ETI SuperFast Thermapen Thermometer: On/Off Switch Fault

This is an excellent device while it is working OK, making fast accurate measurements. The unit is switched on by opening the probe out away from the body, but after about 3 to 4 years use, the on/off switch became intermittent, only switching on at some angles of opening.

I assumed the switch was a slip ring design and it had become tarnished or dirty, so I first tried squirting switch cleaning lubricant (e.g. ‘Servisol Super 10’ in the UK) into the rotating hub area, but this had no effect, so I guessed the switch assembly was sealed in some way. We carried on for some months until it became obvious that disassembly was required and, as I could find nothing on the Web to assist, the following shows how correct this fault:

Remove batteries and clip battery cover back in place (I found this makes reassembly easier).

Using a small sharp knife blade (I used a Stanley Throwaway Knife), remove all the labels on the rear. Take particular care in removing the large central label (as it contains some instructions) and place it somewhere safe and dust free, so it can be reinserted in place after reassembly.

Unscrew all six screws and then turn the unit over so you can carefully remove the top part of the case

Note: Do not try to remove the bottom part of the case (in the photo), as this houses the circuit board and you may damage the fine sensor wires from the probe.

Photo shows the case opened up, where you can see a sealing O-ring on the bottom part, (which explains why the switch cleaner failed to get to the contacts).

These photos show more detail of the poor state of the contacts, even though there seems to some form of white grease lubricant applied during manufacture. I can’t help feeling that the switch on this 2013 version needed some redesign work (possibly using gold plated contacts) and this may have been improved on current versions.

As the white grease may not react well with the new switch cleaner, I thought it advisable to start by removing it completely. Therefore, using a cloth saturated in switch cleaner, remove all the white grease and clean up the two contacts on the top case and the slip ring on the bottom case. I then lightly sprayed all contacts, including those that make contact with the circuit board assembly.

Reassemble in reverse order, insert batteries and test. Hopefully, all should now be OK.

Note: Switch cleaner doesn’t last forever and these contacts will probably need cleaning again sometime. Therefore, even if you have removed all the labels without damage, I would not refit the round one over the rotating hub screw, as I think it should be possible to remove this screw alone and use a knife/small screwdriver to prize the top case away from the O-ring far enough to insert the cleaning spray nozzle and spray the contacts again.