Blackburn 3.0 problem

[Buzz word]

I have just bought a Blackburn 3.0 cycle computer as i fancied a better way to keep track of how i was doing on my loops. I tried to fit the thing tonight and it has left me scratching my head. The cadence sensor works fine but the wheel sensor has me bemused.

The magnet is within the 1-3mm of the sensor. I have tried different positions of magnet along the sensor. I have tried waving a magnet in front of the sensor (verified to work from the cadence sensor). I have run the wheel round in top gear to check there was not a minimum cutoff speed. i have tried to pedal to see if the computer tries to link cadence and speed. I have programmed the unit with a preset circumference and a measured one to verify its calibrated. this was also repeated on both bike modes.

The only idea i have left is to use a continuity checker via the contacts on the cradle and see if there is a circuit. I don't want to do that as i don't know what the sensor is. my guess would be that its just a coil of wire and the computer measures a voltage pulse ala Faraday's law and if that works pulse voltage. However I am not sure is that is how they work and don't want to flash a sensor and destroy it if something more complex is in it.

I don't know if I'm missing something really obvious but i figure i have checked everything and cannot find fault, any ideas? that or its toast straight from the packet.

[Trooper2]

The sensor that you have is a Reed sensor (normally open magnetic switch) and can't be tested with a DVOM. In 15 years as a bike tech I had probably 5 out of 200+ bike computers that had bad sensors right out of the box, so it can happen.

I would recommend getting it exchanged where you purchased it.

[Buzz word]

Cheers trooper,
If its a reed switch that should be nice and easy to check. At least then i should be able to verify for my own peice of mind that it doesnt work.

[gbbird]

Are you sure the battery is OK, or batteries if it has several? When i recently fitted a wireless cateye computer i was getting no reading because the battery in the sensor was low/flat. I changed it and it has been fine since.

[Buzz word]

Its a wired effort so that should be ok. The main unit seems to light up and function fine except its dislike of displaying the speed. Contact issue could be a good call though i will have a look at the pins on the back and make sure they are joining up ok.

[Buzz word]

I just got in and gave it another look. I found that pin 2 and 4 were cadance so played with a magnet and the continuity tester to get bleeps. Tried the same technique on the wheel sensor and... It worked!? pins 1 and 3 made a circuit with a magnet on or waved nearby.

I checked by spinning the wheel, no computer and ... bleep, bleep, bleep like it should.

I figured the issue had to be with the unit so reset it and took the battery out a number of times. re checked the calibration information and... nothing!

cleaned the contacts, tried again... nothing

I guess the computer part must be dead as the sensors are picking up the magnet and functioning as they should. there are no more menu subsets and the manual doesn't mention anything it just doesn't seem to want to work.