# Garmin Edge 305 Speed Sensor Busted?



## zriggle (Apr 16, 2008)

For whatever reason, my 305’s speed sensor doesn’t seem to be picking anything up. Cadence, HR are fine, but no speed on the trainer. GPS is turned off. Pushing the little button on the Cadence sensor, the light comes on for the crank every rotation, but does not sense the wheel magnet. The magnet is still good (I was surprised how well it stuck to my trainer), and even if I take it off the spokes and move it with my hand in front of the line on the speed sensor, it does nothing.

Ideas?


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## ukbloke (Sep 1, 2007)

zriggle said:


> Ideas?


Try replacing the battery in the sensor. If that doesn't help, the next step would be to contact Garmin for support. Perhaps they will come through with a warranty replacement for you.


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## Kenacycle (May 28, 2006)

I wouldn't be surprised if your sensor is busted. I notice Garmin Edge products do not last very long. I had been using a Garmin 305 for almost three years and I have already replaced one sensor. 
Also, the GPS unit itself will start to go after about 3 years. You will notice it will occasionally shut off by itself and cannot hold a full battery charge for too long. 

My friend's heart rate monitor just died, and it's about 2 years old.

Garmin makes great stuff.. I love them,, I just wish they would make them last for at least 5+ years.


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## Mdeth1313 (Nov 1, 2001)

If the cadence is working, the speed should also work-- using those sensors when it's wet is a death sentence (I've killed about 4- hold your receipt, they're supposed to last a year, I keep sending them back to garmin). But, I've never had it where cadence works and speed does not. Sometimes if you go into accessories and restart the scan for cadence, it will pick up the speed as well, I'm sure you did this already, but check to see the magnet and sensor are aligned close enough to pick up the signal.

good luck- I had gotten so frustrated w/ it I wanted to switch to something else, but there are no other computers that suit my needs like the garmin.


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## joeyjmorales (Jan 12, 2010)

*speed sensor busted - fixed*

The good news: I solved this same problem. (symptoms: re-pairing, change battery and reset device do not work. Both green and red LED work but spoke magnet is not tracked by the GSC 10). 

The bad news: The fix is a hack (read on).

The magnetic switch inside the speed sensor arm is likely broken. It is called a "reed switch" (http://en.wikipedia.org/wiki/Reed_switch). It is an electronic switch that turns on when a magnet passes near it. Same type of switch used on nearly all magnetic bike speed computers.. This explains why the LED works but not the actual sensor when the spoke passes by)

I believe it breaks because the adjustable arm of the GSC 10 is flimsy and I when I ride outside, sometimes when I hit a bump in the road the GSC10 shifts and the spoke magnet will start to bang against the sensor arm on the gsc10. I believe if this happens enough it cracks the plastic case of the reed switch inside the adjustable arm. 

I called garmin CS and they said they hadn't heard of cadence working without speed - so I took my device apart, and tested it out. By removing the old reed switch (which was indeed cracked by the way), and touching the two wires directly together I see that it still worked. 

I replaced the reed switch ($1.50 part: http://www.sparkfun.com/commerce/pro...oducts_id=8642) and it is now working again. 

The problem: The plastic case of the GSC10 is not designed to be taken apart and repaired. I had to crack mine to get into it. Once it was cracked I had to rig it up with tape in order for it to work. It does work though but it is ugly!

I spend a lot of time figuring this out so here are some tips I already posted in the Garmin Support forum. I hope someone reads this: 

1.) The reed switch used in the GSC 10 is not very sensitive to magnet. I replaced my broken reed switch with one that I salvaged from a cat eye sensor. The cat eye reed switch is much more sensitive to magnetism with a slighly larger range.. This is important becuase if the reed switch is more sensitive, the sensor arm does not have to be positioned so close to the spoke to trigger and is thus less likely to shift and hit the spoke (which is what I believe caused mine to break). 

2.) I know this problem must be common because the exact same thing has happened on two of my devices and I have fixed both of them the same way. It would be very useful if I could repair this without breaking the casing. I have already spend 120 on my two broken sensors - so I will continue with my duct tape fix until garmin improves the design or one of the other ANT+ compatible companies develops a speed/cadence sensor. Bontrager has a nice ANT+ speed cadence but it appears that it only fits certain bike frames. Garmin is still most viable option but I have my eyes open until it is made more reliable.


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## ukbloke (Sep 1, 2007)

I suppose there must be two reed switches in the Garmin sensor - one for speed and one for cadence? There has to be since there are two separate magnets and two separate things to measure. It seems plausible that either one could fail with the other continuing to work. I'd try Garmin support first as their warranty is excellent. Even if out-of-warranty you might be able to convince them to send you a new one by arguing that it is a design issue or quality defect.


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## Kenacycle (May 28, 2006)

Joe,

Thank you for sharing your finding. Could you post some pics of your sensor in it's current repaired form? 

thanks


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## joeyjmorales (Jan 12, 2010)

Hi ukbloke, 

Presumably you are correct that there are two reed sensors. The first one would be in the main body where the cadence magnet passes. The second one (for speed) is located in the adjustable arm. 









I believe the reason speed seems to break more than cadence (in my small test case of 2 devices with 100% recurrence of the problem), is becuase of how close the adjustable arm must be placed to the spoke. This is why I commented (on garmin forum) that a stronger reed switch would allow you to place the arm farther from the spoke in a safer position...

Admittedly I know my spoke has hit my sensors rather hard and this has probably caused the issue - but with the new reed switch I put in myself I am able to place the switch at a much more reasonable distance and it is now working better despite the fact that it looks hideous. 

I do recomend anyone with this issue contact Garmin first before using my work-around. I also contacted Garmin and they said they would replace it if I had a receipt proving it to be less than one year old. Unfortunatly mine are about 15 months old and thus out of warranty and Garmin saidthey will not replace them. Unfortunately I didn't notice all summer (which would have been < year) becuase I was outside and thus using GPS based speed. Now that it's winter and I'm in the basement/trainer I find myself in this likely situation.

because of the particular angles and position of the sensors I'd hypothesize that it would be much less likely for the cadence sensor to break. Perhaps it is just my bike geometry though...


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## joeyjmorales (Jan 12, 2010)

Sure Kenacycle - I agree with ukbloke. This should be a last resort as you have to break the case to do this. Before trying this make sure you have:

1.) Try to replace battery
2.) Re-align to spoke and re-scan for the device
3.) Try to contact garmin support to see if they can either help or replace it..

If all else fails and no matter what it does not work.... Then have at it.. It is already broken anyway! Here is my first round and it's working great...

Step 1: Unscrew the adjustment arm so you can see how the wires are attached (be careful not to clip the wires while removing it)

Step 2: Open the arm and detach wires from existing reed sensor. You will have this: 









Step 3: Examine old reed switch so you know what this piece looks like when searching for a replacement. (The magetic switch device is somewhat obvious). 

Step 4.) Either buy a new reed switch or get one from an old device. Mine from an old cat eye worked fine. 

Step 5.) Connect the two loose wires from GSC 10 to terminals on new reed switch. You can be as sophisticated as you want here but I just twisted them and taped them which is probably the biggest slacker appraoch - but it works. I marked the location of the reed switch with pen so I know where the magnet needs to pass...


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## joeyjmorales (Jan 12, 2010)

It's in the last post.. (forgot to reply to you)


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## crj (Jul 31, 2006)

zriggle said:


> For whatever reason, my 305’s speed sensor doesn’t seem to be picking anything up. Cadence, HR are fine, but no speed on the trainer. GPS is turned off. Pushing the little button on the Cadence sensor, the light comes on for the crank every rotation, but does not sense the wheel magnet. The magnet is still good (I was surprised how well it stuck to my trainer), and even if I take it off the spokes and move it with my hand in front of the line on the speed sensor, it does nothing.
> 
> Ideas?


Just happened to me, first time on a trainer with the Edge 500 no speed registering, cadence fine. Found a replacement on ebay for less than forty inc shipping.


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## edgar55 (Feb 10, 2011)

*garmin sucks*

Just rang Garmin with the same problem, busted reed switch. They said they will not send me a replacement as the unit is outside the warranty. The guy insisted that it was my private opinion that this was a design fault and that they did not come across this problem frequently. What a waste of money!


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## beep500 (Jul 12, 2013)

*Fixed mine too*

Thank you internet.

Mine had the same problem. Red light blinked, green light not blinking. I think the magnet got knocked in and started hammering the pick-up too much and killed it.

I just fixed mine. Replaced the reed switch and used epoxy to seal it back up. Not so pretty but saved me $60.

thanks all very much all.


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