XJ750Seca Speedo sender-How this device works??

Hello
This is a photo of the back of the XJ750seca speedometer.



I would like to ask if you know how it works.In wiring diagram this called senter.There are two wires.One black and one white/green.I know that the black is the negative.The green wire sends some kind of signal somewhere, but where??? According to the diagram(if I understood well) it leads to a device called cancelling unit.
Anybody got more info about how this device work??

 

I do believe that is your Reed Switch for the self cancelling turn indicators. It works by the magnetic relationship between it and the flywheel in the speedometer cluster. When the bike is moving, the flywheel spins and the reed switch is activated letting the self cancelling unit to be activated. From what I understand the cancelling unit is based both on time (10 seconds) and/or distance, about 120'...
I also understand that a replacement for the Reed Switch is about as rare as chickens teeth and very expensive if you find one. So be careful with it. Also Big Fitz has a great write up on servicing the Speedometer... here is the link to it.. http://xjbikes.com/Forums/viewtopic/t=15303.html

 

Replacement reed switches are as common as any old Yammie speedometer even if the speedo is broken. But they rarely fail.

Bruce is correct. The reedswitch reacts to the spinning magnetic drum in the speedometer, sending a "signal" (it's just switching on/off/on/off) to the automatic turn signal cancelling unit. It's how the cancelling unit knows the bike is moving; the signals won't auto-cancel if the bike is standing still.

 

Yep, it's what they said ^

Bruce, I think the rare & expensive bit is the self-cancelling unit itself.

 

Thank you all for your answers!!

 

It is. MSRP was over $100 and they are long unobtainable.

 

If you remove the reed switch from the speedometer housing, do so VERY CAREFULLY. They are quite fragile. Under the black plastic is a glass tube with a wire at each end. Pry in the center on the long sides. If you pry on the ends, you'll snap that glass tube. Been there, done that.

 

the reed switch is in here somewhere. i don't have one to look at or i could narrow it down a bit.
http://www.mouser.com/Electromechanical ... /_/N-5g2l/

 

wow, 8O have you ever opened one (old broken one obviously!) to see what's in there? I'm guessing, from that price & the fact nobody's remanufacturing them, that it contains some pretty complex electronics...

 

More like some bizarre first-gen electrical ingenuity like the TCI unit. It's not a normal "relay" there's definitely some circuitry there.

I've never laid hands on an "old, broken" one; as far as I know they rarely fail. Cancelling issues usually turn out to be wiring or switch problems (including the reed switch) rather than the "magic box" itself. Even though I have an NOS spare, I can't bring myself to cut into a good one just for the sake of scientific discovery. I'm happy with "ignorance is bliss" in this particular case.

Polock's right about the reed switch; reed switches are a commonly-available item (if you can figure out exactly what you need.) I just "harvest" them from scrap instruments.

 

Ah right, yes I'd agree on not dissecting a good one, especially a NOS one! 8)

Maybe if I find a cheap one on the bay I'll have a look just out of sheer bloody-minded curiosity might be that the one off the 900RK my frame came from has been listed by now, they seem to be listing all the parts after they sold the frame...

 

Yep, just picked one up for £8.60 we shall see... I'll try not to destroy it beyond gluing back together then I have an extra one too.