Author Topic: Fluke 287 Input Alert Diode Type / Replacement  (Read 11598 times)

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Offline JohnS8Topic starter

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Fluke 287 Input Alert Diode Type / Replacement
« on: May 31, 2015, 06:45:59 am »
Hi,

I've bought a used Fluke 287 on eBay that has an issue with the input alert ("Leads connected incorrectly" in any setting right after boot). Visual and initial inspection revealed (so far) that the diode (LED?) between the A / mA sockets (labelled DS2) is missing. Probably the solder joints were bad and/or the device was dropped ... unfortunately the missing diode is also not found inside the case of the multimeter.

So far I tried using a white status LED (the only kind available for a try). On power up it blinks once quite brightly and as soon as the input alert goes off it flickers with a couple of short blinks / second. Apparently my replacement is not the right kind as the input alert goes off despite the operating LED.

Does anyone have a suggestion as to what kind of LED I could try replacing it with. As I have no working unit I can't say which color or wavelength the diode uses (maybe even IR?). I would really appreciate any feedback or if another owner can identify what LED is used inside a working unit.

Btw: In the pcb picture posted by Baqar79 the diode DS2 is visible (between the amp sockets)
https://www.eevblog.com/forum/reviews/fluke-287-dmm-teardown-and-photos/?action=dlattach;attach=11258
 

Offline JohnS8Topic starter

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Re: Fluke 287 Input Alert Diode Type / Replacement
« Reply #1 on: June 11, 2015, 08:11:57 pm »
 :) Problem solved ... with a little reverse engineering: Fortunately the phototransistors are quite unique and easy to identify as OSRAM SFH 325 FA-3/4-Z series, peaking at 980nm wavelength, and that gives a clue about what kind of LED is being used in the input alert circuit. For reference if anybody ever comes across the same issue:

The Diode DS2 is an infrared diode. Replacement with an SMD 0805 sized IR diode with 940nm wavelength seems to work just fine. In my case a Harvatek HT-170IRAJ was used. Just be careful that the height of the led is not to great, otherwise the diffusor in the multimeter case will crush your led when the case is reassembled  :-+
 
The following users thanked this post: romantronixlab, zinom

Offline ModemHead

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Re: Fluke 287 Input Alert Diode Type / Replacement
« Reply #2 on: June 11, 2015, 08:51:20 pm »
Useful information.  Thanks for coming back to post the results of your search and successful repair!  :-+
 

Offline Binhnt

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Re: Fluke 287 Input Alert Diode Type / Replacement
« Reply #3 on: August 20, 2015, 03:26:27 pm »
:) Problem solved ... with a little reverse engineering: Fortunately the phototransistors are quite unique and easy to identify as OSRAM SFH 325 FA-3/4-Z series, peaking at 980nm wavelength, and that gives a clue about what kind of LED is being used in the input alert circuit. For reference if anybody ever comes across the same issue:

The Diode DS2 is an infrared diode. Replacement with an SMD 0805 sized IR diode with 940nm wavelength seems to work just fine. In my case a Harvatek HT-170IRAJ was used. Just be careful that the height of the led is not to great, otherwise the diffusor in the multimeter case will crush your led when the case is reassembled  :-+

Omg, thank you so much John, i have the same situation with my fluke 289. i got to do as your recommendation.
Very great job man !
Saigon, the farest pearl.
 

Offline JohnS8Topic starter

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Re: Fluke 287 Input Alert Diode Type / Replacement
« Reply #4 on: August 22, 2015, 09:45:43 am »
[...] thank you so much John, i have the same situation with my fluke 289. i got to do as your recommendation. Very great job man !
8) glad it worked. The InputAlert feature is nice but compared to the overall quite sturdy build quality of the device the placement and mechanical sensitivity of the IR led is not too well thought through  |O - especially since it renders the multimeter effectively useless when missing. With a device of that price range I had to investigate further and try to fix it  :)
 


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