The ignition system of a bike equipped with electronic ignition consists if three major parts: the coil, the ignition trigger (can), and the ignition control unit (often called the ignition amplifier). The coil is usually easy to test, but verifying whether the trigger or the control unit has failed can be a bit more tricky.

Referring to the extract from a wiring diagram one can see that three wires go from the control unit to the ignition module. Two are positive (power - pin 5) and negative (ground - pin 3) power, the third being the trigger wire (pin 6). Each time the trigger goes to ground a spark should be generated in the coil.

Testing the control unit therefore should be as simple as powering the unit up and grounding the trigger wire.

The procedure is as follows:

1) Unplug the connector that connects the harness from the trigger unit to the harness from the control unit. Be careful as there is a small wire spring clip holding the connector together.

2) Remove one plug from the engine, reconnect the ignition wire and lay it on the cylinder such that the plug body is grounded and you can see the spark gap.

3) Stick a pin or fine wire into the center connector of the connector coming from the control unit (the one unplugged in step 1).

4) With the ignition switched on, momentarily ground the pin/wire coming from the center connector. Each time you do this you should get a spark at the spark plug. This will indicate that the control unit is operational.

Do remember however that it is not unheard of for the amplifier (or any other piece of electronics for that matter), to operate perfectly when cold and fail when warm/hot.

The above is copied from a full wiring diagram. Although not drawn in the diagram, the trigger wire (to pin 6 of the unit) really is the center connector..

The ignition can contains a Hall effect sensor, a magnet, and a slotted metal cylinder which rotates between the magnet and the sensor. This causes a voltage on the output pin to vary thereby triggering the input pin of the ignition control unit.

Note the diagram showing how to wire the connector off the bike for testing. The unit is powered from a 9 to 12 volt power supply (battery), and the output from the sensor (center pin) is pulled high through a 10 kilohm resistor. As the shaft on the cannister is rotated, voltage from the center output pin will fluctuate between a few millivolts and V+ (9 to12 volts). If this makes sense to you, go for it. If it doesn't then it might be wise not to invite trouble.

With the unit on the bike, you can test this unit by carefully locating the center wire and connecting the voltmeter between this wire and ground. A useful way to make the connection to the wire is by sticking a pin through the insulation until it makes contact with the wire inside. Be careful that the pin does not touch the engine case. With the engine cranking you should see the voltage on the meter fluctuate at the sensor switches on and off.

Remember that this will not show up intermittent or heat related faults.

Good luck

This diagram should give you all you need to diagnose most basic charging system problems.

Referring to the diagram:

With the ignition on (switch closed) and the engine off current flows from the battery, through the charge light, the voltage regulator and the rotor to ground. This provides the initial excitation (magnetization) to the rotor to get the alternator working when the engine is started. If the rotor is open (broken wire), the brushes worn out, the charge lamp burnt out or some other fault in this circuit, curent will not flow, the charge light will not illuminate and the alternator will not operate correctly.

With the engine on and running fast enough for the alternator to produce a voltage above that of the battery (ie it is charging), the voltage at the B+ and D+ terminals of the diode board are equal. Because of this no current will flow between the D+ and B+ terminals and the charge light will be extinguished.

Current from the B+ terminal will go to charging the battery and current from the D+ terminal will be available (via the voltage regulator) to magnetize the rotor.

As the rpm drops, the alternator will not produce sufficient voltage to charge the battery and the voltage at the D+ terminal will drop below the voltage of the battery. Because the B+ terminal is tied directly to the battery, its voltage will be maintained at battery voltage.

The voltage at the battery is now higher than the D+ voltage and current will therefore flow from the battery through the charge lamp, the voltage regulator and the rotor to ground and the charge lamp will again light.

As the RPM increases the voltage at D+ again increases until it equals battery voltage and the lamp again goes out. When the voltage at the D+ terminal (which is equal to the B+ terminal if the voltage is above the battery voltage) exceeds a specified voltage, the voltage regulator cuts power to the rotor, reducing its magnetism thereby limiting the maximum voltage output from the alternator to a safe value.

From this you can understand the common test for the voltage regulator. Remove the regulator, and short the DF and D+ terminals in the plug. With a voltmeter across the battery, does the voltage increase to 14.5 volts and more as the RPM's are increased? (Stop at 15 volts as damage can result). This test works because the voltage regulator is out of the circuit - remember that the voltage regulator is really a voltage limiter.

R75/5 - Charging light failed, now the starter won't work......

Had a guy phone here hoping I could help with this problem on his R75/5. Basically his starter wouldn't work, and after replacing the starter protection relay, he was preparing to replace the starter and was wondering if we did rebuilds. As it turns out the problem had nothing to do with starters.

Over the phone we checked all the starter circuits with a meter. Most of this can be done from the connections onto the starter relay itself. Here you can check that the starter switch makes contach with ground when pressed, you can trigger the starter motor by shorting the appropriate contacts together etc. Everything checked out and therefore the problem seemed to be the starter protection relay - but he had already replaced that part. He then mentioned that after he had fixed the starter he was going to work on a charging problem. Seems that the charging light was never coming on when the ignition switch was turned on.

Bingo! or is it Eureka?

On the /5, the starter protection relay is supposed to prevent the starter operating accidently with the engine running. (supposed to - in reality it doesn't work very well at idle - read on). It does this by connecting to the charging system at D+ (see the diagram above). Here is senses the voltage and if it is above a certain value it disables the starter circuit.

It works something like this....
With the ignition on and the engine not running, the voltage at D+ is close to zero. This is because there is almost no resistance (a few ohms) across the rotor to ground, but the resistance of the charge light coming from the battery is relatively high. In this state the starter is enabled. With the engine running, the alternator causes the voltage at D+ to reach 12+ volts through the D+ diodes. So as the voltage rises above a certain point (varies from relay to relay) the relay disables the starter circuit. Now, if there is a break in the circuit to ground (ie if the voltage regulator if open circuit, the rotor is open circuit, or even if the brushes are bad), the voltage at D+ (coming through the charge light) will be high (12 volts) and the protection relay will disable the starter.

So we checked out that part of the circuit and did find a bad rotor. To compound the problem, it appeared that the rotor problem was intermittent - the bike would start once, then refuse to crank the next time. When the bike was refusing to crank, a test across the rotor slip rings confirmed an open rotor winding.