Problems with a Fluke DMM 79 III True RMS: blinking Display in resistance pos. - Page 1
Forum section: electronics / testgear

author: Matse.P
author_rank: Newbie
timestamp: November 17, 2015, 09:23:59 pm
content: Hey guys,I god a brand new problem using my Fluke 79 III TRMS DMM measuring the resistance!When I switched it to low ohms resistance range, everything was ok.But today at 4 pm,, I switched it to high resistance range and as I tested it by shorting out the terminals with the red measuring line I got the following result:The screen blinks and the measurement value is at least negativeWhat's going wrong here? I've never seen such a behaviour before, nut at a Fluke nor any other DMM I own.Please have a look:https://www.youtube.com/watch?v=rcMxsW_HsRE&feature=youtu.beWhat happend? After some hours, the Fluke healed itself and still works fine until now.Is it out of cal so that the measurement of high resistance maybe went down unter 0 Volts in the measurement circuit or what's the deal?I couldn't find any dependencies on moisture or temperature or something like that.Any ideas?Thanx a lot from germany,Matthias

author: retiredcaps
author_rank: Super Contributor
timestamp: November 17, 2015, 09:40:05 pm
content: 1) Look at your video. The low battery indicator is clearly shown. Try putting in a new 9V battery and retest.2) If you had an oops moment, you may have damaged your fusible resistor (symptom #3)http://mrmodemhead.com/blog/fluke-87-fusible-resistor/3) If neither of the above, take apart your meter and post clear focused pictures of both sides of the pcb.

author: Matse.P
author_rank: Newbie
timestamp: November 17, 2015, 10:01:15 pm
content: D'Oh!Used down battery -> I believe a change would solve the problem!I thought the indicator should go from full to empty to show a low battery stage but for this fault a low battery makes sense so that the DMM is no more able to measure the resistance in a right way ...Sorry for my little daffy question ...Thanx a lot for your answer!Greetz,Matthias

author: retiredcaps
author_rank: Super Contributor
timestamp: November 17, 2015, 10:30:53 pm
content: Quote from: Matse.P on November 17, 2015, 10:01:15 pmOnsomemultimeters, there is a status battery indicator that shows you the approximate battery level. But for the 79 III, it definitely indicates low battery as per snippet from manual.http://assets.fluke.com/manuals/7926____iseng0200.pdf

author: retiredcaps
author_rank: Super Contributor
timestamp: November 17, 2015, 10:36:37 pm
content: Here is a picture of the Agilent U1272A. You can see it has a battery level indicator which is showing "full". When it reaches near empty, it will only show one bar and if I remember correctly, when it blinks the batteries need changing now.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 18, 2015, 12:13:47 am
content: One last comment on this subject. Fluke makes a lot of meters that vary with respect to battery life.For example, I put "dead" 9V batteries into a Fluke 75 II and I can probably squeeze out another 200 to 300 hours of use since it only consumes < 300uA (microamps). The Fluke 75 II battery life is 2000 (two thousand) hours using a single 9V battery.One of my favourite meters is the Fluke 187, but the 4 AA cells only last 72 hours. I use rechargeable nimh eneloops so it is not a real problem, but others might find it annoying.The new Agilent U1280A uses 4 AA cells and is rated at 800 hour battery life. The Fluke 28 II uses 3 AA cells and is rated at the same 800 hours.

author: Matse.P
author_rank: Newbie
timestamp: November 18, 2015, 07:38:50 am
content: Thanx a lot for your information! No I see clearly what's going on ...