ETI SuperFast Thermapen Thermometer: On/Off Switch Fault




Introduction: 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:

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Step 1: Remove Batteries

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

Step 2: Remove Labels on Rear Case

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.

Step 3: Remove Case Screws

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.

Step 4: View of Opened Case

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).

Step 5: Close Up of 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.

Step 6: Clean and Lubricate

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.

Step 7: Reassemble and Test

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.

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    3 Discussions


    1 year ago on Step 7

    Thanks for posting John. Using your information, I was able to eliminate the angular dependent intermittant readings. Cheers!


    Tip 1 year ago

    This was very helpful in getting the Thermapen opened up, although I did not have a problem with the ON/OFF-switch. Rather, in my unit the display was flaky, usually only displaying a few segments but nothing readable. The effect would change when you twisted the unit, putting longitudinal torsion force on the housing, which would sometimes restore normal display for a brief time. So it was pretty clear that the display had a contact problem.

    By looking at similar ones on the pages of various electronics sellers I found out that this kind of display is usually not soldered in place but rather pressed against the contacts on the circuit board by metal latches which go through the circuit board and are then bent on the board's backside to hold the display in place.

    Now, as opposed to John KM's excellent description, you can really tilt the circuit board up on the side facing away from the sensor tilt mechanism. It is actually held in place by 3 of the housing screws which go through it, so when the housing is open it is just lying in there. The only thing restricting free movement are the sensor wires mentioned by John KM. However, those are actually rather flexible - really must be, if you think about it, as the part of them going through the tilt mechanism is being moved every time you tilt the probe in or out. You just need to be very careful to put as little strain as possible on them when you flap up the circuit board.

    So I went ahead and used a small pair of pliers to bend the above-mentioned metal latches a bit more so they would put a little more pressure on the board. I then reassembled the Thermapen and what shall I say - the display is working like a charm again, no sign of flaky contacts even when bending and twisting the housing (which is in fact very sturdy).

    Unfortunately, I did not take any photos as while I was doing all this I was quite uncertain as to whether it would work, but as it did I thought I'd add this tip here in case someone has a similar problem with their Thermapen. If you work carefully this is actually a pretty easy fix.


    2 years ago

    Great one, most people would throw it away as expensive as they are. Although TBH I think a folding one is a bit of a gimmick.