Fluke 175 and 179 side-by-side / Backlight hack on Fluke 175 - Page 1
Forum section: electronics / testgear

author: CosPhi
author_rank: Regular Contributor
timestamp: April 30, 2014, 08:38:39 pm
content: HelloI bought a Fluke 175 multimeter for me just as an second meter. Already before I bought it, I was wondering, if it is possible to add an backlight on the Multimeter.So I took the 175 to work, where we have 179's for everyday use (I'm an industrial electrician). I opened both and made some pictures side by side. On the left side on the pictures is the 179, on the right side is my new 175. The 179 is I think around 10 years old but still works well. Anyway I think the Fluke 179 is hard to beat as an everyday multimeter for everybody on work.So back to the backlight ... I did read somewhere her in the forum "it does beep" if you push the backlight button on the 175 pcb. But there was not more, just it "might" work.And yes it not just beeps ... it also does "turn on" the backlight ... just all the resistors, the transistor, the led's are missing on the 175 pcb (and of course the button itself). But the controller does switch +3,3V. So when you add all the part's the backlight does work and shineThere is also the prism missing on the 175 display, so it might be better to put the led direct into the display instead of on the pcb. I'm also not sure now how is the best an most "beautiful" way to add the button. The best and way would probably be to use an 177/179 button pad. Then the only thing you would have to do is to drill an hole into the housing.Any ideas or inspiration?martin

author: retiredcaps
author_rank: Super Contributor
timestamp: May 01, 2014, 06:01:13 am
content: Quote from: CosPhi on April 30, 2014, 08:38:39 pmYes, it can and has been done. Modemhead made the modifications, but he is away for the foreseeable future right now. I will let him know about this thread once he is back. He has all the details. See picture in this thread below.https://www.eevblog.com/forum/testgear/fluke-175/

author: smoothtalker
author_rank: Regular Contributor
timestamp: May 01, 2014, 07:34:16 am
content: wow the pcb looks interesting. the 179 actually missing a thick-film resistor network as compared to the 175, just beside the big limiting resistor. I am not a EE so i could be wrong! but it's interesting.

author: CosPhi
author_rank: Regular Contributor
timestamp: May 01, 2014, 11:26:09 am
content: Quote from: smoothtalker on May 01, 2014, 07:34:16 amI guess the new 179 have also just this thick-film resistor. The 179 on the picture is pretty old. I'm more wondering about was is missing under the COM jack (most bottom, right side). There are also some parts missing on my 175. I don't know if that's for the temp probe or something?Quote from: retiredcaps on May 01, 2014, 06:01:13 amI didn't saw that when I searchedBut it can done .. I already know. I just search a good way for the button and the prism/diffuser. He wrote like he did just took the parts from the 177. Maybe I also should desoldering all parts on my company's 179The buttons I saw now on ebay. For the led, I guess I like another color instead of green. I very like the orange on my Agilent U1272A.

author: sambonator
author_rank: Regular Contributor
timestamp: February 25, 2019, 04:48:22 am
content: Old thread... but has anyone been able to figure out the value of resistors and type of transistor used?Thank you!Sam

author: ModemHead
author_rank: Frequent Contributor
timestamp: February 27, 2019, 06:21:54 pm
content: Quote from: sambonator on February 25, 2019, 04:48:22 amThis is a photo of a 177 with Rev 015 PCB. The backlight transistor is marked "1R" which I think is a MMBT5809 general-purpose NPN transistor. Given the application, I would expect any GP NPN transistor that can handle the LED current would work. The original LED current-limiting resistor is 475 ohms for about 10mA max. I would change this based on what your desired LED current is. The base resistor here is unmarked, but it measures 50K.

author: sambonator
author_rank: Regular Contributor
timestamp: February 27, 2019, 06:36:29 pm
content: Thank you so much Mr.ModemHead! Now to scrounge for parts....BTW I have bedhead today.