Common faults on the Pro-120 series are - not common. So a full fault finding chart is not a practical proposition. But there are a few faults which occur, mainly because the 'bare board' style of the controller makes it susceptible to certain abuses.
The intention was to update this page slowly as users show the need for assistance. The fact is that the controllers are generally so well behaved that relevant problems are rare!
You may find it helpful to identify the issue number of the controller.
This is a normal symptom of the High Pedal Lockout operating properly because of an external fault. So it usually indicates a mechanical fault causing the throttle pot not to return to zero.
See Ignition relay won't stay pulled in
This sort of fault is only likely to happen on model locos, especially where double heading.
Theoretically, if the wiring was bad such that the pot reference (pin F of the 6 way connector) was connected to chassis, an earth current could flow through pin F. This will probably blow the fuse track to this pin. If this fault happened, the pot would still find its reference through the faulty earth - but the current in this earth is putting a voltage on the bottom of the pot (which is what caused the fuse track to blow). Under these circumstances, the High Pedal Lockout could quite possibly detect this spurious earth signal as the pot not being zeroed.
See Ignition relay won't stay pulled in
Be warned that replacing blown MOSFETs in a Pro-120 is not an easy task and requires skill! It is easy to damage the board, by removing the through hole plating and by stripping top-side gate tracks.
Smell the controller: failed controllers usually have a noticeable burnt smell where MOSFETs have blown. Otherwise problem is usually a dud pot or pot wiring, or the HPLO is detecting a fault and operating!
This turning off of the power relay will cause a significant drop in the voltage on pin A and the pot voltage will fall only slowly as a consequence of this drop.
It is just possible that some other fault is turning off the power relay as the pot is advanced, but this is less likely and other symptoms will usually be present. Disconnect the parking brake and motor to make this test more positive.
We use and recommend these crimp connectors because they are reliable. The F-type crimps we supply require a special (expensive) tool and it is nearly impossible to operate this so as to make a bad crimp. However the commonly-available, yellow-insulated crimps are of variable manufacture and many different tools are available, most of which can give a bad crimp.
Solder is a high resistance material and is must be used very carefully if it is carrying high current. Not suitable for connections of this type.
Screw connections are subject to variable tightening and mechanical irregularity. Bolting to a circuit board is therefore problematical.
A properly crimped connection is 'gas-tight' - the strands of wires are deformed and squeezed into hexagonal cross section. All the air between the strands is excluded and the metal of the stands forms a pressure weld, making an extremely good and reliable joint.
Properly crimped connections are very reliable and the push-on connections are very good if properly made so overheating here always indicates the connections are bad.
Badly made crimps let air at the strands of the wires, which oxidise over time and the joint resistance increases. As they degrade, they start to get hot - which accelerates the degradation. In extremes, this heat can be transferred to the circuit board terminal and we have seen about two cases where the circuit board was actually burned as a result.
Every time a push-on connector is removed and re-made, the springiness of the connector relaxes a little. So is a connector is removed too many times, the contact resistance increases and this can cause heating.
The effect is heavily exacerbated if there is any sideways pressure on the connector: maybe the wire is too short and is pulling continuously at the connector.
Note: the controller may not reverse properly if there is no motor connected (i.e. the output is open circuit): it requires some sort of load (resistor or motor) or the highside current limit engages and prevents correct operation.
This indicates the trouble is in the switch of wiring, and not in the controller. The reversing signal is not getting to the controller.
Check the voltage on pin C of the 6 way connector (black wire) - it should change from zero (forward) to full battery (reverse). It it's not doing this then the switch of wiring is faulty.
There is a signal on the reverse line which the reverse switch is not removing.
Measure the voltage on pin C of the 6 way connector (black wire). When forward is selected this should be zero volts. If not zero, than a voltage above approximately 6.5v will engage reverse.
Usually this means the controller is working but the gain is set too low. On a standard controller, reverse is at half of forward speed. If the gain is set low, forward speed is low and half of this low forward speed may not be enough tom get the motor moving.
Another theoretical possibility is that there the relay contacts are dirty. However these relays used do have high contact pressure and tend to be self cleaning as a bad contact will, initially, get hot - which clears the problem before it shows up.
A relay could be stuck in the de-energised state. Or it could be stuck in the energised state.
Usually such welding is minor (it is called a micro-weld) and a sharp tap with a screwdriver handle, on the cover of the affected relay is sufficient to release the weld.
This would imply that there is a fault in the reversing switch or the reversing logic on the board.
Half speed reverse will not disengage
Sorry about this - you've spotted a manufacturing defect. We don't make many, but we are only human! The half speed reverse must disengage if the link is properly broken. It follows that removing the header is not breaking the link. So look for a solder bridge across the appropriate pins.
With issue 9 (see Issue number history) the parking brake driver is protected against faults in the parking brake wiring.
This protection will cause the controller to switch itself off as soon as the parking brake is released (as the throttle is engaged) if there is a fault.
So unplug the parking brake, disengage it mechanically and, if the machine now functions, the parking brake or its wiring is faulty and the controller is simply reacting to this.
Controller will operate with wheels off the ground but gives no power
Controllers never fade away. When they die, they go usually with a bang and fail completely. Lack of power is always a battery or wiring problem! You need to measure the battery to properly see what is happening. A batter condition meter, if fitted, measures the battery - but is switched on and off by the Pro-120's power relay so only what it measures before this happens is useful.
The Pro-120 does not have battery discharge protection: this can however be engaged, see the instruction manual. However if the battery voltage falls too low, the Pro-120 will turn power down to avoid the relays disengaging. So with a normal dead or discharged battery the voltage should fall to about 15v but no lower and the controller's relays should not disengage.
Not all batteries fail gracefully, Sometimes a battery fails (usually a single cell) such that, above a certain current, the battery voltage suddenly falls very low - in effect the cell suddenly switches open-circuit. This is too sudden for the Pro-s undervoltage to work and the power relay will disengage.
Either of these effects could also be caused by bad connections or wiring to the batteries.
If all the wiring is good and the controller is pushed to the limit, it will overheat. Although there is an overheat sensor fitted, there is actually no single point that gets predictably hottest first, so measuring only one 'hot-spot- is not perfect, but it would not be possible to monitor all possible points that can get hot.
It is quite possible for the controller to get so hot that the solder melts. This can happen well before any electrical failure, but once the solder melts it will run and cause a problem.
If the controller is overheating, it indicates that it is in fact working properly and that the system is simply asking too much of the controller.
Legitimate overheating may show up in several ways:
Ignition relay won't stay pulled in
See above under 'Controller is dead'.
As explained in Pro, Scoota and NCC series controllers internal power supply and protection circuitry, the 9v rail's presence is used to power up the ignition relay.
The ignition relay will fail to power up properly under the following fault conditions:
If you do not allow enough time between connecting the battery and switching on the ignition - the capacitors will not have charged up. This is particularly so on the 48v controller.
This indicates either an internal fault - or are you trying to power something other than a pot (min value 5K) from the pot supply? Pinch more than a couple of milliamps from the 9v line and the controller will detect a fault. The internal current consumption varies with the speed, the battery voltage and other factors such as temperature, so this fault could show up erratically.
Make sure that the throttle control is returning properly to zero. If HPLO is inappropriate to you, then the manual explains how to deactivate it.
If the battery voltage falls low enough, any relay will drop out. The Pro-120 series have under-voltage cutback which prevents this. As supplied, the level on the 24v controllers is around 15 volts, enough that the relays will hold. However - cutback is disabled on the 12v controllers.
However - if the voltage dip is causes by something other than the controller, then there is nothing the controller can do to prevent the dip and, if it dips too low, the relays will indeed drop out.
Even if the controller catches itself - such a dip does mean that the batteries and/or wiring are inadequate to give the current required. There's nothing the controller can do about that!
This probably is not a controller fault. Controllers either work properly - or they fail. For a controller to partially fail is almost unknown.
If you push a Pro-120 hard, one of two things happens:
Has the system just been setup or is it a system that worked properly once, and has failed?
Best advice is to use our on-site current calculator and work out what you are asking of the machine.
If you are really push a controller too hard, it overheats. There is a separate section on overheating.
Almost invariably, this indicates trouble in the batteries or the battery wiring.
Is there any sign of anything getting hot? See overheating.
If there is a battery condition meter fitted, does it show that the battery voltage is dropping? The condition meter, to be useful, must show the voltage inside the controller, i.e. it must be fitted to plug into the 6 way connector, as described in the instruction manual.
If you are measuring with a separate meter, compare the voltage in the hand controls with that across the battery. Any difference between he two must be dropped in the wiring or the connectors.