second hand and original instructions etc have been lost.

And the inevitable disclaimer: If I'm working on your loco it's my risk.  If you're working on anyone's loco, whether or not you're following my hints, tips, or other advice, and whether or not your Preiserlings are sitting on your shoulder directing your every move, it's all your risk.  








Page 1.  General

Lubrication .............The perils of excess.

Wheels & Tyres ....Be careful you don't "turn a wheel" when changing tyres.

Pick-up Shoes ........How to set them up properly.

Field Coil Leads ....How to avoid breaking them off.

The "light pipes".....Don't glue the lichtkörpers in.

The 7072 control boxes....Boxes "warped" - buttons sticking? A cure perhaps.

Wiring Diagram for a simple analogue loco....not sure where that wire came from? This might help.

Intermittent Running ......Loco stopping all over the place? What to do about intermittent power loss to your loco

The 7186 Turntable ........Hints and Schematic.

Transition Curves in C track  ........  Have a wide radius "lead in" to your main line curves.


Page 2.  Digital

Old Transformers ..A warning if you're using these to run digital locomotives.

Analogue/Digital Switching.... Another warning if you're switching back and forth from analogue to digital control

Decoder Leads ......How to stop the wire leads falling off decoders

Address Table for DIP Switch equipped decoders ....If you're DIY-ing

Decoder Wiring Colours  The standard Märklin decoder wire colours and their DCC equivalents

Decoder wiring harness...... Where the wire came from on that decoder.

Lost MFX Locos.....A work-around for when your MFX Loco won't register or disappears from your Central Station.






























Being in the repair business, I see quite a few problems which have been caused one way or the other by insufficient care, too much care, or the wrong sort of care.  If you really don't want to send your loco to me (or anyone else) to have it repaired, here's some simple tips on what to do, and more importantly what to not do if you want to avoid some of the most common problems. 


Don't over oil.  Too much oil causes more problems than not enough. You'll generally be able to hear if your loco needs oiling, and in most cases with standard Märklin motors, a single small drop on the armature bearings is going to be all that's required. You may also need to put a small amount of lubricant on the gear spindles and teeth, but for the usual amount of running a loco gets, you probably won't have to do this more than once or twice a year at most.   Too much oil on the wheel bearings and gears attracts dirt, dust, lint, cat hair, Preiserling litter (they're a messy lot) and other sundry nasties. This makes a sticky mess that gets all over everything, and needs some work to remove before re-lubricating properly. 


Worse still, excess oil can migrate to the commutator.  The oil softens the carbon motor brushes, combines with the carbon that comes from the brushes and forms a sticky semi-conductive paste which lives and breeds in the gap between the commutator segments. This causes a partial short circuit that results in excess current draw and lethargic running. That's on a good day - on a bad day with digital locomotives, it'll overheat the motor output drivers and cause the loco to stop suddenly for no apparent reason until things cool down again.  I haven't actually seen this cause a decoder to burn out, but it could be possible.


Excess oil will also cause the rubber tyres on your loco to stretch and fall off way before they're worn out.


What oil to use?   I recommend and use the Labelle range (no vested interest), which includes some plastic-compatible lubricants for use on nylon gears.  On locos with a worm drive, I use a teflon grease rather than oil on the worm, and the same grease can be used on older locos with worn gear teeth to help quieten things down a bit.   For the casual owner with just a few locos that get an average amount of use, there's really nothing much wrong with a good quality sewing machine oil.   Don't use salad or vegetable oils.




Wheels & Tyres 

I'm sure you'll know if you have to change a tyre on a loco - maybe you've just faced a deputation of your Preiserlings complaining about a broken tyre lying in the middle of their recreation reserve.  No great drama or special technique required in changing a tyre, but for steam locos (or any locos with side rods) you're going to have to undo the coupling rod retaining screw to be able to put the new tyre on.  Still no problem, but.......  When you're tightening this crank screw up again, always hold the wheel on which you're tightening the screw, NEVER its opposite number.  If you hold the opposing wheel, you can cause wheel slip on the axle, and on steam locos this can have serious consequences: - the wheel cranks get out of synchronisation with each other and the result is binding of the mechanism caused by the coupling rod mis-alignment


For the same reason, one should NEVER force-turn the wheel of a loco by hand unless the brushes are removed and the mechanism is all free and easy.


On older locos that have gear drive to all wheels, if the wheel hasn't been loosened on the axle too much by the turning, the correct wheel position can be gauged by eye and relatively simply reset. 

On locos that actually use the coupling rods to drive the wheels, wheel slip on the axle places one suddenly into real disaster territory: The wheel "quartering" needs to be exact or the whole mechanism will lock up, and on a bad day coupling rods can get bent. Usually, simply putting the wheels back in the correct rotational position isn't going to be a help for long either, because once the wheels have turned on the axles, they become loose and keep shifting for ever and a day until re-set and re-fixed properly. 


If your steam engine makes a sort of wump-wump-wump noise as it heads off down the track at speed (beware the Preiserling noise abatement society), it's probable that the wheel cranks are slightly out of alignment.  On digital locos the effect is worsened because the decoder tries to compensate for the rotational binding by applying more power to the motor, unfortunately, by the time it does so it's too late, the mechanism has moved past the tight spot, and the extra power is not needed. This can result in speed surges at certain speeds, and uneven running.


Having digested that, it follows then that removing the wheels on a loco is an amusement to be avoided if at all possible.  As well as the problem with wheel quartering & coupling rod synchronisation, one encounters the difficulty of pressing the wheels accurately and squarely back on to the axle:  If the wheels are not exactly perpendicular to the axle and set at the correct back to back spacing, one's loco will waddle down the track like a duck or fall off the rails with the slightest provocation. The larger the wheel, the worse the problem.  The aforementioned Preiserlings might not mind the wobbling, (after all they won't get bounced about, they're safe in a coach 3 back from the engine) but they will be less amused if your loco becomes de-railed and falls on its side halfway through a tunnel, spewing ash, smoke, soot and asphyxiating gases all through the tunnel.   While Preiserlings are not widely known to bring law suits against their 87 times over-sized masters, if ever there was a possibility of such, this would be it.


Back to the serious business,  Unless you have the special tools required to accurately achieve the re-assembly tasks, removing the wheels from a loco is not something that should be undertaken without due thought for the consequences.  




Pick-up Shoes

Maybe you’re replacing a pick up shoe on your favourite loco because you’ve just run over one of your Preiserlings with it and neither the Preiserling, nor the shoe can be resuscitated, or perhaps the shoe is noisy, is giving bad contact or creating spurious short circuits.
Whatever, if the shoe wants attention you’ll probably need to take it off to make a decent job of rescuing it. (Or perhaps you’ve really lashed out and bought some new shoes from your favourite Train Doctor?)
Well before screwing the shoe back in place, what about giving things a check-over while you’re at it? First of all, if it’s an old shoe, make sure the springs aren’t creased and munted. If they are chuck it out, it’s not worth trying to maintain correct tension on creased pick up springs.
Next, check the underside of your shoe. It should be straight and flat (not concave or convex). Lay the edge of a steel rule against it and look at it in good light. Even new, out of the box they’re often a bit out. Fix that while you’ve got it in your hand.
Now screw the shoe on, making sure that it’s in a direct line parallel with the chassis (not at an angle across it) lest the leading edge of the pick-up shoe catches between centre stud and guide rail on points etc. On sharp curves with the longer shoes I’ve even seen the leading edge drop between stud and running rail.
Next, adjust the tension on the leaf springs. In the days when they cared about such things, the diagrams Märklin used to put in their handbooks showed the shoe hanging about 2mm below the wheel flange: - that’s probably about right. Too much enthusiasm with the pick up tension will cause the shoe to be noisy and clatter over the studs as the leading and trailing edges alternately hit and fall off the studs. On small, light locos excess tension can also take weight off the wheels, causing lack of good electrical return through the running rails and loss of traction. To adjust the tension, I use a small pair of long nose pliers with a wee right angle at the tip, a truly marvelous tool. Increase or decrease tension by bending the spring right where it leaves the base. Adjust so that the shoe hangs at that 2mm below the wheel flanges, and ensure it hangs evenly (not up or down hill). Failure to observe the latter will also cause shoe “clatter” and excess wear.
Just one more thing: If after all the effort getting things adjusted and set up correctly, your Preiserlings are still grizzling about intermittent running (ungrateful lot), it could be that there is bad electrical contact caused by a build up of gunge in the little up-turn loop thingies where the pick-up spring meets the ski piece. Put a drop or 2 of cleaner/grease solvent in that loop at each end, and tap the bottom of the shoe to work it up and down a few times. That can perform miracles for bad pick-up problems.





Watch those coil leads

The leads from the field coil on older analogue locomotives are often just a continuation of the field winding itself that has been sleeved with a piece of insulated tubing.  Over several years that tubing gets hard and brittle, but even where it hasn't, it's pretty easy to break off that lead.   Also, At the centre tap of the coil, 2 wires come out together and are generally wired directly to one of the motor brush leads.  It's pretty easy when one is working around that area to break off a coil lead and especially with the centre tap leads, loose the end of it in the winding and thus not be able to repair it easily.      A few "things":

Thing 1:  I usually put a dob of hot melt glue at the point where the wires leave the coil. This prevents the wire breaking so close to the coil that one can't retrieve the end

Thing 2: Never be lazy and try and remove the brush plate without un-soldering the wire leads first - you'll be bound to break the field coil leads, probably up against the field coil itself where you can't get at it.

Thing 3: With regard to the long flying leads on the older coils, I sometimes take the old brittle insulating tubing right off, thread the end of the wire lead through the hole in the former where the wire comes from (wind it round as many times as the length of wire will allow), clean off the upper surface of the resultant windings so that one can solder to them (fine emery paper), then solder on a piece of fine flexible stranded wire to enable the connection to the reversing switch (or wherever).   Just be careful here because the soldering iron will melt the plastic former, so you need to have the temperature set fairly low, and get in and out with the iron as quick as you can. 





Head lamp light conductors on your steamers


Several of the "big" steam locos (BR01, BR03 etc) have light-conductors in the form of a "y" piece that sit in a groove at the front of the loco chassis. These conduct the light from the light bulb itself out to the "lamps" mounted on the front platform of the loco.  If the loco body is removed there is little or nothing preventing this "lichtkörper" (german word)from falling out on to the floor or workbench.  If you're thinking about gluing it in place, note that a lot of plastic glues, superglue etc, will etch into the surface of the lichtkörper.  This roughens the surface and will allow light to escape instead of being reflected back into the "pipe".  The result is dim lower headlamps.  You might try a wee bit of double sided sticky tape to hold it down instead.

Be careful handling the lichtkörper as well.  If it gets scratched about too much the same result will follow.







Have those old blue control boxes about had their day?


The old 7072 push button boxes that are meant to control your points, signals etc have an almost universal habit of warping after a few years with the result that the buttons stick, and they function only intermittently (if at all).

I've had a modicum of success repairing them by removing the tops, buttons etc, and warming the body of the unit with a heat gun, while applying pressure to straighten them out.  WARNING - warm them slowly and carefully and don't let them get too hot!: - There is a temperature point at which they very suddenly turn to a soft play-dough consistency and if you're not careful you'll finish up throwing the whole thing away.  In a "nothing to loose" frame of mind though, I successfully brought back from the dead 4 out of 5 boxes that I'd had lying in my junk box for several years.





Wiring diagram for a simple analogue engine (3000 etc)


Not sure where that wire came from?  The following diagram may help.  This diagram is for the 3000, but virtually all the analogue locos are wired to the same generic scheme.




































What to do about intermittent running / Loss of Power


I often get asked about how to cure intermittent power loss in locos.  Now the answer to this might seem pretty obvious: Clean the Wheels, Track, and Pick-up Shoe,  but it isn't always as easy as that.  Often the problem occurs when a loco which used to run ok in analogue mode suddenly starts stalling on the track after conversion from analogue to digital.  In fact maybe this article ought to appear in the "digital"  section because it does affect digital locos more, but then again it isn't really a digital problem so....aah well, I had to put it somewhere.


The reason that digital locos suffer more from intermittent power loss is that they have a Direct Current Motor.  An A.C. motor with field windings will often coast quite well over un-noticed dead spots on the track because when power is lost to the armature, it is also lost to the field coils, the magnetic field collapses, the motor is free to turn and the loco will “coast”.  Once the digital conversion is done however, and the field coils are replaced by a permanent magnet motor, momentary power loss will cause the armature to be “grabbed” by the powerful permanent magnetic field and it stops dead.  i.e. there is very little coasting ability.


For the purpose of this article I've assumed that the problem is indeed a power pick-up or return problem and not a wiring or other problem within the loco itself, (which may well be the case) because I had to define the bounds of the article somewhere.  As a guide if the lamps in the loco go out at the same time as the loco stalls, then it probably is an external problem.  If the loco lamps stay on, then it certainly isn't so that will have to be addressed in some other article


What to do:  First, do make sure that wheels and pick up shoe really are clean as mentioned at the start of this article and that the track is free of squashed Preiserlings or other non-conductive nasties.  If those things appear ok then we need to ascertain whether we have a wheel contact problem or a pick-up problem.   Run the loco slowly over the track until you find a point where it actually stops.  Take a short length of wire or clip lead, hold one end on a good ground (rails) and touch the other end on the wheels or chassis of the loco.  If the loco moves off, then you’ve got a grounding problem to get to the bottom of.   If the loco still doesn’t move, then hold one end of the wire on the track power source and touch the other end to the pick-up  (This latter is sometimes pretty difficult to do without causing shorts,  and it may prove easier to remove the loco body and touch the  “hot” wire on an internal point somewhere e.g. the overhead/pick-up selector switch if your loco has one, BUT, if this is a digital loco, be *VERY* careful here: If you touch that hot wire on the wrong place it could be disastrous for the health of your decoder - I can take no responsibility for this)  Sometimes one can simply press on the pickup or move it slightly with a pencil or such to prove the point.


If the above testing points to a Pick-up shoe problem:   First, make sure the pick-up shoe is adjusted correctly and is clean.  The skate piece of the pickup should be perfectly flat (check with a straightedge) or perhaps *very slightly* concave.  Definitely not convex.    There should be reasonable tension on the pick-up shoe springs, but note that too much tension can cause problems with small locos because it tends to take weight off the wheels, thereby causing loss of traction and degrading of electrical conductivity back to the running rails.

I have seen problems with pick-up shoes on occasion where the leaf spring doesn’t make decent electrical contact with the skate of the shoe. Try putting a little grease solvent, (white spirits or whatever you use) into the “turned up loop” at each end of the pick-up skate where the leaf spring makes contact, and work the pick-up up and down a few times.  That normally cleans it out ok. 



Wheel/Ground return problem: 

For electric and diesel locos with a flat chassis and bogies at each end, (e.g. V200 diesel,  BR141 elok  etc) I always run a grounding wire between the frame of the front (idler) bogie and the ground point on the chassis, whenever I do a digital conversion.  (One needs to remove the bogie to clean a piece of its frame and solder the wire to it).   I run the decoder ground wire to this same chassis ground point, and also bond it to the earth lug on the motor chassis.   All 3 mechanical components are now bonded together and this should ensure good return contact.  A single wire from decoder to motor block will seldom do the job properly with any pivoting bogie type of loco.

The same applies to any pivoting chassis type locos.  e.g Swiss crocodile or the old BR44 with 2 part chassis etc: Make sure all  chassis sections and the decoder ground are bonded together electrically.


Hopefully, the above, which covers most the "common" points power contact faults will help resolve your problems


On digital locos it is possible to overcome intermittent power type problems electrically by the use of capacitors to “back up” the power supply for the decoder.  There might be legitimate reasons for doing this, but I’ve never had to and would consider it only as a very last resort.     It’s really treating the symptoms rather than fixing the cause, and apart from the possibility of blowing your decoder up if you don’t do it right, there are other disadvantages also (like the loco won’t stop promptly at "dead" signal sections or when you cut power in an emergency)