Alas, the day has now come when I too must ask a question, and can bask in the wisdom of my Bike Forums peers.

I seem to be having a problem with my computer. I don't really know exactly what's wrong, so I definately don't know how to fix it. A couple of days ago, I was tooling along at a good 22-24 mph, when I glance at my computer, and just for a second it reads "11 mph," then goes back to 20ish. This happens again every 15-20 seconds. I wrote it off as just weirdness, but it happened again yesterday. Every 20 seconds or so it would flash 9, or 10, or 13, and then go back to actual speed. Has anyone else had this problem? What gives?

I'm using a Sigma Sport BC 1200 that I've had for about two years, and I've never had any problems before. Is the computer trying to tell me something? Is the battery dying? Perhaps the sensor doesn't pick up on every rev (this actually occured to me about 30 seconds ago, so I haven't had a chance to test this theory)? In any case, if anyone has a suggestion, I'd very much like to hear it.

Thanx!

Sounds like misalignment somewhere--in some cyclocomputers, the magnet has to pass very near the pickup, too: so a bit of wobble could cause it to miss now and then.

With wireless computers (I don't know if yours is or not), radio frequency emissions, especially in industrial districts, sometimes cause misreadings. This happened to me once, but only once, with my Cateye wireless.

I would put the bike on a stand (if I had one) or rig it up somehow so that I could turn the wheel by hand for a while and check things out.

Good luck....

Lightboy,
I think its time to buy a new cycling computer, using it for two years has already outlive its usefullness and don't argue that it has a sentimental value, its time to replace the old computer (cycling computer)

Coincidently, I had the exact same problem recently with my Cateye cyclocomputer. I was thinking that maybe it was because of the rain.

I could tell that the computer was showing two speeds. One appeared correct and the other was too high. Was this your experience too?

Were you riding in wet conditions also?

Lightboy,
I have a Sigma 1200, too. I had a similar occurence with the cadence count. 0, 90, 40, 60, 0, 0, etc., then 0, then bouncing around again. I checked the funky little connector, which is always coming loose, taking it off and plugging it back on several times. Cadence still bounced around then settled at 0. Took it to the shop. They said the connector was just loose. It was fine after that. I left scratching my head. Are the mechanics just better at plugging a wire in than I am? The front pickup occasionally stops registering. Usually the magnet has shifted or been knocked. 1 mm can make a difference.

Regards,
Raymond

Tiny metal fragments from the road sometimes stick to the magnet this causes some wild things to happen, other than that sounds like battery, or its getting to hot,

I thought of something else, reminded by Raymond's experience with the loose connector.

I took my bike in for something unrelated to the cyclometer, and when I got it back I noticed the mechanic had put some kind of waterproofing sealant that resembles putty, but is solid, over the semi-exposed connectors of the computer. I hadn't asked for this, but was glad to see it.

Could you have got some moisture inside your computer?

Fixed it! At least I think I did.

I wanted to see if the problem was in the computer, not the magnet, so I threw my other wheelset on and took it for a ride. I didn't have a lick of trouble in 40 miles. Therefore, now that I have done some creative fiddling with the magnet on the problematic wheelset, it should fix all my problems.

Thanks for all your help!

Thanks for bringing up the subject and thanks for posting your found solution.

I was having the same trouble, but never thought to bring it up.

Glad to see the problem solved!

Just remember, though, if your cadence reads "zero" sometimes, it may not be the computer at fault--check to see if you're forgetting to pedal....

OK, I'll throw my two cents in.

I have a Cateye Astrale and have seen this problem. It wasn't the magnet. It was the contacts on either the back of the computer or handlebar mount. I guess they were tarnished, corroded, or something. When the speed showed an obviously wrong number, I'd wiggle the unit in the mount and -- presto, it would start working. Of course I would forget to look at it once I got home so the problem plagued me for a few weeks.
I finally remembered to check it and cleaned the contacts on the handlebar mount and the computer with fine emery cloth and it seems to have corrected the problem.

Ron

Aha! exclaims I.

My computer's a Cateye Mity-something. And above I posted about what the bike mechanic did (unasked but appreciated) about the hookup. Maybe because he knew about a similar problem? I never thought to ask.

Anyway, with the place where the wires come in, sealed, at least I have not had one single problem.

Servus,

Since everybody else said somthing...

Ron mentioned cleaning your contacts with a fine emery paper. I reccomend using an eraser from a new pecil. That's what the commo guys used to tell us to do when the handset on our blindingly expensive radios wouldn't work. Worked like a charm, every time. I clean my comp contacts every time I wash the bike, as our water system is heavy with calcium and sometimes the buildup causes erratic operation.

Another factor for erratic performance could be where you are in relation to high-voltage lines. My HRM does funky stuff in the city because of all the power lines for the street cars. According to my HRM one day, my pulse rocketed to 259 and then dropped instantly to zero. After checking my carotid to detrmine that I was still alive, I noticed the wires. I moved away and , bingo - problem solved.

Hi guys, just for the record,If you ever want to check out if the censor is working and picking up the magnet..listen to it in a dead silent room..it makes an audible click as the magnet passes by it, this "click" is the tiny reed switch in the censor opening and closing..this proceedure comes in handy for determining what is wrong sometimes and thus narrowing down possible causes for faults...-Buddy.

When all else fails, check your wiring:

I experienced a similar problem last summer with my Specialized Speedzone... I rode home from work, and upon retrieving my ride data, I was delighted to see that my AVG speed was 34.8mph, and my TOP speed was 84mph! Wow!

Unfortunately, I was not suddenly bionic. No, I had noticed that the speed display would vary greatly as I watched it... 11, 25, 16, 0, 0 ,0, 12... and so on. Also, my 17.3 mile commute had whittled down to just over 11 miles.

I repositioned the magnet: NG. I replaced the magnet: NG. I removed the computer and burnished the pickup buttons in the mount and on the computer: NG. I slapped my face like Curly of The Three Stooges, then swapped the computer head with the one from my rainbike... also: NG.

Then I noticed that by moving the handlebars back & forth while the bike was stationary, I could get the computer to start to count....

Hmmmmmmmmmm.... Another Curly slap for good measure, and found that the computer pickup lead had been chafed raw by being pinched between a cable housing and the bottom edge of the head tube. A little Exacto blade work, a bit of black tape, a zip tie, and... fixed as new.

Those bogus figures, 34.8/84.0mph, were a tremendous and very pleasant... if perhaps fleeting... surprise.

Now there's a problem that doesn't occur with wireless ones!