Kriss Motorcycle Products

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Analysis of those things that cause damage to our circuit board.

The results shown in the examples below are very simple to evaluate as soon as a technician inspects the circuit. The diagnosis in this autopsy cannot be more definite! It's simple indisputable and revealing engineering science.

We as the manufacturer make all determination of damage and cause. We do not accept assessments from untrained persons outside our company or someone who didn't realize his mistake and thus insists it was connected properly. If it's connected properly it won't burn up.

Most everyone is familiar with the circuit breaker in their home. It just sits and carries electricity. It's designed to interrupt the flow when current exceeds it's rating. It doesn't open on it's own when operating within its limits or when sitting with no current flow.

If powered up correctly, not reverse polarity, the mosfets and other components in our circuit simply sit and wait for something external to be connected to the output wires. The components don't short, overload or reverse connect themselves. Damage is normally caused from external sources such as overload which includes a short circuit. Water accumulating inside of the box creates a tragic death for any circuit board.

Nowadays, it's not often that someone tries to convince us their mistake was a faulty device.

Reverse Polarity Connections
This suppression diode can only be blown from one of the two causes.	1. Reverse polarity - When one of our units is connected with the power and ground wires reversed a typical reverse polarity situation occurs and shorts out the "Reverse polarity diode" that's installed to help protect the circuit board from suffering catastrophic destruction. After this occurrence connecting the unit, even in the correct direction, will blow the fuse in the motorcycle circuit where the unit is being connected. This design protects the circuit board in most cases. We can identify this circumstance very quickly by removing the shorted diode which then allows the unit to function correctly. The component should be replaced to offer continued protection. 2. Excessive voltage - If the unit was installed correctly and didn't suffer reverse polarity and the unit has been working fine for an extended period of time and then blew it would indicate that there is a problem within the bikes electrical system that's caused an over voltage (above 18 volts) situation or transient high voltage spike in the circuit. These are usually due to a faulty alternator/voltage regulator. The component can be replaced but until the voltage regulation problem is fixed it's likely the diode will blow again.

MOSFET DESTRUCTION (Metal-oxide semiconductor field effect transistor)
These are the components that control switching of power to the lights or accessory.

The Mosfets we use have positive voltage applied to the input side and are controlled by a positive signal applied to what's called the gate to turn off the positive output. Since negative voltage isn't applied to the Mosfet it's not possible for it to short circuit itself. The device simply acts like a switch that sits and waits for something to be connected so it doesn't short out internally on it's own resulting in the kinds physical damage shown below.

A mosfet will be either OFF or ON (saturated). It simply waits for a load to be connected. If the load is too great or negative is connected to either side of the device then it will burn up.

Results of a minor short circuit during installation

The upper mosfet is in good condition.
The lower mosfet has the top blown off.

When the Mosfet device is connected and is subjected to an excessive amount of current flow in a very short period of time, due to a simple short circuit in the external wiring, the component blows apart. The Mosfets we use are normally ON and turned off only when needed so in most cases the Mosfet will not turn off any longer after this kind of failure and the light remains ON steady. Overload from the use of a larger bulb than the Mosfet is rated can result in cumulative heat damage.

If a mosfet does fail due to an internal fault, like static electricity damage, it will simply remain ON and there will not be any signs of physical damage. Physical damage to a mosfet always reveals that it was subjected to external forces beyond it's design capabilities.

Result from reversing the in and out connections

Heat melted the solder and the
lower Mosfet fell off of the small

solder pads on the circuit board.

When the Mosfet is connected backwards (in and out are reversed) the internal structure will permit current flow by what's called the intrinsic diode. The light or bulb being powered will come on for a period because the current is flowing uncontrolled and then go off after the Mosfet is burned up. The Mosfet will heat up significantly, during the reverse current flow and burn up (disintegration) because of the high heat accumulation. The generated heat is usually significant enough to damage the circuit board and the pads that the Mosfets were sitting on. If it's during daytime conditions and modulating has been activated it may or may not actually modulate as the gate is trying to permit current flow across the source and drain but it's not in the proper direction.

This failure is difficult to differentiate from a failed ground because of the heat destruction.

Results of no ground connection

When the ground connection is overlooked or comes loose the Mosfets go into a high speed oscillation because the gate doesn't know what state to be due to the microprocessor is not providing a hard turn on or turn off. This generates excessive heat and the mosfet will burn up in anywhere from a few seconds to minutes. If it's a headlight modulator and the unit is not in the modulation state the lamp will be less bright than normal. If it's during daytime conditions and modulating has been activated then it may take longer to burn up because there is partial turn on and turn off of the gate which delays the heat accumulation.

Connecting the ground to the metal part of the headlight is not a guarantee that a good ground is provided since headlight is often installed using rubber shock mounts or in the case of a plastic fairing there is not any direct ground. The best method of determining a good ground is with a test light or volt meter.

This failure is difficult to differentiate from a reverse connection because of the heat destruction.

Closer view
	Reverse connection and lack of ground are the most catastrophic type of failures.
When a Gold Wing connections aren't made properly.

Above is what happens when a Gold Wing high beam interconnect between the bulbs is wired behind the headlights without using good electrical connection procedures and one of the wires comes loose and then contacts the frame. One gigantic short circuit which destroys the circuit board. We don't replace a unit under warranty when we find this kind of damage. Some people prefer to take the easier route rather than wire as we suggest. Sure our recommended procedure takes longer but then it last a whole lot longer. In our opinion it's not the best to do wiring between the headlights and the instrument panel when you can't see what you're doing.

If we find any damage like that shown above we will not be able to repair the device and it will not be covered under warranty.

If we inspect a unit and cannot see any visible damage or identify a cause of
failure then it will be repaired free of charge if still under the warranty period.