Hi,
I finally broke down and opened one up.
I've actually been curious about what's under the bubble for a couple of
years, but I never knew how to take them apart.
So curiosity finally got to me tonight and I resorted to brute force.
I used a miniature screwdriver to start opening it at the notch in the back
end of the card, looking for some kind of a "snap-in" catch. Instead, it
turns out that the top layer of plastic is held in place by some
double-sided tape which is really very strong.
There is no chip-circuitry under the bubble; the black plastic card-edge
contains all of the chips (so be careful with the black part !).
Instead, under the bubble there is just a battery sitting in a formed
recess in the plastic, with 2 spot-welded strips of metal connecting it to
the cartridge. It appears to be something like a "CR2320" by Panasonic,
but I can't really tell because part of the model number is covered by a
spot-welded strip. The final part ("320") of the model numebr is clear
however. My multimeter tells me that it's 3 volts. I'm pretty sure this
is a common variety.
I know that some people were talking about their Ten No Koe cards dying
because the batteries inside had died.
But I think this should be pretty simple to replace, if you are handy with
a soldering iron.
The tricky part seems to be removing the bubble part without scratching or
breaking the card, and then putting the bubble back on neatly when you're done.
- Dave