My history with SRM's is:
1. Wired Cannondale Si with PC-V, which worked flawlessly, all the time. I bought it second hand and later sold it to a friend.
2. Wireless Cannondale SiSl with PC-VII, which had dropout issues which I thought was due to my positioning of the magnet. I bought this new, but sold it to a friend earlier this year.
3. Wireless Rotor 3D+ with PC-VII, which I bought last year from the original owner. It won't connect to any of my Garmins - 800, 910XT, Fenix 2, so all figures are from my PC-VII.
I only spot this happening when I am accelerating up a hill and look down to check what power I am averaging- i.e. can I maintain this, should I push etc.
The power reading changes to zero, then "-", where it stays for a while, then it changes to zero again and finally back to (say) 326.
It happened today, but I didn't think to look to see if the cadence dropped out at the same time, but looking at the data in Training Peaks I can see that both power and cadence dropped to zero at the same time.
Looking at this, notice where speed increases up hill, with zero power and cadence:
This is, not to put too fine a point on it, driving me nuts.
Is it likely that this is a magnet placement issue, a reed switch issue, both or neither?
Also, why won't the SRM speak to any Garmin devices? My Cannondale ANT+ SRM did.
I've also got a P2M and a Powertap, and they a) both work flawlessly with no dropouts and b) speak to any Garmin.
I had this kind of trouble on the begining with my Rotor 3D+ and it would not pair with my Garmin. When I did solve the magnet placement problem, everything was OK
but if it happens in the same place on the road, the other possibility is a radar trap, the pc7 seems vulnerable to this, there're roads i ride where it'll drop out every time at the same place
while trying to isolate the cause i added a garmin, the pc7 dropped out but the garmin recorded without a break, i had the pc7 checked by srm, but they found no problem with it
It all got messy from there, with regards to refund vs unit replacement. However my solution (which I know does not help) was to refuse a replacement and move to P2M. Which has been flawless.
can you reproduce the issue in other locations? it could also be an ant+ interference issue, though that is pretty unlikely.
in this pic (130bcd spider) the two blue things at top right are the sensors, so ideally the magnet radius should bisect them, especially if it is mounted further away from the side of the pm
you could try spacers under the bracket, another way is get a rare earth magnet, 2x5x10mm is about right and put it on the end of the existing magnet - i did this when trying to figure out my own dropout problem
if that works ok, you can either rely on magnetism to keep it in place, or (degreasing first) put a blob on gel superglue on the face of the srm magnet then put the re one on, it'll be secure but with a bit of force you can still remove it if necessary
watch out if the chain gets dropped or is dangling during servicing, the magnet will grab the chain hard!
modern SRMs know whether they're moving forwards or backwards with their dual reed switches but i wonder what they do if the reed switches become "sticky". if one of the switches operates inconsistently or slowly then i wonder how it deals with that. could be some interesting error conditions. or it could be nothing
With a BSA shell that's going to take some doing- better to tape the magnet to the chain stay, or are there BB mounted magnets designed for this?
None of this answers the "why won't the SRM speak to any Garmin device" question, however!
February 17, 2014
SRM released a firmware update for PowerControl7. The new firmware improves the ability of the PowerControl7 to receive
PS: you might also want to take a look at their FAQ.
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