Models KH400, KH250, and S series are equipped with a solid state voltage regulator (SVR). This unit consists of a zener diode (ZD), a thyristor (Th), and two resistors, as shown in Figure 26.














KH250 and S Series Troubleshooting


If a malfunction of the solid state voltage regulator is suspected, it may be checked by the following tests. However, bear in mind that if the battery is low, the regulator will not work properly even though it may be in good condi­tion. Therefore, be sure that the battery is in good condition and at or near full charge before attempting to trouble shooting a suspected malfunction.


1.   Measure resistance between the brown wire and the case. Resistance must be greater than 1,000 ohms.


2.   Measure resistance in both directions be­tween terminals 2 and 3. Resistance should be essentially infinite in both directions.


3.   Connect the motorcycle battery to the regulator as shown in Figure 27. Be careful to observe proper polarity. No current should flow in the circuit between terminals 1 and 3. Measure resistance between terminals 2 and 3. Resistance should be essentially infinite.


4.   Connect an additional 4 to 6 volt battery in series with the first battery to make a total of over 16 volts across terminals 1 and 3. If cur­rent does not flow, either the zener diode or the first thyristor is defective.


5.   Replace the regulator if it fails any of the foregoing checks. If its condition is still doubt­ful, check it by trial replacement with a known good unit.








KH400 Troubleshooting


1. Check the resistance between the black and yellow/green leads (Figure 28). Resistance should be between 1,000-1,200 ohms.


2.  Connect the circuit shown in Figure 29 using a suitable power supply. Set the voltmeter to the 30V DC range. Turn on the power supply; the light should be off. Gradually increase the voltage from 8 to 14 volts; if the regulator is good, the bulb will light between 10-12 volts.


3.  Replace the voltage regulator if it fails either of these tests. If its condition is still doubtful, check it by trial replacement with a known good one.


Handling Precautions

Certain precautions must be observed when you handle or service the solid state regulator. Failure to observe these may result in damage to the unit.


1. Be sure that the mounting screws are tight.


2. Always be sure that the main switch is off before connecting or disconnecting the unit.


3. Be sure that the unit is mounted securely.


4. Be sure that the wires are connected prop­erly. Improper wiring will result in damage to the battery and regulator.


5. The battery must be charged to near full capacity for the regulator to work properly. If the battery is very low, charge it before in­stallation.







Some alternators use separately excited field windings. Such alternators require a more com­plex regulator. As engine speed increases, alter­nator output tends to increase. It is possible, however, to control alternator output by con­trolling its field current, which is used for ex­citation.

Figure 30 illustrates the situation at low engine speeds. The rectified alternator output is applied to coil B. However, since the output is low, the magnetic field developed by coil B is too low to open contacts C and C0. Under these conditions, field current is supplied by the battery through the ignition switch, and is at its maximum value.

As alternator output voltage tends to in­crease, coil B develops more magnetic force, which breaks contacts C and C0. Field current is then supplied from the alternator output through resistor C. Resistor C limits the field current, and thereby reduces alternator output so that contacts C, and C0 again close, repeating the cycle.

At high engine speeds and light electrical loads, the action of the upper and center con­tacts is insufficient to control alternator output. As output voltage continues to rise, coil B pulls the movable contact C0 down to the lower con­tact C2. Under this condition the field is grounded, and alternator output drops to zero. As it drops, the movable and lower contacts separate, and the cycle repeats.



Regulator Testing


The most common causes of voltage regulator trouble are open wires or short cir­cuits. To check the regulator, proceed as follows.

1. Remove the regulator.


2. Measure resistance between the brown and black leads (Figure 31). Resistance should be approximately 55 ohms.


3.  Connect a voltmeter across the battery ter­minals. Reconnect the regulator.


4.  Start the engine and run it at 5,000 rpm. If the measured voltage is 14.5 plus or minus 0.5, the regulator is OK.