Repair of Sennheiser Momentum True Wireless earbuds
I have a pair of Sennheiser Momentum True Wireless (MTW3) earbuds that had been lost for a while. Once I found them, they had been laying around for a while and the battery was completely drained. I tried to charge them, but they did not charge at all. They are completely dead.
Here they are.
What I could see, there was no obvious way to open them up. I could not find any screws or anything that could be used to open them up, so I used my hot air gun to heat them up any potential glue.
That made the trick.
I located the battery and measured 0.910V. That is very low for a lithium battery. My guess is that the charge circut cut off the battery due to low voltage.
I connected the battery directly to my to my lab power supply. I set the voltage to 3.7V and the current limit to 0.1A. I charged for a minute or so, then measured the battery voltage again, now it was 3.7V.
I put the earbud back together and then in the charger. Now it started to charge. Phew.
I did the same procedure for the other earbud and now they are both working again. I used hot glue when I put them back together so they are easy to open up when I lose them and find them next time.