Surgery

 "Tentative efforts lead to tentative outcomes.  Therefore, give yourself fully to your endeavors.  Decide to construct your character through excellent actions and determine to pay the price of a worthy goal.  The trials you encounter will introduce you to your strengths.  Remain steadfast and one day you will build something that endures: Something worthy of your potential." - Epictetus

Yesterday I was doing some steps on the elliptical, looked down, and noticed that the heart rate monitor was reading zero.  That seemed a bit odd, because near as I can tell, I'm not dead yet.

The heart monitor is a vintage Polar A3 that I picked up cheap at auction.  The big digits were showing a couple of dashes.

 When I first got the heart monitor, I replaced the batteries in the wristwatch, but not the chest strap transmitter unit.  That's because replacing the transmitter battery is quite a bit of trouble, and it was still sending signals to the wristband.  With the heart rate signal gone, I figured it was probably safe to assume the 20-ish year old battery in the chest transmitter was toast, because the wristwatch display was still displaying the time. 

The user manual says to contact Polar for a replacement transmitter.  Polar probably doesn't even support something they stopped selling 16 years ago.  I decided replace the battery myself - and I've done this before - it worked out OK.  It's just a tedious process that takes 15-20 minutes to replace one coin battery.

The back side is pretty well sealed up, but that's how you have to go in.  The textured bits off to each side are the electrodes, which contain gold foil and conduct the electrical signal across your heart to the transmitter in the center.

The transmitter (and battery) is underneath this oval-shaped seal.

I use a heat gun to soften up the plastic, but it's still quite a challenge to get into the case.

Once you manage to get the back off, things go pretty quickly.  The circuit board has tabs on each side that connect to the side electrodes.  You have to heat up each side where the tab is inside the strap, and gently pry the tab out from underneath the plastic.  It's impossible to get the circuit board out without first heating and softening up the hard plastic.

Yep I had to pry it out with a screwdriver, one side at a time, after heating it up.  It's stubborn.

Below, the other side of the transmitter. 

Below:  The offending battery

Below: Once you have replaced the battery and re-installed the transmitter in the chest strap, you want to verify that it made connection with the electrodes before sealing the unit shut.  That is not my resting heart rate.  That is my grumpy "I'm freezing my ass off in a 45 degree shop" heart rate.

Below:  Closed up with a glob of clear silicone sealant.  It ain't pretty, but it works and has a new battery.

Below:  Post-op care while the sealant cures.

Below:  Done!  Not as clean-cut as a couple others I've done this with.  I should have cleaned the sawdust off the clamp.  All I care about is that it works and that sweat stays out of the electronics.