Giant Axact 9W computer fault

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RichardB

Slightly retro
Location
West Wales
In the middle of a ride, the computer (as per title) stopped working - speed display at zero, and the odometer stopped recording miles. Both head unit and wheel sensor have new batteries, the sensor is within range, and the sensor/magnet gap is >5mm, all as per the manual.

The head unit shows the correct time, and a speed display of -- when it's off the bike, which changes to 0.0 when I click it onto the handlebar mount, which is exactly what it always did. I'm assuming that this shows that the head unit's battery is OK, and that it is picking up the presence of the wheel sensor. But no speed or mileage when I actually spin the front wheel. I've checked everything against the manual (plus it was working fine until I stopped at the shops, and nothing was moved or altered), so I am now at a loss. I have removed a light off the handlebar in case that was causing interference. No change.

Anyone have any suggestions before I bin it and get another?
 

the_mikey

Legendary Member
You have four possible points of failure:
1: The wheel sensor
2: The magnet or wheel sensor triggering device
3: The computer
4: Radio interference between the wheel sensor and the computer

Cheaper wheel sensors work by using a magnet and a reed switch, and each pass of the magnet pulls the contacts of the switch together, triggering the sensor to register a revolution of the wheel, I would start here, verify that the switch is working, if you listen carefully you might hear it going click when the magnet is present, if you manually present the magnet (with the magnet in your hand, and using it to touch the sensor repeatedly to simulate wheel revolutions) this should enable you to test the sensor, also check your sensor and computer batteries are good.

Outside of this there's not much more I can suggest.
 
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RichardB

RichardB

Slightly retro
Location
West Wales
Thanks, that's helpful clear thinking. As above, both parts have new batteries, and head unit has display/sensor 'batt test' light illuminates, so I am pretty sure they are OK. I've spotted an error in my original post. The display goes from -- to 0.0 when the unit is mounted on the bike, but this happens even if I remove the sensor away, so the change in display is the unit registering that it is on the mount (there is a small metal pin which hits a contact on the mount).

Looks like the sensor is the problem - will check and come back. Thanks.
 
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RichardB

RichardB

Slightly retro
Location
West Wales
Hmmm. Sensor and magnet off the bike, I can hear a clicking when I pass the magnet over the sensor (didn't realise that was how they worked). If I pass the magnet over it repeatedly and hold it close to the head unit I get a speed reading. So it looks as though all is well, and perhaps the problem was that the setup had somehow been disturbed. Too dark in my garage to put it all back now, so will do that tomorrow. Cheers.
 
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RichardB

RichardB

Slightly retro
Location
West Wales
Sorted! I reassembled, checked and after a pause it started working again. I can only think that the wheel transmitter was at its distance limit from the head unit and the signal had become intermittent. Giant say <70cm and it was in fact 60cm, but I have repositioned to ~50cm and it seems to work. Good diagnostics have saved me a few bob as I was about to bin it and start again with a new one. Thanks Mikey!
 
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