79-83 Honda DOHC charging system procedures for troubleshooting, testing, and performance verification.

This looks like a huge page full of words, and might seem a bit daunting, but Iíve tried to break it down into small bites that shouldn't be too hard to swallow. It is my hope that users will find that before they have worked clear through the preparations and procedures to collect data for analysis, that their charging systems will actually start to work again due to main component failure not being the issue; rather, connection quality issues that are addressed along the way are what fixes the problem.

Let me know if I have made any glaring errors or can be of any further help. -genesound.

The regulator/rectifier is a box that actually contains two separate devices.

The regulator is what sends the power to the rotor. It adjusts the feed voltage to the rotor so the magnet gets stronger or weaker to maintain the 14.4 volts that it measures or senses on the black wire from the key switch.

The rectifier is made of 6 diodes that take the 3 phase power from the stator and rectify it into a single DC feed on the red/white wire that goes back to the battery via the starter solenoid terminal. The rectifier has no internal connection to the regulator, it's a separate device and could even be replaced separately as a stand alone piece by re-stuffing the appropriate pins (3 yellow wires and the red/white wire) in the multi-pin connectors

Prerequisites to taking charging performance measurements:

Testing results may not be accurate and/or reliable without first verifying the following items that are covered elsewhere on the http://www.cb750c.com site or in the reference materials at the bottom of this page.



Make certain that your meter is accurate. You don't need a super high dollar meter, but it does need to be reliably accurate.

A minimum 14 Amp/Hour battery that is known for certain to be good, has recently had a specific gravity test, a load test, and been fully charged overnight. There isn't a charging system in the world that will charge a battery that is no longer viable, so test the battery before you waste any more time on fiddling with the charging system. We have had numerous people this year that started messing with the charging system for days only to find out that their battery was junk, so check it, even if it is "supposed to be good".

The Rotor should be verified to have between 3.6 Ω (ohms) and 5.4 Ω of resistance between the slip rings. This isn't always the end of the road for rotor testing though, if it seems to be good and measure OK at this point. It can still be failing when it's hot and spinning and running because centrifugal force causes the windings to short together. We will be able to test for this later, once we are ready to take some running voltage measurements.

The Stator should have between 0.4 Ω and 0.5 Ω between any pair of yellow wires and no continuity between any yellow wire and ground. This is the least likely charging component to fail, but it does happen. The continuity and short tests are usually definitive for these though. Some rewound stators have been found to be higher in resistance, closer to 1 ohm between any pair of yellows, and still work fine.

The Brushes should have carbon left beyond the end of life marks, have good springs, and the brush leads from the connectors to the brushes tested with the ohmmeter, and have less than 0.5 Ω resistance, almost 0 Ω from the connector to the brush face. Wiggle and tug slightly on these brush wires during this test to make sure they aren't flaky or intermittent.


Connection Quality Is Extremely Critical To Charging Performance!!!:

Many charging problems on old motorcycles can be traced to dirty, corroded, or burnt connections or the key switch.

A loose, weak, or dirty connection or key switch can cause improper or erratic charging system output. A melted plug is also a sign of a loose or dirty connector. The heat comes from the resistance of completing the circuit through oxide (or oil and dirt) on the surface of the terminals.

Check all the connectors. The battery cables and all the other wiring connections should all be clean and tight. With pin and sleeve type connections, where a blade inserts into socket, like in the multi pin connectors, the pin, or blade, needs to fit into the socket very snugly to make a good connection

Don't mistake the drag of the plastic shells when judging whether or not the connectors are tight enough. They should kind of be a PITA and hard to put together and separate from the friction of the actual connector pins in the sockets. When you put them together then take them apart, you should be able to see a clean shiny scrape mark on the metal pins left by the tight female connector if you look there with magnification. We need bare hard metal to metal contact, right through any dielectric grease or corrosion. The grease is there to help stop corrosion, it's not there to be a conductor, and should not be.

It's like trying to get a good 4 ohm measurement reading on the rotor, you have to push like hell on the rings on a shiny place with the probes of your meter to get the meter to settle down to the lowest reading it can. That's the difference a tight connection makes, and what is necessary for really good charging system performance where you need to pass significant power. You need every connection to have less than 0.1 Ω of resistance ideally, because they add up and make the voltage drop that you measure in steps 7 and 8, and that is critical to good charging performance. There cannot be more than about 0.1 Volts of voltage drop on tests 7 and 8 or your charge isn't going to get to the battery very well.

The Oregon Motorcycle Parts link at the bottom of this post has some very good connector cleaning info with how to take them apart and change pins and such linked in it.

Make sure that your connections are all clean and tight and not dropping voltage before you try to troubleshoot the main charging components with voltage and current meter readings.

If the connections are bad, troubleshooting to find faulty major components will not produce accurate and reliable results, so preferably clean and tighten them prior to taking meter testing results to send in to the forum for analysis. You might even get lucky and have everything start working right just from that cleaning and tightening of connections.

Do not let your motor sit running too long getting hot without adequate fan cooling.

Testing Instructions:

Below are the charging system tests, with steps numbered 1-9 and some a,b,c,d part answers as well.
Perform these tests with the meter probes poking the connectors or through the insulation, with all the connectors
connected, running at 3000RPM unless it says otherwise for a particular step.

Make your own new Technical Help thread with the information you record in it, see **Results Section below
Someone should answer your post and be better able to help you armed with this data.

These are the instructions for each test. Put your answers in a list like the one below the instructions in the Results Section.
The values in parenthesis are the "perfect world" values, probably almost never exactly that.

1a. Check System Voltage - measure DC voltage at battery terminals w/ motor off key on (~12.5VDC)

1b. Check System Voltage - measure DC voltage at battery terminals @ idle (~12.5VDC)

1c. Check System Voltage - measure DC voltage at battery terminals @ 3000RPM (~14.4VDC)

1d. Check System Voltage - measure DC voltage at battery terminals @ 5000RPM (>14.4VDC)

1e. Check System Voltage - measure DC voltage at battery terminals @ 3000RPM with Regulator Bypassed *see 3d for bypassing the regulator explanation and do this measurement at that time.

2. Check for rotor magnetism by dangling a .0015" feeler gauge by the alternator...(yes?)

3a. Rotor voltage - measure DC volts between black & white wire on Alt/Stator connector (measure w/ motor off key on)

Rotor voltage - measure DC volts between black & white wire on Alt/Stator connector varying DC voltage measure @ idle .

This voltage increases and decreases duty cycle as the motor runs to regulate the output of the charging system by making more or less
magnetism from the rotor as needed to keep the battery at 14.4 volts when everything is working right. The meter reading wonít give a

complete picture, since itís a duty cycle, but it helps.
(Could be as much as battery voltage at idle, and less at 3000 RPM)

3c. Rotor voltage - measure DC volts between black and white wire on Alt/Stator connector varying DC voltage* measure @ 3000RPM.

3d. Rotor voltage with Regulator Bypassed - measure DC volts between black and white wire on Alt/Stator connector. @ idle

How to Bypass the Regulator - However, before bypassing the regulator, make sure the field coil (rotor) isn't shorted. (You already did that, right? )
Leave the alternator connector coupled, and insert an unwound large paper clip into the connector at the WHITE wire location. Run a jumper wire from the paper clip to the battery's NEGATIVE terminal. Now repeat the charge amps test, but this time, DO NOT EXCEED 3000 RPM, the voltage could go dangerously high. Also do not let it run long like this. - If the alternator starts charging, the regulator is likely the problem. This effectively bypasses the regulator and makes the charging system produce full unregulated output. If everything but the regulator is working the voltage could go quite high, so donít rev too high, and donít do it for long.

3e. Rotor voltage with Regulator Bypassed - measure DC volts between black and white wire on Alt/Stator connector. @ 3000RPM

Stator voltage - measure AC volts between any yellow to any yellow wires on Alt/Stator connector (~8 to 15 VAC)

Check rectifier - out measure DC volts - red/wht wire to green wire on small r/r connector (≥14.4VDC same as battery)

6. Check regulator - reference/rotor supply - measure DC volts at black wire to green wire on small r/r connector (14.4VDC)

7. Check r/r ground conductance quality - measure DC volts (voltage drop) - green wire on small r/r connector to battery negative terminal (~0 VDC)

8. Check rectifier out feed conductance quality - measure DC volts (voltage drop) - red/wht wire on small r/r connector to battery positive terminal. (~0 VDC)

9. Also check DC amps into battery at fuse connector as per Mike Nixon's guide:

Charge Amps Test
Set up your multimeter for its highest current scale, usually 10 amps.

Key off: Remove the bike's main fuse, and clip your meterís leads in place of the fuse.
Check polarity by turning the keyswitch on:
If an analog meterís needle swings backward, that's good. If forward, reverse the connections.
On a digital meter, you want a "Ė" (negative) sign.
Start and rev the engine to 3,000 rpm. Should read positive amps on meter; the result should be at least one-fourth
of the battery's amp/hour rating which is usually at least 14 Amp/hours (so, read over 3.5 amps).

**Results Section:

Copy and paste the list below into your own new Technical Help thread and fill in your readings using the instructions above

Include a description and any other information you have regarding your charging system problem

1a. System VDC - @ motor off, key on _______________

1b. System VDC - @ idle __________________________

System VDC - @ 3000RPM ______________________

System VDC - @ 5000RPM ______________________

System VDC Bypassed @ 3000 RPM _______________

2. Magnetism? ____________________________________

Rotor VDC @ motor off, key on __________________

Rotor VDC @ idle _____________________________

Rotor VDC @3000 RPM _________________________

Rotor VDC @ idle regulator bypassed______________

Rotor VDC @ 3000RPM regulator bypassed ________

4. Stator VAC ____________________________________

Rectifier out VDC ______________________________

Regulator Black wire VDC _______________________

Regulator Ground wire VDC _____________________

8. Rectifier wire Voltage drop VDC _________________

9. Charging Amps DC ____________________________

Additional Information: __________________________

References and Notes:

Thanks to the following sources of information used in compiling this testing procedure.
Familiarity with them is advisable before attempting to troubleshoot the charging system.

Meter reading help:

Honda CB1000C Honda Shop Manual:

See Chapter 18 Battery/Charging System of the CB1000C Honda Shop Manual. Click here or right click to go there or download according to your browser.
It has a little more info than the 750 Shop Manual, and it's for the same parts.
Rotor continuity test: 3.6 to 4.4 ohms was accurate for new rotors from Honda, however rewound rotors will often
work fine at resistance up to 5.5 ohms and possibly even higher.

Mike Nixon's electrical troubleshooter article:
Link to Mike Nixon's Charging Troubleshooting doc

2 Ω 120 Watt power resistor for Mike Nixon's Stator Test

Oregon Motorcycle Parts troubleshooting faq: