Hi all. New member here - I am trying to help my buddy get his newly acquired AT2 running correctly.

With a fully charged battery (from a tender), the bike started off the e-start and ran great. After an hour or so of running, it started misfiring so I put a voltmeter on the battery and found it at 2V.

After some googling, I found myself here and reading through a bunch of threads of other people working through generator problems. I then downloaded the service manual here and started working through the troubleshooting procedures. Here is what I found:

- Resistance across terminals F & A = 5ohms
- Generator output test = 0V

The generator test as described didn't make sense to me, because I was measuring continuity to ground from the A terminal with almost no resistance. So with the grounding of terminal F it seemed like it would never have output. But going back to the service manual, it seems like there should NOT be continuity to ground from terminal A? So I then did the following:

- Unscrew the positive brush pigtails. Test if the brush has continuity to ground while pressing against the commutator. YES.
- Remove the positive brush, and check whether it's mounting plate has continuity to ground. NO

Incidentally all 4 brushes look in great condition and are no where near the wear lines. This bike has approximately 2,000 miles on the odometer.

So my question; should the positive brushes have continuity to ground when actually pressing against the commutator? I assume the answer is no, but want to confirm that I am understanding the system correctly. ie. Are the 'pads' on the commutator that the brushes push against somehow insulated from one another and from the core?

If the answer is no, there should be no continuity, the next question is what typically causes that to happen?

I note that when I shine a flashlight at the commutator where the removed brush would locate, the grooves between the 'pads' look full of something. Gunk/dirt I guess. Would that be the likely cause of the problem?

Thanks for the advice. While I'm pretty handy with a wrench and have been riding some time, I've never dealt with this kind of system before.

Cheers,
-James

 

 from near Salisbury, UK, James.

I believe that the RD200 uses the same type of electric start and charging mechanisms as the AT bikes. With that in mind, please see below two answers to related questions regarding the RD200 from another forum.

Please don't expect me to answer any questions on these statements as a) they have been nicked and are not my own work and b) your existing knowledge sounds far greater than mine! 

 "This is a fairly crude explanation (crude as in my knowledge on this isn't complete). The RD200 dynamo/starter has no permanent magnets, but two sets of coils, one fixed one rotating. Before the motor is started a small voltage is applied to the field coils (via the red charge light). As a result the field coils become an electro magnet. When the engine starts to rotate, the other set of (multiple) coils pass through this magnetic field which produces an electrical output. This is fed via the brushes and regulator to both the battery and to the field coils. As the voltage rises, the magnetic field gets stonger and the output increases, the field gets even stronger and the output further increases etc etc. This will happen very rapidly until the wires melt or the engine stalls. Fortunately the standard mechanical regulator stops this, by opening and closing a set of points that control the voltage to the field coils. If the voltage rises too high, the points open. As the volts drop again they close. There are actually several lots of point's in the RD200 regulator controlling voltage, current, starter and a set to stop the battery discharging. There's a lot to go wrong and it's all mechanical." 

"Within the voltage regulator there is a relay that swaps the dynostart from generator to starter. Pressing the starter button you should hear a distinct click from the regulator.
Common problem is the earth to the handlebars from all the powdercoat. Jump a cable from battery negative to handlebars. Similarly repeat directly to the start contact on regulator to eliminate. Do check the wiring diagram for right connection otherwise you will cause damage"

Back in the day the only problems that arose was when brushes got worn down to the point of spring hanging up & not pushing. If the electric start worked then i guess at least two brushes are ok & generally they all wear similarly. Have had the battery fitted wrong way around which you can get away with on a dc system, just doesn't charge. Well--ok not sure if the starter would work either, but doesn't go septic like an AC system. I'm no help in diagnosing but the comutator must be connected between segments & the [whats it called] mica should be below the surface, & nothing to earth, armature core. & guessing the field coils must 'not' earth either if you tested it with the ends disconnected. Pretty reliable system--50 years ago. Close the cutout by hand very briefly & see if it makes the armature kick a little to show contact all the way down. & check bat for reverse fitting. Not that i think you'd do that for a minute.

If you go through the test and troubleshooting procedure from start to finish most of your questions might be answered? 

Another good resource is the 1969 Yamaha Shop Guide as well as the earlier AT1 manual

Two brushes are for starter, other two are for generator. 

Does starter work?  (I'm guessing no)

Carbon in the mica gaps is conductive and will short the bars to each other...  which might be causing your issue?

Mark mate, says started of the electric start & ran great untill it went flat. Sorry--i'm going outside to fit a tyre now & not gonna look again. Have a happy day.

Thank Morley...  also said it ran an hour which confused me.  Every gen model I ever saw that wasn't charging died in 15 minutes or less starting with a full battery?  Thinking it might have been failing...  wonder if starter works now with battery charged?

Anyway, that's all I have anyway...  probably something else completely...  I guess I never tried to "figure out" the tests...  I just followed them exactly and always found the problem.  Lucky I guess. 

I'd be next to useless sorting these generators when things have been played with by 'experts' in its 50 years & think i must be dyslexic when reading test procedures--better if someone reads it out loud. Luckily they were very reliable when i was working on them in 'the day'. Just brushes & that was about it.

Thanks all for the thoughts/guidance.

My issue is that I was getting a fail result at the first test - 'Field Coil Brush Insulation Test' - and as noted I didn't see how it could ever pass. However I just re-read the service manual and realized the photograph shows the yoke OFF the bike. ie. without the brushes in contact with the commutator. Duh!

Makes a hell of a lot more sense now with the yoke removed from the bike!

So, I am proceeding through the rest of the tests and will report back - hopefully with progress.

GR8UNCLEAL: Thanks for the welcome. Salisbury is beautiful countryside. I'm from Shrewsbury, Shropshire, but have been living in Colorado for 20+ years.

-James

The 1969 general shop manual is much more clear about things like isolating brushes from the commutator...  and has a lot more "Theory". 

 

Update:

Since the commutator was black, I sanded to clean copper with 800 grit then cleaned the grooves with a toothbrush and contact cleaner. Cleaned the brushes. Sanded every single electrical contact.

Fired up the bike - got 5 seconds of sparks coming off the commutator then it bedded in and I'm immediately reading charging output. From 13.x volts just above idle to about 15.5 volts at upper RPMs before the regulator cuts.

Deep clean was all it needed. So happy right now!