Speed Sensor Question....

[jim7]

I have a 1998 sportster with a inop speedometer. I look in the maunal and there is a test to check if the paddle is working.... problem is the test in the manual is for a 3 wire sensor... (you add 12 volts to two wires and check for voltage movement on the 3rd) I have a TWO wire sensor how do you test that one????

Thanks for the help
Jim

 

[jim7]

anybody????

 

[stfoulks]

Same boat here Jim, same problem. Seems that as I've read articles on here since joining, people who ask about speedos are generally told to look over the side of the boat, and if you see water going by, that means you're moving - who cares how fast. However, I'm one of those guys who just can't stand to see something on my boat that doesn't work. I don't have an answer for you, but that sending unit is just too expensive if that's what the problem is. I've just switched to using my gps for speed (helpful when pulling the kids to know the best speed).

I hope someone gives us a break and has a trick for us!

 

[russssellcrow]

Same problem 1997 Challenger 787. 2 wire sensor (Blk/Yellow, Blk/Red wires).

I have a Fluke 23 multimeter (very accurate) and made some measurements on this sensor.
Resistance (Ohms) = 16.5 M (either polarity)
Vdc when spinning = 0.001 Volts (either polarity)
Vac when spinning = 0.001 Volts (polarity doesn't matter in AC measurement)
Conductivity (diode tester) = 1.508 V (Red + probe on Blk/Yellow wire)
Conductivity (diode tester) = OL (non-conductive) (Red + probe on Blk/Red wire)

I have no schematic, but it appears this sensor is a simple DC Generator Circuit (anyone have specs or know different?)
The little paddle wheel has North and South polarized magnets in each paddle (you can test with a simple magnet). As the wheel spins, the magnets pass in front of a wound wire coil (the 3 wire sensors probably use a Hall Effect Transistor). This is a simple AC generator (http://en.wikipedia.org/wiki/Alternator), the moving magnetic field creates AC voltage in the coil, which is sent to a rectifier (probably a silicon bridge from the 1.508 Vdc conductivity measured).

It appears the rectifier is still good in my sensor, but perhaps the coil or some other component is not. As usual, the electronics are POTTED (buried in black epoxy) so servicing involves digging the potting out with an Exacto knife. Oh Joy!

 

[jim7]

Let me know if you can fix it.. I am looking to 3 dealers and Seadoo to find a replacement.. Or if using the 3 wire is actually possible.. I'll let you know what they tell me

 

[russssellcrow]

Took the easy way out, got a Sensor off EBay for $35. This one was from a 90s XP, the wires were slightly different colors but still had the YELLOW and RED Stripes so I installed accordingly. Speedo WORKS!

Here is the weird thing, with my Fluke 23 meter, the static measurements were all the same. The only difference I could see was when I set to 300mV DC, and spun the paddle wheel. I got about 4-10mV response, which is almost imperceptible on a lesser meter. Now I'm rethinking the Black Box next to the paddle wheel. Previously I thought it was just a simple DC rectifier with a R/C circuit--WRONG! It appears to rectifying the pulses, and sending a pulse train up to the instruments. Confirming this would be easy on an oscilloscope, but most people don't have one.

 

[stfoulks]

3rd Wire off Speedo

According to a post I found elsewhere on the site, the 3rd wire coming off the speed sensor is actually a temperature wire.

I've check that my sensor is good, and have checked the wiring from the sensor to the speedo, all seems ok.

I have a question about the speedo plug... there are 5 wires coming into it -

Purp/Yell from speedo, bringing signal
Black/Red from speedo, ground
Dark Blue - instrument light
Black/Tan - main ground
Purp/Tan - ??? goes back to MPEM

My question is, with a voltmeter, should I read anything on the Purp/Tan wire at the back of the speedo when everything is on? Wondering if this could be my problem.

 

[jim7]

According to the manual.. On the 3 wire all 3 wires are used for the speedo... Not any for temp at least thats according to the test procedure on the 3 wire speed sensor .that's why I was having trouble even testing mine because the book does not have a 2 wire test procedure I have got intouch with Seadoo and they gave me a part number that will work I will post it when I get home...

 

[jim7]

Anyone find the 2 wire test procedure???