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PostPosted: Tue Mar 05, 2013 7:28 pm 
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Joined: Fri Aug 12, 2011 11:58 am
Posts: 5
Hi everyone!

I bought a used 5-year old SRM Dura-Ace 7900 power meter. It's been used only about 500h by a pro cyclist few years ago.
Anyway, when I first time did the zero offset, the value was 6500 +-10, so pretty stable, but the reading was insanely high!
Well I didn't mind and went for a ride. The power seemed to be way too low. Went back home, did a calibration check with a 10kg weight and changed the slope from 19.6 to 16.1.
After that I went out again, and the readings were somewhat normal. At least I think so. Did few sprints and the max power was about the same I knew I could do.

So do I have a problem here? Should I send it to SRM or just leave it like this _if_ it works well? Only one (or actually two) ride(s) done.

Thanks for your help.


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Posted: Tue Mar 05, 2013 7:28 pm 


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PostPosted: Tue Mar 05, 2013 7:46 pm 
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Joined: Fri Dec 24, 2010 9:37 pm
Posts: 537
Location: it's raining, it must be uk
5 years old, with original batteries?

assuming it's using the ltc-7pn, according to the spec. sheet an isolated battery has c. 10-year shelf life, there must be more drain than that even in an idle srm so it's probably due for some new batteries and a calibration


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PostPosted: Tue Mar 05, 2013 8:09 pm 
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Joined: Mon May 22, 2006 8:18 pm
Posts: 521
Location: Netherlands
When you have an SRM, you should be able to say more than "max power was about the same I knew I could do."
I understand what you mean, but I'd send it in. Then you can check your own calibration method against the factory-calibration. It's worth it.

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PostPosted: Tue Mar 05, 2013 10:13 pm 
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Joined: Tue Jun 06, 2006 4:35 am
Posts: 137
Kraaf as sungod mentioned maybe it's the batteries and a second opinion check the magned maybe it's not in the right position.

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PostPosted: Tue Mar 05, 2013 10:40 pm 
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Joined: Fri Jul 23, 2004 8:24 pm
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Location: Houston, Texas
If you are mechanically inclined and know what digital VOM stands for, since the SRM is way out of warranty, I suggest that you pop off the back cover and measure the voltages of the batteries and compare to the spec printed on the label of the battery. If the measured voltage is more than .25-.35 volts below spec, time for new batteries.

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Posted: Tue Mar 05, 2013 10:40 pm 


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PostPosted: Wed Mar 06, 2013 3:45 am 
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Joined: Mon Oct 10, 2005 9:23 pm
Posts: 171
And make sure you measure the battery voltage when it's under load. I think turning the SRM on by waving a magnet by the reed switch will do.


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