OPERATION - Locomotive Troubleshooting
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.
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.
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
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.
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.
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.)
- The locomotive has dirty wheels or an electrical pickup problem internally.
Tap the top of the locomotive to test this possibility.
- 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. )
- 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.
- 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).
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
- 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.
- 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.
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.
- 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.
- The throttle direction relay is defective. Try another throttle to test
- 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.
A train suddenly surges ahead at high speed. The volt meter for the throttle
shows maximum, but the current meter shows normal.
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.
A train suddenly surges ahead at high speed. The current meter shows zero
but the volt meter for the throttle shows normal.
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.