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powertap zero torque problem

Old 07-01-10, 07:40 PM
  #1  
forrest_m
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powertap zero torque problem

First ride after replacing the batteries in both the hub and the head unit. Tried to zero the torque, offset number was reading very high, 18-20. No amount of holding down the select button would make this drop any lower than 15, and the next time I tried it would be back up to 19 or 20. Tried numerous times during my ride today, with no appreciable difference. Tried holding it for ~3 minutes, no dice.

Any suggestions? Power would eventually drop to 0 while coasting, but sometimes it would take 10 seconds or more.

Needless to say I set all kinds of PRs today (read: power data from today = garbage).
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Old 07-01-10, 08:48 PM
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Did you replace batteries "just because," or were you seeing something strange (other than the blinking icon)?

I would recommend you pull all the batteries one more time, and see if that helps. Then, you start swapping parts with another PT setup. How's your Cervo like someone else's wheel? You wheel with their Cervo?

On the surface, this sounds like the failure I had a couple months ago that lead to a warranty rebuild. They think it was water (I ride in rain a lot -- this year anyway).
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Old 07-02-10, 10:19 AM
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Had a similar problem last time I replaced batteries, I think I used the 705's "calibrate" function in addition to fiddling with the batteries.
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Old 07-02-10, 10:54 AM
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Originally Posted by mattm View Post
... I think I used the 705's "calibrate" function in addition to fiddling with the batteries.

I was wondering what that does exactly. Does it tell the PT to "do" something or does it tell the garmin to "prepare" for incoming instructions.


thx.
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Old 07-02-10, 11:04 AM
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From what I could tell it's telling the PT to zero out.
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Old 07-02-10, 11:40 AM
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I figured the 705 calibrate was like taring a scale. If you're not pedaling, and the PT is reading like 7w, I figure the Garmin just resets to interpret 7w as 0.

But, I'm totally guessing.
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Old 07-02-10, 11:53 AM
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This is from the Garmin forum. It backs up what matt said.

"A change from previous Powertaps happened with ANT+, where zero'ing the torque offset was previously done while coasting, it is now done when stopped. The hub should auto-zero any time it is stopped, but the manual calibrate is there just in case."

hijack over.
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Old 07-07-10, 01:04 PM
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Just a follow-up. I called Saris customer service and they had me do a more involved self-test which determined that it was too far out of calibration and needs to go back to the factory. It is new enough to be covered by warranty and they are sending me a return authorization. Props to Saris for taking care of me, although it is still a bummer to lose my PT right in the middle of the season...
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Old 07-08-10, 10:43 AM
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Originally Posted by wanders View Post
This is from the Garmin forum. It backs up what matt said.

"A change from previous Powertaps happened with ANT+, where zero'ing the torque offset was previously done while coasting, it is now done when stopped. The hub should auto-zero any time it is stopped, but the manual calibrate is there just in case."
Where is this Garmin forum? I haven't found anything like that on their web site.
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Old 07-08-10, 12:43 PM
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Originally Posted by forrest_m View Post
Just a follow-up. I called Saris customer service and they had me do a more involved self-test which determined that it was too far out of calibration and needs to go back to the factory. It is new enough to be covered by warranty and they are sending me a return authorization. Props to Saris for taking care of me, although it is still a bummer to lose my PT right in the middle of the season...
I had that happen also. Long shot before you send it back - Did it get wet recently? Did you over tighten the cover when you put it back on? On a good note, their turn around time is excellent.
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