San Rensho 

I have a Ciclosport 124 C. It was working fine till I washed my bike today (that'l teach me). I took the display off the bracket before I washed it and when I put it back, the display was on but no cadence or speed. Cleaned all the contacts, re-booted the display, ran magnets directly on the sensors, nothing.

Should there be continuity through the wiring? There was voltage coming from the display unit.

Nycycle

Yes there is a pulse as the magnet passes the coil, also there should be low resistance across the terminals when tested. You may have damaged a wire, look close at the relationship of magnet to coil.
Hope this helps.

HillRider

Try drying the handlebar mount with a hairdryer. Water may have gotten into the contacts and is short-circuiting the pulses from the pick-up coil.

FWIW, my Cat-Eye's have been ridden in drenching rains many times and never suffered from water problems.

cascade168

I'm gonna disagree with this explanation. I don't know why people continually try to make this more complicated than it really is. No, there is no "pulse" and no, there is no coil. Wired computers use magnetically actuated reed switches. When the magnet passes the reed switch (i.e. the "sensor") it closes. It's a simple "open" or "closed" circuit. Period. To troubleshoot a wired sensor all you need is an ohmmeter. Meter the two terminals at the computer mounting bracket and pass a magnet by the sensor. The circuit should close with the magnet nearby the sensor and open when you take the magnet away. If you listen closely you should be able to hear the reed switch openning and closing. It will make a very fine clicking noise. If you meter the circuit and it never shows "closed", then you have either a broken wire or broken reed switch and the entire sensor/cable assembly will need to be replaced.

Wireless computer sensors use a Hall effect device which senses subtle changes in a magnetic field and they DO generate a pulse when the magnet is sensed. That pulse is transmitted, on a carrier wave, to the computer head.

cascade168

So, the short answer to your question is yes, there should be continuity between the two contacts on the head mounting bracket when you pass the magnet near the sensor (= switch). The voltage you see at the head unit gets passed along when the switch closes. It's as simple a binary circuit as there is.

The reed switch and two wires feeding it are typically potted in some type of plastic. If the cable gets tugged hard and one of the two wires separates from the switch, that's it. And, that's almost always the problem with wired sensors.

Rev.Chuck

All you need to check the computer is a paper clip. Bend it so you can cross the contacts on the back of the computer. cross them several times and see if the computer reads speed or cadence. Might take a try or two to get the proper pair of contacts.

Checking the wiring takes an ohmmeter.

You might just need to let it dry out for a day or two. Solid state can be surprising tough. My wife ran her keyfob car security gadget thru the wash. I took it apart and left the pieces to dry on a paper towel overnight. Put it back together and it worked fine.

cascade168

A great way to dry out this type of stuff is to let it sit in a gas oven (with pilots) for a few hours. Not too hot, and nice and dry. Nothing wrong with a little judicious use of a hair dryer either. As you say, these types of electronics are tougher than most people realize.

Wino Ryder

I would think blasting it with compressed air would work good, or the hair dryer trick. It would work faster than letting it sit in the oven with just pilot light heat. Not to mention the fact that you would have to remove the whole thing from the bike.

just my thoughts

HillRider

Good description of the way wired cyclometers really work. I guess I thought the pickup was a coil that generated an electrical pulse when the wheel magnet passed it rather than a simple magnetic switch. Thanks for the clarification.

San Rensho 

Thanks all, especially for the edifying explanation by Cascade on how these little rascals work.

I let it dry out overnight and today it worked fine.

Sheldon Brown

There should only be continuity when the magnet is next to the pickup.

Believe it or not, I have an article on this topic:

https://sheldonbrown.com/cyclecomputer-troubleshoot.html

Sheldon "VOM" Brown

Nycycle

Thanks for the disagree, I just went out and looked at mine, only my old one has coil at the bottom, my new ones I think are as you say, good idea too cuz that old one is a battery eater, and I don't think accurate.

Nycycle

I had an old one that was a coil, I discovered it when it failed I tried shorting across the wires, and metered across them (It was not removable), after my nephew and I looked it over we discovered it was a coil and magnet design.
When I got the new one I assumed it was the same, thanks to this thread I learned that all my new ones are just switches.

cascade168

I'm just curious how you made this determination. Every sensor I've seen has been entirely potted in plastic (or hard rubber, or whatever) and you usually can't tell just by looking at it.

Are you saying you actually carved it up and could see a coil of wire? I'd love to see a picture of your sensor.

Bill Kapaun

Ohm meter.
A switch will be open. A coil isn't AND may show a few ohms resistance to boot. And then you could measure the inductance.
How do you know Pluto exists? have you seen it?

Nycycle

cascade168This thing lived on an old Huffy that I had for since 83, give it to my nephew in 2004. he has like no money.
So when the speedo quit I tried to help him fix it. I did as you guessed, I cut it open to find a coil of copper around an rod. We found that when we touched the wires together as the bike store said, it did nothing, but when I put the ohm meter on it it did, I am going to see if it is still out in the shed, if it is I will photo it.
It did not have a quick release as the new ones do, wired solid, I think a wire pulled loose in the what I call a prox switch.


I now own 3 wired computers that do more than just speed, I assumed they were all the same, THANKS to you I went out and played with my new ones and now am educated.


I add this edit, nephew says we trashed it, but he reminded me it looked like a 5/16 bolt with no head, it was plastic and had threads, about an inch & 1/4 long, much skinnier than the new ones, and it came with a clamp.