1983 XJ900 not charging

Hello,

A couple of weeks ago I purchased a 1983 XJ 900 which has been given the Cafe Racer treatment.
I was advised at the time that it wasnt charging and priced accordingly.

Here are my investigation readings obtained so far:

Stator: 0.47 ohms between all three pairs of white wires and no continuity to earth
Engine at 4000 output is 0.15v ac across all three pairs... a problem!

Rot0r: 4.7 ohms between copper rings + red and green wires at plug, brushes look new, good continuity and copper rings bright and shiny.

Regulator/rectifier: with ignition on, Brown to earth=12.3v
Green to Earth= 12.3v
with ignition off, +Red to whites and +black to whites have continuity and nothing when reversed.

I think that with the ignition on I should have 1.8v between brown and earth on the regulator however i cant see how this can be as the brown is connected to positive feed from the ignition switch as per the wiring diagram in my manual.

Any help, assistance or advice would be gratefully received..... cheers Mike
Back to biking after 25 years away!

 

I am not sure about the 900 FSM but the XJ750 manuals some have an error that labels V1 and V2 incorrectly. The brown wire is like you said and should be battery voltage, or close to it. The green wire is the control pin from the regulator, and yes it should be approximately 1.8V with key on and bike not running, and will then climb when the bike is started and RPM increased.

So that implies that either the rectifier regulator is not working or there is a broken connection at the main harness to regulator connector for the green wire

I have attached the correct version for the charging system

 

Thanks for the info... I thought there must be an error there..

Re the green wire... it passes from reg/rectifier through the rotor, via brushes to its brown wire and to a live feed... as I'm getting 12v from green to ground would this imply that the rotor may be at fault even though its impedance is correct at 4.7 ohms

Thanks in advance.. Mike

 

Hi Rooster..
So.. I've disconnected the rotor plug and getting 12v from the reg/rectifier.. this should be 1.8v and so indicate a new reg rectifier is required... have one on order..

The brown wire also reads +12v from ignition.. is this correct... 2x positive feeds going into the rotor?

Many thanks Mike

 

The regulators are quite reliable, but it looks like the issue here, and fortunately they are usually quite inexpensive.

Like I mentioned before the only other thing that would cause 12V on the green wire at the regulator connector is if the output of the rotor / brush (green wire) was open at the input of the regulator (green wire). And, in this case one side of the connector would be 12V, and the other side would be low so depending on where you probe that could make a difference

 

That would be correct, and it is the output of the ignition switch and sometimes presents the opposite problem of no charging, but excessive charging. If that voltage is reduced slightly because of poor contacts along the way the regulator will output a slightly high voltage, will which have a tendency to overcook the battery

Be sure to separate the main harness and the regulator rectifier connector and give it a good inspect for corroded / pushed / damaged pins. I am not sure what exactly would happen if the 12 volts reached the brushes, but did not reach the regulator. That may disable the regulator as that switched voltage is not only a reference but a power source

 

Many thanks for your advice..

No doubt more to come when the new reg rec arrives..currently going through all connections to confirm continuity

 

Hi Rooster..

A new reg rectifier received and no difference?!

one thing i have noted is that with the reg/rectifier disconnected, im getting +12v at the brown wire going to the rotor and the same +12v on the green..
would this point to a faulty rotor?

Thanks in advance,.
Mike

 

No, that 12V on the green wire only indicates that there is some continuity through the rotor / brushes. What it doesn't say is if there is good contact at the brushes, as you are opening the circuit so just about any contact will result in 12V on the green. In a properly operating system that contact between brown and green would be near 4 ohms, which when pulled low by the regulator would result in at least a couple of amps through the rotor to create a strong magnetic field in the rotor

And, you already reported good contact when you said "+red and green" wires at plug

So try reconnecting the Reg / Rect and with key on bike not running backprobe the connector on the regulator side and verify you have 12V on the Brown wire in respect to chassis. Then check the green wire again and see if it is still reading 12V. You reported 12V on both wires earlier, but the brown may not have been checked at the regulator connector

And. while you are there verify the black wire at the regulator is properly finding ground with a continuity check to chassis, and when powered up as above that pin has zero volts

 

Hi Rooster..

so,. with key on and not running and probing the rear of the reg/rec plug im getting :

brown-earth... 12v
green -earth...12v
Black-earth good continuity and zerov

for the earth im using the cclamp where the main earth cable is clamped to the rear of the engine?

do you think ive bought a bad reg/rectifier... it was from china via ebay..

Huge thanks again for your help and assistance..

 

not yet, but there have been some bad stories posted about some of the aftermarket regulators

One other voltage I should have mentioned is the red wire at the regulator. That connects to the battery through the main fuse so make sure at the regulator you measure 12V there

I saw this in another post where Franz commented his bike was not charging and stated:

"Are you getting 11 volts on both multimeters? My bike was not charging when l got it and it was because the brown and green wires to the brushes were connected to the wrong connector block in the wiring harness. I changed them over and that fixed it."

Now he has a 91 so it may be a different configuration and not possible on yours, but it might be wise to check continuity on the main harness 2 pin connector and make sure that green wire connects to the regulator green wire

I am still trying to bench test a regulator and having some issues, but worth noting that the green wire is pulled low regardless of the brown and red wires, the only other two wires that could be contributing to regulating the voltage

 

Hello.
Yes .. getting 12v on the red wire from rear reg/rec to earth

Have physically followed the green from its brush to the rear of reg/ rec connector and checked continuity along the way..
The brown goes from brush to 2 pin plug to positive feed in the loom, and from this junction another brown wire to the reg/rec... as per my manual..

Have also checked continuity across connector blocks..

Thanks again for your assistance.. currently trying to get a refund on my reg/rec and spend a little more from a UK supplier...

 

This is an interesting thread........

 

Interesting... hhmm... frustrating from my perspective..

So today I've gone back to my original reg/rectifier as 2 x replacements gave exactly the same results.. fitted a new stator and whilst the cover was off , re checked the rotor.. 4.7 ohms and no earthing from copper rings ..

No difference..

Any other theories re what I'm up against here would be gladly received... many thanks
.

 

I never say never with electronics, especially when dealing with a black box (regulator) where we don't know exactly how it is intended to work.

That said though, the above condition just shouldn't exist if the regulator is working, and the rotor and wiring appear OK as reported earlier in this thread.

Perhaps the +red should say brown?

The only explanation would be that the 12V reported on the green wire is not really 12V, but something different. Or, the regulator design is such that the control pin (green wire) is current limited and can open if excess current is detected, and despite the reported readings it is going into a current limit mode.


A step that could be taken to evaluate the rotor / wiring is disconnect the regulator from the main harness. Once disconnected set the DMM to measure 10 amps and with the ignition key on connect the green wire on the main harness to ground though the meter and verify at least a couple of amps, in theory very close to 3. If I were doing this just to be safe I would series a 5 amp fuse to protect the meter

 

Yes, I understand and feel for you. Unfortunately, your situation is providing you (and the entire rest of the world) with valuable insights and troubleshooting experience.

 

Thanks Chacal..

Mixed feelings about the bike currently..

Charging system is frustrating.. so have started cosmetic re furb.. this should improve the mind and maintain energy to get ontop of the charging issue..

Really appreciate all help and advice..

 

Hi Rooster..

So.. I'm getting 0.44 amps ,. Reg disconnected, Ignition on, from green through DMM to earth..

Still getting 4.8 ohms from brown to green, across the rotor. Could this point to dead rotor or bad wires?

Thanks again

Mike

 

So it sort of confuses things further or maybe indicates more than one issue since you are reporting 4.8 ohms from brown to green and that typically gets better with voltage vs the DMM ohm reading. However, in this case .44 amps is indicating 27 ohms through the wire/rotor/brushes.

So where did you ground the meter? Try the frame and engine and then try the battery negative terminal and confirm the reading is the same for all three

I suggested earlier to check the black wire on the regulator for zero volts and you confirmed. What did you use for ground - it should be the battery negative

And if all looks normal re-check the green wire again at the regulator connector and at the two pin connector with everything connected key on and confirm they both read 12V as before

Also check the green wire at the regulator with the DMM negative connected to the black wire at the regulator connector

 

Hi Rooster

So, after a couple of days away from the bike i have to admit a bit of pilot error measuring power through the Rotor..
This is 2.3 amps, green to ground(battery -, frame and engine) ignition on.

Black wire on regulator to battery - is 0 volts

Green to all three earths is 12.4v
Green to black is also 12.4v

There is a spare earth terminal from the battery - to an unused plug. I have no idea what this should/could plug into as there is
a good connection from battery - clamped to the rear of engine.??.

Have a great weekend and your thoughts on the above when you get a chance

Thanks Mike

 

So I am just about out of ideas, but thought I would ask are you running directly from the battery? No charger connected I hope?

I will post a simple check of the regulator in a day or two. It's a simple process and all you need is a high wattage resistor and some clip leads to connect it

 

Thanks Rooster

Yes,. Running off battery no charger involved..

Looking forward to the reg/rectifier test..

Many thanks Mike

 

So a very basic test on the regulator section of the Rect/Reg Assembly. The 6 ohm resistor is taking the place of the field coil.

And as far as what is going on with your readings with the field coil it really still boils down to a regulator, open wire. or incorrectly interpreted voltage to have the 12V at the green wire. The test with the resistor is a bit of a sanity check just to see if it duplicates the on bike reading. Could the regulators be getting damaged, yes say if the brown to green wire was shorted putting 12V directly on the green wire, but that would also mean Yamaha didn't include any overcurrent protection, which is a good possibility as that would mean designing for a shorted field coil, which is not likely. And, you have done testing that verified the field coil resistance and current, so that would rule out the shorted field coil situation

1. Using a 6 ohm 25 watt resistor connect one end to the green wire on the regulator, attach the DMM positive lead here also
2. Connect the negative lead (BLK) of the regulator to battery negative, connect DMM negative here
3. Connect the open end of the 6 ohm resistor to battery +12 and observe the DMM, it should read approximately 2.9 volts*
4. Connect the regulator sense wire (Brn) to battery +12V and observe DMM, it should read approximately 1.3 volts**

* approximately 1.5 amps if you happen to measure current
** approximately 1.8 amps if you happen to measure current

And caution, that resistor will get very hot

The 6 ohm 25 watt resistor is fairly common as they are used as load resistors for LED changeover
Preferably a DC power supply with current meter is used, but a standard battery is OK
Battery chargers not advisable as they may contain pulsed DC, which will affect the regulator operation

I managed to find this through Google and help from the website owner, and although not exact the figure 2 example is going to be very close to the design of the Yamaha regulator. I may go further one day but for now the "CONCRETE" encapsulation on the regulator has proved impervious to any attempt to remove it short of a sledge hammer

https://www.homemade-circuits.com/car-alternator-regulator-circuit/

 

Thanks Rooster..

Have ordered a resistor...

May take a short while to provide results...I very much appreciate your advice and help..

 

Missing Radio Shack now?

 

Don't remember ever having radio shack this side of the pond!

But yes .. its tricky to order single components.. Ebay is my friend..

 

Re connection of the dmm... red+ to reg/ rec green and black - to battery -

Thanks

 

Yes, the DMM will measure from green to black - I added the negative connection above that I left out

And I should have added be careful when connecting as the brown and green are adjacent to each other and shorting together could damage the regulator

Walmart, Autozone and others carry the resistors here as they are commonly used for LED conversions as load resistors, but they are a bit proud of them and charge too much

 

Hoping to hear if you found the problem. I’m having them same issue with a 82 xj750. New stator. New brushes. New voltage regulator. All resistance checks are good. All terminal connections look good. Getting ocv at green wire as well.

 

Found some bad connections. I’m good.

 

Still waiting for a resistor from China to test the reg/rectifier..

Pleased to hear yours was down to dirty connections.... can I ask which block..? I've measured continuity on all and ok... do you think i may have the same problem?

 

Hi Rooster..

So the resistor turned up eventually..

With battery + going through the resistor to green and black to battery -, I'm getting battery voltage (12.5v) from green to battery-..
This is unchanged when connecting brown to battery +.

I've measured the resistor at 6.2 ohms

I'm stuck

Thanks for your patience and any further thoughts..

 

It was actually the plug for the voltage regulator. It looked clean, but I cleaned it with electrical cleaner plugged it and took it apart a few times and the it worked. It seems as though appearances were deceiving.

 

You have three regulators? How many did you try?

Try posting a picture of your setup with measured voltage clearly visible on DMM

 

So, with DMM across the brushes your not getting around 12V when key on?

also, Did you do a rectifier diode test on the original reg/rectifier?

There is a way to use your metal shim gauges to feel for a magnetic field when on. it will pull a small shim to the axle bolt of the rotor when you turn the key switch on. That way you know there is a magnetic field.

 

Thanks for this.. will give it a go...

Getting 12v across brushes..

Bike only came with a replacement reg/rectifiers so can't check original..

Many thanks

 

Hi rooster..

I've uploaded 3x pics..
1 showing 6 ohm across resistor
2 showing 12.4v with feed to green and black earthed
3 showing same with additional live to brown control..

??

 

Question.. how do I hold a shim/ feeler gage close to the rotor axle with the cover on? As removing the cover also removes the brushes... would you attach 12v across the 2x copper rings manually?

 

This is an XS650 "slap test" I think it should work on an XJ so I'll test this on my XJ650 tonight.
If this works, it SHOULD tell you you have voltage and current to the rotor and thus magnetism. Then you move to the Stator/rectifier.
On my 78 XS650, my rotor was burnt, one of the 6 diodes in the rectifier was open circuit and the regulator (mechanical switching relay design) was switching at 16.5V causing an over charge situation.
So, when I replaced the rotor, I was not charging at idle and over charging at 3000rpm+
Had to replace rotor, rectifier and regulator.
There are differences I believe in the rotor grounding between the XJ and my 78 XS but I think they became the same in later XS models to match the XJ which has the regulator/rectifier all in one part. Thus if I got an after market XJ regulator, I would worry if its the right thing for the right bike with all the changes they did over time.

I did a butt load of reading and forum posting before fixing the XS650 and even bench tested the regulator with a variable power supply to see how it was set wrong. I'm an Electrical Engineer at a manufacturing facility so I had the simple equipment to do that in our technician's lab.

 

It does work on the XJ series, and I sometimes suggest it. However, in this case Michael has reported (most don't) 12 V on the green wire, which is the low side of the field coil (rotor). Consequently, that means no voltage drop across the rotor and therefore no magnetic field. The rotor has also been tested separately measuring the actual current through it, which was 2.3 amps.

If he would like, he could simply ground the green wire with the regulator disconnected and key on (as he did to measure current) and verify a magnetic field using the thin feeler gauge

So that's an important question to know if all three (?) test bad

I can't say much except that regulator is no good, once again is it all 3 that test this way?

And, as I tested 3 different regulators, including now the one off my bike that i have confirmed is operating normally. The power supply meter shows the voltage and the current in amps that would normally be rotor current creating the magnetic field

Red clip lead goes to 6 ohm resistor, green clip lead out of resistor goes to green wire on regulator, black clip lead goes to power supply return - DMM measures voltage across green / black and is reading 2.55 VDC

 

Thanks for this.. will purchase another reg/ rectifier... the other two were returned for a refund as although not bench tested the alternator didn't charge when installed... thanks again..

 

Rooster, in Post 37 he says he got 12V measured across the brushes.

 

He does, but I am guessing that is not a technically correct answer to your question as the 12V green to ground seems to overrule that

 

My Bad!,, sorry but I'm well behind the curve when it comes to motorcycle electronics... I do appreciate your help and hopefully get to the bottom of this problem... will get a new reg/rectifier on order + give the slap test a go.. thanks again..

 

I am not as familiar with the XJ alternator as I am with the XS alternator as I just got done replacing rotor, regulator and rectifier in the '78 XS. I understand that there was changes to the grounding of the brushes in that bike and the regulator in the 80's which I guess carried to the XJ.
The XS the green wire is SUPPOSED To be the + voltage and 12V on green to ground when on and not yet running. If that is incorrect for an XJ, I bet the seller of the reg/rect sold him the wrong part.
In my case, the reg was out of adjustment causing a higher charge voltage (it was an electronic coil with an adjustable tention screw), which fried the rotor and the rectifier.

 

Thanks..

Have ordered yet another reg/rectifier.. different brand but advised its a direct replacement and not from china!..

Will have a go the slap test at the weekend when free of work


Many thanks for your help so far..

 

I was thinking XS is six pin rectifier, and the XJ is a 9 pin rectifier / regulator

I would suggest testing it before powering it up on the bike just in case they are somehow being damaged. I don't see that as either the rotor would have to be shorted or the main harness would have to be shorted from brown to green or red to green. I think the testing has covered the rotor and brown to green, but maybe check red to green. I think the best way to do that would be disconnect the battery and measure red to green at the regulator with everything hooked up. Then set the ignition key to on with the battery still disconnected and expect to read the rotor resistance

 

Thanks.. should be in a position to test new reg/rectifier this sat.. will also measure rotor resistance as advised...

Many thanks

 

Hi Rooster.. so with the new reg/rectifier I'm getting 1.37v .. Green to black and with the control .. brown to positive im getting 0.07v..

Going to plug into bike now to test the rotor