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Insight into the inside of the hearing aid

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Just opened this cheap hearing aid originally from Amazon:

HA_small

HA_large

HA_back

Another, this time more than just three transistors actually some complicated circuitry and ICs.
Both this and the one in the previous post failed because their NiMH rechargeable batteries died.

front
back
exploded

Yeah those don’t look to good in the quality department! But interesting how it’s all put together, very cheap Ni–MH batterys, nasty!

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I believe it is not going to be easy to replace this battery even if we find the right replacement one. In my Phonak M50r the battery is glued to the internal structure! What type of glue could it be? What solvent to use? Acetone? MEK? Paint stripper? Something else?

@gtremblay said:

my Phonak M50r the battery is glued to the internal structure!

Oh man it gets worse, using a solvent might damage the housing, you’d have to very careful doing that, what about some heat and some tweezers to help pry if off, I find it crazy it’s glued together, they obviously didn’t want it moving at all while wearing.

Edited

In reply to @sterei

Maybe plastic?

@sterei said:

I think these “nubbins” two are marks from the injecting tool’s pusher. These are pins used to push the part out of the mold after the plastic part was injected.

c3

@gtremblay Is the contact points (+/-) apparatus attached to the battery case or does it simply rest against the side of the battery case?

c4

In reply to @gtremblay

If it was me, I’d try mechanical separation with the tip of an X-acto blade or similar. Use some sort of apparatus that will hold the steady while you work, and use a magnifier. (Dental loupes are handy, but sometimes you need more magnification than their typical 3.5X. Some headsets go up to 14X.) The glue doesn’t have to be too tenacious to do its job. It may be that it was selected to allow re-work in the factory.

Also, that green stuff all over the battery wires and solder joint is some sort of conformal coating. It’s been awhile since I’ve messed with this stuff, so do a search to determine what you should use to clean it off before you do any work with a soldering iron. You’ll also need some more conformal coating to cover it all up after you’re done. It’s there for a reason, to keep the HA working reliably.

Another suggestion: To re-glue the new battery in place I’d use a dot of electronic-grade silicone. It’s likely not what they use at the factory (takes too long to cure), but it’s readily available (Amazon and others have it if you can’t find it locally). You want the electronic grade because it’s acid-free and won’t corrode. (Acetic acid gives the standard silicone its vinegar smell.)

The stuff sticks to near anything and should be easy to deal with if you need to get back in there.

@PVC They are maintained mechanically by 2 tabs on the battery casing (the small black part at the left on the photo).The tabs are integral to the battery casing. They are also “glued” to the casing by what looks like acrylic conformal coating.

@ctromley

1- As a magnifier I use my phone camera at 6-7 zoom. The phone is on a small table tripod. Problem with a glass magnifier is the focal distance is so short that it is almost impossible to work under it.

2- I believe your are right: the green stuff seems to be acrylic conformal coating.

3- Removing the complete battery with both wires appears too difficult (for me…) and re-installing the new battery even more difficult.

4- So I will try to remove both sides of the actual casing while protecting the wires. Then unsolder wires from the battery.

5- I will then slide the new battery (bare) in the old casing and glue the wire with electrically conductive glue.

6- Put the two plastic sides back into place and seal with a piece of thin plastic tape.

How about that plan?

In reply to @gtremblay

I have no experience with conductive adhesives. You’re on your own with that, but make sure you see the comment I posted while you were composing yours.

My main concern about conductive adhesive (which may be completely unwarranted) is that it may not like any movement whatsoever. Which is why I’m hesitant to recommend the plastic tape. Some electric grade silicone would do a better job of preventing movement of the battery and compromising the connection.

After some head scratching, I was able to remove the dead battery from its plastic casing. I also had to unsolder both wires. Doable but not easy. I will eventually refine the method…

Today, I ordered 6 batteries like that: https://www.alibaba.com/product-detail/M7854S1-3-7V-25mAh-rechargeable-hearing_1600227890083.html. I should receive it somewhere in december.

I hope it is going to work!

M7854s1/icr7854/lir7854 3.7v 25mah Rechargeable Hearing Aid A13 Earphone...14

M7854s1/icr7854/lir7854 3.7v 25mah Rechargeable Hearing Aid A13 Earphone Li-ion Battery - Buy M7854 Lithium Battery Tws Earphone Battery Hearing Aid Battery Coin Cell Button Battery Li-ion Battery M7854,Li-ion Battery 7854 Coin Battery Rechargeable...

Used the above URL, cut and paste onto Google bar to check the details. According to the spec sheet, the battery is able to last for at least 800 cycle charges (about 2.2 years).

Good luck.

From the coin battery website (China), there is a diagram with wire attached to the coin battery.Should ask them for assistance.

cell + wire

In reply to @DaveL

@DaveL said:

As I said, I’ve talked to many seniors who didn’t even know they had wax guards that needed to be changed.

I think the are a bit protected by the dome, itself! I have found my own double-dome silicone tips can be slippery feeling with some kind of wax, but the wax guard is UNDER the dome, so much less prone to getting plugged up - for the style of dome I wear.

As for changing the wax guard - say in a pair of Phonak aids? BWAAAAHAAAAHAAAAHAAAAAAA! It is such a torturous process I’ve actually given up! I figure if I go in once a year to see my audi, I’ll have HER do it, but honestly, it’s a total chore for anyone!

I can’t even get a grip on the flat, round disc to turn the dial to a fresh wax guard. Then, even if I get the new wax guard in position, it’s almost IMPOSSIBLE to punch it into place on the receiver. Seriously, my previous audi managed to punch TWO wax guards, one on top of the other, which I only realized a couple years later when I used a straight pin to pry them both out.

By contrast, my Oticon aids were SIMPLE to change the wax guards on, go figure. Phonak tech needs to buy a pair of Oticon aids and reverse-engineer the wax guard replacement.

I did what I described in my plan above. Since the battery plastic casing is glued to the structure by the conformal coating on about half of its periphery I decided that it would be less difficult to extract the battery from the casing and replace by a new bare one. As you see on the photos, the casing is still in one piece. To open the sides, I used a thin copper tubing heated with a propane torch.The sides are now bent at 90 deg. The two wires at still ok. There was also some coating around the wires inside the casing. It was not easy to extract the battery since it was sticking to its casing.

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If successfull, I will publish a more detailed description of what I did, if there is any interest.

Edited

if there is any interest? Wow!!!

Oh btw; This is the Phonak Marvel. Since the time of Marvel’s manufacture, Phonak has started on a new platform and the flagship model of that platform (the Phonak Life) has inductive charging. So it won’t have those two contact points (+/-) along with the rest of that charging apparatus attached to the battery case. I expect that other Phonak models will follow suit and also feature inductive charging.

Damn, that look really good.

I never ever dream to see somebody hack open hearing aids like this! Its normal thing in Sound Stereo system and Computer. But hearing aids!?

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