Polar T61 HRM transmitter dissection!

Well, after a couple years of faithful service, my HRM strap finally stopped transmitting. Unfortunately, it happened about halfway through A2A... Anyway, I know others have tried to replace the battery themselves without luck, but I started thinking of trying it anyway. After seeing the price to have Polar replace it ($30 plus shipping), I decided to give it a try. The first thing I found was Blake's blog entry suggesting to go in from the front. I also found forum entry on another site with a picture, so I knew what I was getting into:

http://www.timetriallingforum.co.uk/lofiversion/index.php/t10082.html

That forum entry also confirmed that Polar does replace the battery and return the original transmitter, so there must be a non-destructive way to get at the battery. So I puzzled over that for a while, then I got my heat gun... :)

Now, some of this way trial and error, so I think I could do a better job next time. But I think I have a pretty good idea now of how this is put together. Or, rather, how to take it apart in such a way that it has a good chance of being put back together. I saw what appeared to be a seam along the back of the monitor. I thought perhaps that the entire front might pop off, so I heated that up. A couple trim pieces at the top & bottom didn't really like that. Also, the front did not come off, but the back did quite easily...

After that, I tried many things to get the front to come off -- nothing worked. I heated various bits with the heat gun, tried slicing what I thought were important parts with a utility knife, still no luck. Finally, I had heated up one side (I thought I could get a screwdriver in there and pry it apart)... That's when the strap started to come apart from the center of the transmitter. I pulled harder and it came apart completely...

Now, I tried prying the circuit board out without luck (more on that later.) So I figured, okay, lets rip off the other half of the strap...

Now, surely the board would come out! I got my little screwdriver in there and the darn thing was being really stubborn. I could see the battery... I kept prying and suddenly the board came loose from the plastic!

In retrospect, I think all I needed to do was unscrew those 2 tiny screws in there! Ooops! It took me about 5 minutes to find one of them, but I did manage to get all the parts eventually...

After having done that, I'm not sure if it was even necessary to remove the straps from the center...

I do think a good way to get at the innards would be this:

1. Heat up one side of the center where the strap connects. Pull hard to disconnect it. Looking at the transmitter from the back, I think I would disconnect the strap from the left side.

2. With the strap disconnected from one side, it should be easy to pop the back of the transmiiter off. Just put a small screwdriver in the side and twist. It's possible that you might have to heat it up with a heat gun, but I don't believe at this point that it was necessary.

3. With a very small screwdriver, remove the 2 little screws.

4. Pry up on the little tab and separate the pcb from the plastic housing. Be careful not to damage the coil.

Sometime this week, I'll be heading to Batteries Plus to get a replacement battery. I'll post a follow-up and let everyone know if the transmitter lives through the operation!

- SM -