Throughout production Yamaha basically installed the same charging technology. Rotor spun inside a battery induced magnetic field creating an AC current converted to DC by a slicone rectifier (6 diodes).

Pre 80 models had a mechanical regulator controlling voltage before the rotor.

80 on used a solid-state rectifier/regulator combi which controls voltage after the rotor.

These systems have provided reliable service for a long time now. Most problems stem from bad battery, worn rotor brushes, dirty or broken wire connections, dirty or worn ignition cylinder. If you have charging problems best fix it. Better sooner than later.

A bad battery kills a good charging system. A bad charging system kills a good battery.

Although easy to troubleshoot and repair good parts are becoming harder to find. Rewound rotors expensive and not necessarily reliable.

Earlier adaptations of later model RD350 alternators provided relief – but were still old. Advantages were instant current production and the ability to run battery-free. Today, off-the-shelf bolt-in kits are available.

In the garage are 2 bikes with PMA conversions (1 an RD350 conversion, the other from Ants – both points), 1 with total loss, and 2 with original systems (1points, 1 Boyer). One of the original chargers, 79, with mechanical regulator has decided to rebel. Battery flat after a couple of hours riding, headlight on.

I have a spare RD350 conversion boxed, in the corner. Do I put it in?

If your battery is suspect, the ignition-block, fusebox or wiring damaged or dirty – nothing you do will solve your problem. When you are absolutely positive these are ok, check them again. This is actually most of your work done.

 

What do you know about your bike? Curly rulz!!

 

 

Battery voltage: Static? (around 12.5VDC) … Active? (max. 14.5VDC @ 2000 rpm)

A quick Slap-test gives an indication how good your Regulator and Rotor are. I hang a 17mm ring spanner off a screwdriver, poition it close to the alternator cover and turn the key on. It should pull into the cover and release when the key is turned off.  The more positive it reacts the better. Mine was good.

Check voltage at your brushes. Green wire. Key on. Motor not running. It should be max. 0.3VDC less than your battery reading. Weak  voltages create weak magnetic fields. Check your wires. Battery, earth, fusebox, ignition block. No real point in going any further until you solve this. First time I had 5.4VDC. Cleaning the 6 wire connector gave me 11.5VDC. Battery earth strap both ends sanded and washed, 11.9VDC. Battery +ve, heavy end to starter solenoid. red to fusebox and ignition-block. Washing the ignition-block out with brake cleaner and cleaning the brush connection gave me the rest.

You may, now, only need new brushes. Check them. Min 7mm. The outside brush will be shorter than the inner. Its’ path each rotation is longer.

I usually remove the stator.

Gives direct access to the rotor. Meter on Ω, Ohms. Ring/Ring should be 5.0 – 5.5 Ω. Ring/Earth, infinity. Inspect for damage, discolouration. The dirtier and darker the windings the more likely the rotor is defect.

Check the stator. Damaged wiring? Discolouration? Smell? Mine was quite oily. Where did it come from? Crankseal? Cable-pass hole? Gave a quick sqiurt with brake cleaner. Unplug the 6-wire connector. White/White should be around 0.5Ω. All 3 combinations. If not disconnct the single yellow wire and repeat (tests the safety relay). White/Earth – infinite. Plug together. Motor running. Meter to VAC. White/White 10.5-11.0 VAC. Low readings indicate a grounded Stator. High readings, a bad Rectifier.

TBC: pics, rectifier and regulator tests

So, if you’re having problems with your original charging system don’t simply throw it away and get a PMA. Check it. When you find a problem keep checking – there may well be more than one issue.

For me here, once I sorted the voltage at the brushes I was fine. A quick readjustment of the regulator and all was good – didn’t even need to replace he brushes.

If you do decide to replace it, be aware that if you have electronic ignition you will need to replace that too.

Ants produces a direct swap kit for points models that i am personally very happy with. Powerdynamo also have a combi PMA/Ignition.

Sourced and installed the parts from an RD350LC PMA into my blue rat some years ago . Used. Old. And still good. Very happy with it.

A year or so ago I picked up a nice low mileage 77 D. Ridden a few miles every year. Complete paper record. Had some charging issues.

About this time Ants from the British XS650 forum began providing new PMA units for a good price. 200W. Complete with rec/reg, a rotor cone key that fit the original XS650 crankshaft and timing marks. (if trying the link dont be put off if you get a blank page – simply reset and it will appear – dont know why it does this but it happens to me all the time)

 

 

Was pretty busy for a while and it sat. Eventually got a chance to blow the dust off and begin.

 

Checking that the stator screws were loctited in – Yes.

 

Sometimes this locating pin just wont come out. Easier to quickly modify the backing plate

 

The pin sits at 6 o’clock so a simple line perpendicular to the horizontal gives the position

 

Backing plate didn’t sit properly over the crankshaft seal boss so got busy with a file. Would have been quicker to head off to the workshop and chuck it in the lathe. Naya.

 

Took a little while.

 

Sits perfect now.

 

Cut-out and reshaping will be now be done during production.

 

Phase wires held in place with a clip. Used another on the plate screw to the right just to keep clear from the chain and secured cable with a frame tie just below the rear engine mount.

 

Also removed the blue neutral indicator wire from the old loom, resheathed it in 4mm isolating sheath and reconnected to the original position. (Plug connector upper left in next pic)

 

This is the original regulator. Remove it.

 

 The rectifier too. Sits under the battery box.

 

Remove the battery to release the rectifier.

 

Made a plate to mount the new 5 wire rec/reg in the original reg position so the fins didn’t block the airbox inlet. Would have welded tabs directly to the battery box but had run out of wire for the MIG. The 3 screws with nuts create an air space under the rec/reg for cooling and better air flow to the filter-box. Packed with rubber bushes they dont rub against the underside of the rec/reg.

 

Fits snug between the tool box and filter-box. Cables separated, resheathed and fitted with original connectors

 

Release the original connector blocks by inserting a small flat bladed screwdriver into the recess beside the pins. Simply push out.

 

Make sure the tangs are reset before reusing.

 

Added a 20 Amp flat bladed fuse holder in the positive battery feed. Just for security. This wire is too long and will be reworked.

 

The rec/reg, when mounted on the plate, interferes with the sidecover. Modified an old sidecover. Rattlecan-blacked it and it’s mate. Be a shame to mess up a good set of covers

Just got to put some kms on her now to road test before installing a 750 kit that’s been sitting on the shelf for a couple of years.

Had some charging issues in the beginning. Went through and checked the new wiring. Not quite sure what was wrong but the issues disappeared.

More than happy with this.

Update … almost killed my second rear tyre now – no problems – running sweet

Ant’s: This is a good product – once I installed it, 2.5 years ago, I have had no problems .. !!KOOL!!