Bicycle Mechanics - Computer issues - what fun...

After getting by bike back from having a service, I slotted the computer back into its cradle and now it won't pick up a signal from the sensor. I tried moving the magnet to a different spoke, realigning the magnet and sensor, wiggling wires, cleaning the computer and cradle metal contacts, taking out and reinserting the battery (at the expense of my odometer reading) and all sorts of other things... still no signal.

Any other ideas?

Cheers,

Binnsy

There must be something wrong with the reciever probably. If the screen is working, then the commputer must be working, so it might be the reciever that picks up the magnets signals.

Is your magnet close enough to the sensor? They should almost touch. What brand is it? Some types of cradle contacts can loose spring force and thus loose contact. They would need to be sprung back out. Others are pretty much solid.

Any ideas on what to do? Give it a whack with a spanner? Believe me, I'm tempted...

mtbikerinpa, the magnet is about 1mm away from the sensor (I moved it closer in my attempted repairs, even though it worked fine where it was before)... The contacts looked fine... Dunno, maybe they need a bit of buffing or something...

As for the brand, it's a generic AU$35 one I picked up from the bike section of a dept store. But it's worked fine before now...

I have had a few cradles go bad too. A new one is usually about 10 bucks, so I tend to buy a couple. When I was freeriding a lot id wear out the wires about every 5 months. The wire may have gotten yanked too. If you have access to a meter, see if there is any conductivity through the sensor by using the ohmeter function. There will be resistance, but if it has some conductivity it should be alright. Then it lies in the contacts or computer itself. I have had all of the above fail at different times.

Fair enough... I've had the computer for about two years... so I guess I can't complain if I have to fork out another $35 for a new one. I have a multimeter so I'll check the conductivity.

When the magnet swings by the sensor do you hear the relay click? If it seems like the magnet is tripping the sensor I'd be inclined to attach a multimeter to the computer shoe to see if the wires between the pickup and the shoe were in good shape.

edit: umm.. yeah, which is what other people have said. I guess it pays to reload before replying.

I have a multimeter so I'll check the conductivity.

Connect your ohmmeter to the two contacts on the cradle. I do this by holding the probes like chopsticks and leaning on the contacts. Now, while you have the probes on the contacts move the magnet back and forth past the sensor. You should see the circuit openning and closing. If not, the problem is in the sensor cable or sensor switch itself. I would suggest cleaning the contacts in the cradle and on the computer with an eraser and with a q-tip moistened with alcohol. I have a digital camera that pretty regularly will go on "low battery" even if the batteries are all charged up and checked with a meter, and the only thing that will fix the problem is to use alcohol on the battery ends. They look clean as a whistle, but I still have to clean them to make it work. Low voltage contacts can be really fussy about the slightest bit of contamination. You have four contacts between the cradle and the computer itself - if any one of them is contaminated it can kill you. I say use an eraser and alcohol because sometimes one will work and sometimes it's the other. Also, I have had an intermittant open cable right where it went into the switch sensor housing. It drove me nuts trying to find it, but, in the end, it would open and close the circuit just by wiggling the cable. Hope this helps ;-)

Binnsy: Is there any way that the wires particularly near the fork could have been stretched particularly by giving the handle bars an extreme turn? I had that experience recently where the line was effectively shortened by slipping down around the nut on the brake calble and was broken internally by an abnormal turn. I wrap the excess wire around the bake cable on its way to the handlebar.

If you still have no luck, get a wireless computer and count yourself lucky. I've never had a wired computer last 2 years.

Maybe a new battery?

He already tried a new battery.

On the use of the meter:
The reistance of the coil/aka sensor is constant, whether in motion or still. When you move the magnet you are inducing a voltage through the coil in the form of a pulse.The computer senses the time span between these pulses to determine speed. The fact that the pulses are of such a minor voltage is why the meter is yet unharmed by moving the magnet. If an ohmeter is connected and the voltage was sufficient it would either blow a fuse or damage the meter internally, since ohmeters have thier own power source. The function to use if you are looking for pulses is either the Ammeter(amps) or Voltmeter, since they are passive reading.

He already tried a new battery.

On the use of the meter:
The reistance of the coil/aka sensor is constant, whether in motion or still. When you move the magnet you are inducing a voltage through the coil in the form of a pulse.The computer senses the time span between these pulses to determine speed. The fact that the pulses are of such a minor voltage is why the meter is yet unharmed by moving the magnet. If an ohmeter is connected and the voltage was sufficient it would either blow a fuse or damage the meter internally, since ohmeters have thier own power source. The function to use if you are looking for pulses is either the Ammeter(amps) or Voltmeter, since they are passive reading.

Excellent description of how an ohmmeter works. I have actually dissected a couple of failed wired-type sensors and they used magnetic reed switches, not coils. In a switch based sensor the circuit resistance is NOT constant. You need an ohmmeter to test this type of sensor. I am not saying there are not coil based sensors out there, but not all sensors are coil based.

Any ideas on what to do? Give it a whack with a spanner? Believe me, I'm tempted...



Sorry I missed this before. The last thing you want to do is whack it with a spanner. If it's got a reed switch in there, these are pretty fragile. If it's coil based, then it's very possibly got a ferrite core which would also be very fragile. It's looking for a magnetic field, not solid steel ;)

Out of curiousity, what brands were those with switches? I have never run into one, but it is an interesting design concept. My experience has been with Specialized mainly.

My Cateye uses a reed switch. If you spin the magnet past the sensor and hear a small "click" it's a relay-type sensor.

Another newfact for the day :)

Out of curiousity, what brands were those with switches? I have never run into one, but it is an interesting design concept. My experience has been with Specialized mainly.

Two of them(that I can remember) were Treks. Magnetic reed switches have been used as proximity sensors for decades. Burgular alarm sensors using a magnet on one side and a reed switch on the other are very common. That they can make an audible click is something that I forgot about, but that's probably because I don't hear as good as I used to :rolleyes:

I just bought a new Sigma Sport computer, and it hasn't worked since I put it on the bike. I put it close enough to the sensor to pick it up, but hasn't worked. Any suggestions?

I just bought a new Sigma Sport computer, and it hasn't worked since I put it on the bike. I put it close enough to the sensor to pick it up, but hasn't worked. Any suggestions?

Is it a wired, or wireless type? If it's wireless, there is not a lot you can do:

1. Get the sensor and magnet close. Try moving them up and down in relation to each other.
2. Assuming the batteries are new in the computer and the sensor housing:
a. You can see if the computer battery is good or not from the display.
b. The sensor battery is a different story. If you touched the battery ends or there is some
contamination in the battery compartment, the sensor may not "send". Try cleaning the
ends of the battery and the battery compartment contacts with alcohol. Just moisten the
end of a q-tip. Check to make sure the battery is installed in the correct polarity. Yes,
I know that seems obvious, but people do it all the time. Meter the battery if you can.
Sometimes the batteries that computers get shipped with are dead or low by the time they
get to the consumer.

If it's wired, please refer to the earlier posts on this thread. Remember that the contacts in a cradle and on the computer can be very fussy about the slightest bit of contamination - and, you aren't necessarily going to see it.

As you can see, without a meter there are some important tests that you just can't do. I'm sure there are plenty of folks on the forum that can help with meter usage, if you need it.

Best luck :)

On a theoretical note:
Could that be one difference between systems that run long time and those that don't?
My Specialized comps run longer if used a lot and typically go for almost 3 yrs on a battery. They would not be using a reed system, rather they would use the pulse generating coil. That would reduce the current draw for the system since the coil would be making its own power. Thus the comp head runs less power draw overall.
In a reed system the computer head is supplying 100 percent of the power and the switch would merely be closing the circuit to make the pulses. Advantage maybe being greater pulse energy, and thus reliability at cost of battery life.
Maybe its all different, but I was just curious.

He already tried a new battery.



And just where does it say that?

Actually, if anything it would probably the opposite. Having built capacitance/voltage sensing circuits, the sensing was an active process. On the other hand, with a open/closed relay, you can rely on an interrupt driven system, leaving the processor asleep until such time as it's interrupted by a open/closed transition.

But that's just a guess.

I see what you mean, Im just trying to reconcile the data. My friends with cateye and sigma systems tended to get runs of 4-6 months and I would get 3 yrs out of a specialized. All of these types in question used the same battery type.

my sigma is a wired model

I see what you mean, Im just trying to reconcile the data. My friends with cateye and sigma systems tended to get runs of 4-6 months and I would get 3 yrs out of a specialized. All of these types in question used the same battery type.

Now you've got all that clear, you might like to answer my question.

The battery? I misread the first post to mean new battery. My bad. :o

Any ideas on what to do? Give it a whack with a spanner? Believe me, I'm tempted...


If it's really dead, I recommend a BFH. Best tool out there-everybody should have one. A computer would probably crunch really well when hammered. Very satisfying!;)

At the car shop we have the BFH and the BFW. W being wrench of course.

At the car shop we have the BFH and the BFW. W being wrench of course.

What, no BFS? Didn't someone once say "Give me a big enough BFS and I can move the world"? ;)

What, no BFS? Didn't someone once say "Give me a big enough BFS and I can move the world"? ;)

Oh, I found it:

"Give me a place to stand and a BFS long enough and I will move the world”

Archimedes, 220 BC

Sorry folks been busy for a while... was stunned to see 30 replies...

Tried everything in the past few days, even asked the resident bike mechanic, who, after several attempts at minute repairs, suggested something slightly more violent than any of the BFS, BFW or BFH approaches.

However, my problem was solved when I was shopping for a new pair of knix this arvo, and saw a new comp on sale for $20. I'm sold. And it works fine. I figure I've got two years' worth out of that old computer. Who knows, I might even pull it apart and see if I can fix it from the inside out and attach it to my old BMX for a bit of fun.

Cheers all,

Binnsy

More problems...

The new computer I bought is a Techwell Mach 3...

According to the packaging, the odometer and total trip time are able to be set after battery replacement. Nowhere can I find instructions on how to do this....

Any ideas?

Binnsy

PS: I already tried the web site of the company but no email contact is listed....

Ummm... sorry Binnsy I think you pay for what you get. Who makes a Techwell Mach 3? And if you paid only $20 for it... well what can I say? No-one else wanted it at the original price, so the LBS put it in the discount bin.

I know Cateye instructions are a bear to deal with because they (as with most Asian bike part manufacturers) insist on publishing all those other languages, then have the important bits under one table, stuffed under the Spanish or Vietnamese or Russian section!

It must be there somewhere. Try setting the screen with the odo reading, then press the reset button (on the back?) and see if the far right odo figure starts flashes. If it does, one of the buttons on the front should change that number, the other moves to the number next on the left.

If not, then...

... throw it away and invest in something like a Cateye or Sigma that you know (a) has instructions that are OK (b) are reputable brands and (c) other people use and can identify with. A basic Cateye is only AUD$35, maybe $40. My old Cateye Velos have lasted three years on one battery.

Regarding Sigmas and weak batteries: my old BC800 would stop recording before its display went entirely bad. So I would have a perfectly working comp (accurate clock, working buttons etc) that just does not log speed or distance. Display would dim gradually during the last weeks, making it difficult to notice the weak battery. When LBS put a fresh battery in the difference in display was obvious and everything worked again.

--J

Sigma do identify the loss of display contrast as an indicator that the battery is nearly dead. At least in the instructions for the one Sigma computer I own. And it's true as portrayed by Juha's experience.

As one last observation, I am banal about keeping the boxes (wth bar and number codes) and instructions for the stuff I buy. Bike computers are one of the most important, coz if you throw away those instructions, how can you remember which way to reset the odo and wheel circ readings two or three years down the track?

Sigma do identify the loss of display contrast as an indicator that the battery is nearly dead. At least in the instructions for the one Sigma computer I own. And it's true as portrayed by Juha's experience.

As one last observation, I am banal about keeping the boxes (wth bar and number codes) and instructions for the stuff I buy. Bike computers are one of the most important, coz if you throw away those instructions, how can you remember which way to reset the odo and wheel circ readings two or three years down the track?

Wow, this was tough to find:
http://www.tech-well.com.hk/stockoffer.asp

This company, Tech-well, is a Hong Kong based mfg that makes some really diverse electronics products and it appears they did cyclocomputers for some time (now discontinued). Until these guys, I have found user manuals for every cyclocomputer that I looked for. Almost everybody keeps them on line today, if you just take a look. Most companies are catching on that it's cheaper just to post them on line than it is to mail one out every time a customer loses one.

Maybe, Binnsy, you can contact these folks and they can help you out, but I wouldn't bet on it as they don't make anything else for bikes ;-) I wouldn't be surprised if there were 50 million of these in use in China, though. Good luck! Here is their contact page:

http://www.tech-well.com.hk/contact_us.asp

Wow, this was tough to find:
http://www.tech-well.com.hk/stockoffer.asp


You bothered? Props to you.

Do you get the message, binnsy? And this, for heaven's sake, from a fellow Ozzie!!!!

You didn't really have to go to so much trouble...

But thanks anyway.... the email's on its way.

Meh, all I really need is something simple... I've logged most of my rides with odo readings anyway so it's not really much of an issue.

When I invest in a better bike (which should be in about 12 months) I'll probably go for a better and more widely-known comp.

Cheers all,

Binnsy