I bought a couple of handy digital thermometers with fold away probes a few years ago, in a local sale.
They’ve been fine, and despite their long metal sheathed probes, are able to detect warm breath if blown on from over a foot away.
Better still, they’ll run from a AAA NiMh cell, rather than a lithium coin cell, which needs to be replaced whenever it dies. I recently bought the new version (another sale), and was disappointed when I discovered it DID want one of those things, and had lost the folding probe too. On the other hand, it still used that great sensor.
Then, one spoiled the fun when its multifunction power button started acting up – it should be: press to switch on, press again to activate the Hold function, then again to release it, and then press for a few seconds to switch off. But, the button became erratic, failing to make contact, and delivering those options at random – if it even made contact at all. I had to resist the urge to press TOO hard, and maybe damage something.
When I tried to open the thermometer to fix this, I got a couple of surprises.
First, when I tried to split the case to get inside, I (fortunately) didn’t try too hard. Expecting the usual plastic clips, I discovered it was properly made, and was held together by no less than SIX screws, which had been hidden behind the front panel that had been held in place by adhesive tape, easily defeated with no damage after a little heat had been added.
The second surprise was the type of switch I found inside.
I’d been expecting a variant of this design, which has become common in recent years inside almost every electronic device out of China, and either works forever, or fails quickly.
I don’t know how many I’ve replaced, and probably have around 100 in a drawer.
But, I was wrong, and it turned out I didn’t even need a replacement part.
It is possible to split the type seen above, and clean the contact area, which is usually the problem if it’s become contaminated – my small ultrasonic baths like to kill them, probably because of the damp atmosphere they create inside their cases.
However, in this case I found a pair of switches made from these discs.
It took me ages to find them, and almost gave up, before I spotted a pic with ‘Metal Dome Switches’. I had been trying variations on the ‘Tactile Switch’ description that find the above style.
I had expected it to work, or at least get me close, since these discs are just the switching part used in those push switches, without the supporting body.
I’m not sure what happened to the faulty one, since it was fine when cleaned and inspected, and worked fine when the thermometer was reassembled.
It looked as if a miniscule piece of dirt had landed on the dimple in the centre, preventing it from making contact when the button/disc was pressed, and all I had to do was push it off. It wasn’t even stuck to it.
I’m surprised the usual repair strategy of ‘HIT IT’ hadn’t dislodged it earlier, but it just might have been too light to be affected.
I think I was maybe also lucky these discs were not stuck in place using Kapton tape, which is often laid over them to hold them in place, together with the small locating pins on their edges. Removing the tape and its adhesive can sometimes be a hassle.
Although, if they had been assembled with tape – it could have prevented any contamination from getting under the disc.
🤔