Tear Down of IR Thermometer (testo 845) - Page 1
Forum section: electronics / repair

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 17, 2014, 10:05:39 am
content: Hello,I can't tear down the IR Thermometertesto 845. It's faulty and I would like to repair it. I bought it very cheap on eBay althought it's a very expensive one (recommended retail price: ~1600US$):Here a video where I try to explain the problem:I can't explain myself how this thermometer was assembled. I already bent the housing very hard and i'm pretty sure it will break when I bend it harder.I don't think the parts of the housing are glued together, because you can send this device to the manufacturer for repairing (too expensive for me and makes no fun).I believe there must be a trick.I can't find any service manual.

author: Rasz
author_rank: Super Contributor
timestamp: September 17, 2014, 04:30:40 pm
content: you pretty much covered all the baseshmm, do you know any dentists/vets? xray could help

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 17, 2014, 04:51:22 pm
content: Quote from: Rasz on September 17, 2014, 04:30:40 pmOften I can't see the forest for the trees; maybe I missed here somethingQuote from: Rasz on September 17, 2014, 04:30:40 pmThats a really good advice! Unfortunately not; I know an engineer of xray machines, but he retired two years agoI bought this faulty and unbreakable thermometer ... what have I done?!

author: simplifyiyuk
author_rank: Contributor
timestamp: September 17, 2014, 06:43:29 pm
content: I'd say the back needs to come off before the sides. perhaps there are some hiding screws above the screen or a clip that comes unclipped when inserting a shim into the slot below the screen.have you tried sliding any parts up or down instead of levering away from the case.lost count of the amount of gear I've given a brutal beating only to discover they slide or unclip with a shimgood luck

author: Shock
author_rank: Super Contributor
timestamp: September 18, 2014, 11:38:24 am
content: Shine a good light in the holes and see if there are more concealed screws your missing.Especially where that sensor is there could be a screw way inside there, it looks like the plastic is anchored there. Check the battery compartment looking upwards as well.It makes sense the sides come off as where there are electronics between parts they have to run wires, so lifting the back off would involve some long looms which is unlikely. For that same reason I don't believe the LCD panel should be removable that way. I would think it would be fixed by screws or clips to a PCB on the inside.Also look along the seams for breaks in the plastic indicating pressure points.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 18, 2014, 11:51:00 am
content: Can you take the optics out? Maybe you can take off the little knob that is used to focus and it will come out?

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: September 18, 2014, 07:50:51 pm
content: There is a slot in the metal frame just below the "print" button which exposes a piece of the plastic casing.To me it looks like some sort of lock mechanism.If my theorie is correct, you should be able to push the protruding piece of plastic inward with a big flat screwdriver.While keeping it pushed inward you should be able to slide the metal frame upward or downward.

author: karkera
author_rank: Contributor
timestamp: September 18, 2014, 11:14:03 pm
content: Hi,I did go for FLUKE.... reliabilityRegards

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 19, 2014, 03:02:40 pm
content: The Metal Frame:On the image 01a I inserted two cards inside the frame as far as possible. Above the Mode button there is an area where you can't slide the card anymore. I believe there must be a clip or screw! On the image 01b you can see the gap between the cards; no clips on the surface are visible.I can also insert the cards inside the frame on the top (image 02) and lift the frame a little bit; you need a lot of force to lift it up; you can see screw driver marks on the plastic. When you remove the cards, the frame slides back again.

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 19, 2014, 03:26:05 pm
content: Quote from: simplifyiyuk on September 17, 2014, 06:43:29 pmIt's very good advice! I tried it out now, but unfortunately nothing slides in any directionQuote from: Shock on September 18, 2014, 11:38:24 amYes I tried that out and found a screw! Unfortunaly I can't see what this screw holds and I can't remove it; it's deep inside the hole.Quote from: Shock on September 18, 2014, 11:38:24 amYou can't see inside; the batteries puch against a wall.Quote from: Shock on September 18, 2014, 11:38:24 amThere are no breaks visible along the seams.I can slide a card along all seams some millimeters deep.

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 19, 2014, 03:44:03 pm
content: Quote from: PA0PBZ on September 18, 2014, 11:51:00 amI have the feeling that the optics are set in concrete; you can neither move it nor rotate it; it's also absolutely free of clearance. Very good qualityI can't remove the knob. Maybe there are two parts, which are glued together?

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 19, 2014, 03:51:06 pm
content: Quote from: sunnyhighway on September 18, 2014, 07:50:51 pmSorry, I forgot to mention that on the video. You are absolutely right, itlooks likea lock mechanism and I also thought that, but it's just a gap where the plastic frame for the LCD slides in. You can see the frame on the table in the video.

author: Shock
author_rank: Super Contributor
timestamp: September 20, 2014, 09:52:08 am
content: Quote from: medvedev on September 19, 2014, 03:26:05 pmProvide more info and show clear shots of the screws position. Even take several shots from all angles into the hole may reveal how it's put together.Can you see the screws head? What is the reason you can't undo it? What direction is it facing (it will tell you if the screw needs to be removed now or later).I also noticed in your video you placed a lot of emphasis on removing the back. I'd be looking at taking the screw out first if you can then see if a side comes off. If a side does remove it may even be the one opposite the slider.Also there is a chance that the trigger is put in last. So carefully without damaging it see if the trigger somehow pops out.Lastly if there are some clips holding the two side halves together you may be able to pry them apart from the bottom of the handle but this is very last resort so do so at your own risk.

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: September 21, 2014, 11:44:07 am
content: There could be some screws behind the "trigger" button.Maybe you could partially flip out this trigger button by bending the two halves apart and lift the trigger at the green arrow.Be careful while doing this because I suspect two pins on this trigger (red arrows) you don't want to break.Further more, you could try to wedge a flat screwdriver or plastic card at the location of the yellow arrow wiggling downwards towards the trigger.I would expect some sort of clip there or a little bit more toward the trigger button.ADDED:I noticed a second start point where you could insert a flat screwdriver or plastic card and wiggle your way down (yellow arrow second photo)

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: September 30, 2014, 08:03:00 am
content: I opened it!AsShock&sunnyhighwaysuggested I tried to remove the trigger; suddenly I heard a crack from inside and a clip fell out. 10 minutes later I could remove the right cover.The cover are held by a bunch of internal clips(red circles), two of them are now broken. A lot of screws are holding in place the thermal unit.The metal frame around the LCD is held by screws on the bottom (together with the PCB) and with solid metal clips on the top(blue arrows). The frame is not just a sheet of folded metal, I think it's cast metal; anyway it's very solid.Note there is no puch button for the trigger! Insteas testo uses a reed relay(pink circle)and the magnet sits on the trigger!In the next couple of days I will try to repair the thermometer; the display always shows that the temperature exceed the measurement range (too hot).