Monday, 31 January 2011

CPI GTR 50 Scooter Speedo fault.

A brand new scooter, there was no speed registering on the dash.

The Scooter is from Taiwan, not particularly common but a dig on the web bought some useful information.

Workshop manual here :

http://www.scooterunderground.ca/knowledge/manuals/documents/CPI_GTR50_SERVICE_MANUAL.pdf

Parts list here

http://cpiscooter.com/detaillants/GTR%20FRAME.pdf

And a nice snippet about speedo calibration lifted from a forum:

"Switch to TDO on the LCD and hold down on the right Handlebar button. Change the 4-digit number to 1840"

Adjusting this number adjusts the cal....

I was hoping to find that this had reset to zero but alas that was not the case, readign was set to 1840.

The electrical diagram showed the speed sensor was two wires into the main brain.

A quick look on the bike showed speed signal is derived from the front wheel, there is a magnet mounted on the front disk. This passes a sensor. Spinning the wheel gave no reading. Rapidly moving a magnet past the sensor briefly on one occasion gave a speedo reading ! This tended to indicate a faulty sensor.

The parts diagram showed you could unplug it before the brain. I had assumed this would be a magnetic reed switch so split the connector here and measure ohms of the reed.

The picture isnt the best but the speedo connector is sat on the top horn connector (sensor unplugged and removed completely at this point). I couldnt get a 0 ohm reading from the sensor with a magnet applied (it was permamnently open circuit).

I thought I would check the dash by rapidly shorting the cable leading to the brain (to simulate a good sensor being made and broken by the magnet). This gave no reading still and showed something didnt add up. I decided to measure at the brain to check the signal was getting there. Removed the speedo cowling, lifted the clocks (this is what Im calling the brain) went to check the cable leading to it and it just pulled away from the clocks !

I didnt take a pic but the connector to the clocks is the same as a motherboard ATX power connector.If you have ever fitted / removed one of those you will know it has a very strong latching mechanism and shouldnt just fall off !

So success, a loose connector the the brain all along, but interesting to trace it from the wrong end !

Now, rapidly shorting out the lead to the brain with a piece of wire registers a speed reading on the dash.

.. however, removing the sensor we managed to damage it. Should be simple enough to repair without getting a new original part (hard to see but the reed is embedded in some kind of resin and is cracked).



It is just a glass reed mounted inside a threaded body. I will mount a new reed inside and check.

The bike doesnt seem so well supported  (not sure if it still imported to the UK) but as per other comments I was finding on the web it looks good, is nicely made, components largely seem of good quality.

Update:

here is the new reed fitted. I sealed it back in the housing with silicon sealant.

10 comments:

  1. I am glad I have found you.This is my third attempt to post a comment. Maybe you've got the others. I have the exact same problem you had with speedo cable. I need help to fix it. The cable came out when I was working at the front of my GTR50. I peeled off silicone stuff and all I have now are two wires. Thank You

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  2. You should be able to replace the reed as shown in the picture. Or replace the whole sensor,  a threaded body reed sensor of the correct size should be obtainable from several sources (scooter repair shop, electronics catalogue) and not need to be CPI specific. Good luck.

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  3. Very informative. We'll definitely be linking to this on Twitter.

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  4. Hi and thank you for the information you have provided (invaluable)! I too have the same broken reed issue and have tried to source a replacement and have sourced several sources that carry a variety of reed switches (https://www.comus-intl.com/productpages/reed_switches_us.asp) however I haven't a clue with regard to which one would be compatible. Can you please tell me where you sourced your replacement and/or what the specific specs are? Really appreciate the help : )

    Cheers !
    Mike

    My email address is miksanpaur@gmail.com

    ReplyDelete
  5. Hi and thank you for the information you have provided (invaluable)! I too have the same broken reed issue and have sourced several places that carry a variety of reed switches;

    http://www.meder.com/sensor_mk11_plastic_us0.html?&tx_jppageteaser_pi1[backId]=2826

    https://www.comus-intl.com/productpages/reed_switches_us.asp

    however I haven't a clue with regard to which one would be compatible. Can you please tell me where you sourced your replacement and/or what the specific specs are? Really appreciate the help : )

    Cheers !
    Mike

    My email address is miksanpaur@gmail.com

    ReplyDelete
  6. Both the links are showing suitable parts, the first one with complete sensors, you just need to choose one with the correct thread size / length (sorry, dont know thread size).

    The link with the reeds, any would do that is physically small enough. As this reed is not swithing any current, just a signal to the computer you dont need to worry about voltage or current rating, and no need to be mercury wetted.

    Hope that helps.

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  7. Here's a good question. Any clue as to why a tach and speedometer won't light up, yet the other indicator lights at the base do. Ie. fuel light.
    This is a CPI GTR 50cc 2005.
    Is the solution to just change the whole unit. It's sealed and not serviceable.

    Regards,

    Neil

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  8. Maybe i'm a bit late to get an answer, but is this an inductive or a light sensor?

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    Replies
    1. Hi, it is a magnetic reed switch. There is a magnet mounted to the front brake disk that closes it. Hope that helps.

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  9. Greetings all! Just found this thread, it's been most helpful in establishing answers to a couple of queries that I've had, cheers!
    Can anyone tell me, if there is a specific manual or resource, dedicated to the speedo assembly, on it's own? Basically, I have one of these, new and unused and would like to use it, in a custom project. It would be great if I could work out how the speedo calibration can be changed to a different wheel size and if the rev-counter can be recalibrated for a twin-cylinder bike?
    Any ideas anyone? I can do a hardware fix for the rev counter, but if it's fixable, using the internal software, that'd be great!

    ReplyDelete