Topic: CB550 Unknown rectifier- Help identify and how to test it please

[apehanger 550]

  I am trying to sort out a CB 550 with multiple issues with the handle controls. The starter solenoid small wire leads are what operates the internal magnetic coil that causes the magnetic starter switch to operate. One of the leads is yellow/red stripe and the other is green/red stripe.
  There is another green/red stripe wire that connects to a little part that looks like it could be a small two blade rectifier [about 1-1/4 x 3/4 x1/2 inches or so. The "rectifier" has two male prongs at 90 degrees to each other and one of the prongs connects to a green/red stripe wire and the other to a white/red stripe wire. I cannot trace exactly where either wire comes from because the wiring harness is really restricted right there.
  Anyway, the "rectifier" [if that is what it is] has no continuity either direction. For all I know,a continuity test might not even be the way to test this part. The Honda online microfiche parts finder is pretty blurry or I would know what this part is. Possibly it is part # 31700-124-008.
It is mounted right over the top of the voltage regulator in a rubber bracket.
  The information that I need is--1. Did my testing reveal a part needing replacement? and also I am curious what this part does in the operation of the bike.
Thanks in advance

[Spanner 1]

What your looking at is the clutch/neutral diode...... it's in the clutch safety wiring and allows for the start button to work while the bike is in any gear (other than N ) AND the clutch is pulled-in.
It wont read on regular 'Ohms' scale on a dig. meter but must be tested on the 'diode' setting on your meter, usually has a 'beep' to confirm continuity. Should beep one way, leads reversed, no beep.
These very rarely go bad IMO   

[Accolay]

It wont read on regular 'Ohms' scale on a dig. meter but must be tested on the 'diode' setting on your meter,

Is there something that is different about this diode that it can't be read by the resistance setting on a digital multimeter? Wouldn't the diode forward-biased read no resistance and reversed biased read "OL"?

[lucky]

It wont read on regular 'Ohms' scale on a dig. meter but must be tested on the 'diode' setting on your meter,

Is there something that is different about this diode that it can't be read by the resistance setting on a digital multimeter? Wouldn't the diode forward-biased read no resistance and reversed biased read "OL"?

A diode only permits voltage in one direction.

[TwoTired]

It wont read on regular 'Ohms' scale on a dig. meter but must be tested on the 'diode' setting on your meter,

Is there something that is different about this diode that it can't be read by the resistance setting on a digital multimeter? Wouldn't the diode forward-biased read no resistance and reversed biased read "OL"?

 Test devices often inject power into the circuit to be tested, and makes measurements upon the power that gets back to it.  This is how it determines, say, how much resistance is in the circuit being tested, and why you make these measurement with the power in the tested device off.  Active silicon devices are sensitive to voltage levels and activate into conduction when doing so.

If you are troubleshooting a complex device, activating the devices in it often makes it impossible to find faulty passive devices in the circuit if a device wired in parallel is activated during the test.  A 10K ohm resistor may read about 30 ohms if the diode or transistor junction wired along with it is activated.  To read the passive device properly would then require you to remove the active devices in the circuit you are testing in order to find the faulty passive components, or verify they are of correct value.  So, modern test devices usually inject very little voltage into the circuit and are very sensitive to what it gets back for measurement.  In this way, transistor or diode junctions are never activated into conduction, and don't have to be removed to find faults in faulty circuits.  However, you still need to find faults in active devices as well.  So, modern devices have a separate setting that supplies a slightly higher voltage which purposely activates transistor and diode junctions, allowing them to predictably conduct or not depending on the polarity of the power applied to them.

If you have a second multimeter, you can actually measure the voltage output difference between the various knob settings using that second meter.

Sometimes, it is better to know more than the built in smarts of the test equipment you use.   

Cheers,

[Accolay]

Thanks TT. Now that's the answer I'm looking for

[apehanger 550]

  Well, OK, and thanks for all the help.
  The starter still does not engage off the diode wire,so I am thinking possibly it could be the neutral switch. To test that,I guess I first will engage the clutch lever and go from there.If it spins the starter,the diode is OK I think, but i will try to test it as well. The neutral indicator light is not lighting up either, so that [neutral safety switch] may be the source of the problem.
  More fun and games with a bike that has been sitting for 21 years....
I will get back with results when they are known.
  Thanks,everyone.

[TwoTired]

Cb550 wiring changed during the 5 years of production, including the starter circuit.
Be sure you have the correct wire diagram for your bike model (whatever that is).