OPERATION - Locomotive Troubleshooting

Overview -

Train operations transition from fun to nightmare quickly when locomotives become balky or stop altogether. This discussion is intended to be a check list of procedures to analyze why a train stops running as desired and how to prevent damage to both the locomotive or other rolling stock and the layout wiring and throttles.

The throttles on the San Diego Model Railroad Club HO layout deliver high current (in excess of 5 amps) and can at times inject upwards of 25 volts into the rails at gaps between blocks. This is sufficient power to permanently damage motors, constant lighting units, and break down wheel insulation. While everyone at some time or other is distracted or confused during operations, it is important, once trouble is detected, to shut off throttles and think while the power is off.

The control panels are currently undergoing modification to install voltage and current metering on each throttle. These meters are extremely valuable troubleshooting tools since most problems result in the train stopping. Another tool at your disposal is the track schematic on the panel face, along with the route control LEDs on turnouts. Assumed, but not always valid, is that the operator understands the relationship between the schematic and actual track blocks on the layout.

Example 1:

A train is heading downhill into a block normally. Suddenly it coasts to a stop in the middle of a block. The current meter for the throttle shows maximum, but the volt meter is very low. The speed control has little effect until turned fully off.

Probable causes:
There is a short circuit somewhere. The most likely cause is a derailment, especially if there is a turnout somewhere under the train. Check the locomotive(s) first, and if nothing seems abnormal, work back through the train for derailments. Pay special attention to metal trucks, brass cars, etc. Look at the schematic. Is there a turnout thrown under the train. This happens very frequently, and will continue to derail cars until fixed.

If everything seems OK, but the trouble persists, are there other trains entering or leaving the division? A train suddenly "showing up" at the division point from the next panel can short out a throttle too. You may be watching one train and see it stop because another train produces a short. Troubleshoot by turning off all blocks on the panel, check the throttle is operating properly, and then test just the block containing the suspect locomotive.

Less common is a short between throttles because of a closed up gap or a failed toggle switch. Failed switch machines on turnouts can also produce a short in one route, but not the other. Again the secret is to shut off blocks to eliminate as much as possible. When testing, bring up the throttle slowly, looking at the meters as well as the train. If still experiencing trouble, SHUT IT OFF AGAIN while you think what to do next.

Example 2:

A train with a single locomotive is travelling normally and then suddenly stops. The current meter for the throttle shows zero, and the volt meter is adjustable with the throttle knob.

Probable causes:
  1. The locomotive has dirty wheels or an electrical pickup problem internally. Tap the top of the locomotive to test this possibility.
  2. The train has entered a dead block (i.e. no throttle selected or the selected throttle is turned off. Since some locomotives need more voltage to keep from stalling, it may be that the throttle is set too low. )
  3. The locomotive is on a turnout frog which has a defective auxiliary contact on the switch machine. If the locomotive is dragged forward a couple inches and starts up again, there should be a bad order form filled out for track/electrical so this can be fixed.
  4. The locomotive is a steam engine and stopped at the division point between two panels. This is a symptom of loss of reference (or common) between the two panels. Note: Although the entire railroad has been converted to common rail this symptom will occur at the division between common rail power supplies and isolated supplies (such as the branch line or narrow gauge).
Since the branch line will never be true common rail at times there may be difficulties getting into or out of the branch line from the rest of the railroad with steam power (or doodle bugs and other equipment with single side pickup on front/rear trucks.)

Example 3:

A train with multiple locomotives suddenly slows down then speeds up again at random intervals. Both the current meter and volt meter for the throttle show nothing abnormal.

Probable causes:
  1. One of the locomotives has either a mechanical problem or internal electrical problem. If you are watching carefully when the train slows down, one set of couplers may be compressed behind the defective unit. If this does not occur, the last unit is likely the one which is dead. The easiest way to check (if time permits) is to uncouple all units and space about a foot apart. Bring up the throttle and see if they all move at approximately the same speed. If one locomotive unit is intermittent, it will show up with this test.
  2. There may be a bad track feeder in a particular section of track. Multiple units will draw more current and consequently be more sensitive to a bad track connection. If this is the cause, most trains will slow down in one particular area but nowhere else. Note: the track detection electronics used at Union Station/Rose Canyon have an inherent 1.5 volt drop through the circuit card. Trains will need slightly more throttle through detected sections of track than normal blocks.

Example 4:

A train will operate properly but is unable to reverse (i.e. always goes forward) when the throttle is reversed. Both the current meter and volt meter for the throttle show nothing abnormal.

Probable causes:
  1. The train is currently in a reverse loop or other reversing section. The direction control while in the loop is a toggle switch on the panel. Be careful reversing in a reverse loop as it is easy to cross out of the loop to a throttle now going the wrong direction.
  2. The throttle direction relay is defective. Try another throttle to test this possibility.
  3. The coil cord or handheld controller is defective. Swap with the other throttle to isolate either the cord or the box. Make sure the “phone” plug is properly seated at BOTH ends and the little wires in the jack are not crunched (visual inspection only). Bad order the whole throttle if unable to isolate to a replaceable part.

Example 5:

A train suddenly surges ahead at high speed. The volt meter for the throttle shows maximum, but the current meter shows normal.

Probable causes:
This is a coil cord or handheld controller problem. Isolate by swapping with another cord or box. Under rare circumstances a broken wire from the controller jack to the power supply or a bad supply can produce this symptom.

Example 6:

A train suddenly surges ahead at high speed. The current meter shows zero but the volt meter for the throttle shows normal.

Probable causes:
The train has transistioned to another throttle (usually another panel) which is set much too high for this particular train. Be careful of override swithes on YOUR panel if all your throttles are off, but the train is still moving at high speed.

Additional Topics -

There are many other obscure problems which may occur, such as problems with direction lighting failures in locomotives, but the examples above are representative of troubles the operator is likely to encounter. Trolley problems are beyond the scope of this guide, although users of the branch line should at least be aware of the 2-rail/trolley programming switches located near the lift out into the reverse loop. Again, learn to think with the throttle turned off, and if in doubt with the panel turned off. Once you form an opinion about the problem, bring up power on the throttle only long enough to test that this is indeed the fault.

For more information about troubleshooting locomotive problems, contact Brian Satterlee or any other members of the electrical crew. Once you learn the nuances of the throttles and how to use the panel meters effectively, you will enjoy operations more and prevent damage to your and other member’s equipment.