Fluke 87 V dc amps not working - Page 1
Forum section: electronics / repair

author: DRobillard
author_rank: Newbie
timestamp: May 15, 2020, 04:58:53 pm
content: I have acquired a fluke 87 V which appears to have only one issue. The DC amps (both mA/A and uA) settings do not read correctly. More bizarre is that when I switch to either of these selections the meter reads starting at something like -2.4 and then counts upwards steadily at a rate of approximately 0.1 per second. All other functions work fine as far as I can tell (V DC & AC, ohms, temp, diode, uA mA and A on AC....). I have checked the fuse and the probe is in the correct position.Does anyone have any experience or advice on this?Thanks in advance.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 15, 2020, 05:29:44 pm
content: Service manualhttps://doc.xdevs.com/doc/Fluke/87V/Fluke_87V_Multimeter_Service_Manual-Fluke87servicemanual.pdfThere is some paragraph(s) who explain signals paths ...The usual suspects are any protection device(s) like fuses, diode, or rectifier bridge, mov, ptc, resistor divider network ... unless the meter had a spark or an arc voltage in it

author: DRobillard
author_rank: Newbie
timestamp: May 15, 2020, 06:57:42 pm
content: THANK YOU!The manual plus the few clues you gave me led me to the problem.The manual was telling me that F1 (of course), CR1, CR2, R7, CR5 are there to protect. They appeared fine.Then after a bit more thought, my problem was common to both the A and the mA/uA circuits, so I followed that to R9 (see attached schematic) which measured 30Mohm when it should be 1Mohm. I swapped it out and joy.I got a smoking deal on this meter and it only cost me a resistor and a bit of time.Again Thank you!P.S. Once removed I tested R9 again and it was open circuit.

author: alm
author_rank: Super Contributor
timestamp: May 16, 2020, 05:57:35 am
content: Congrats on finding the issue, and thanks for sharing the fix!

author: Electro Detective
author_rank: Super Contributor
timestamp: May 16, 2020, 07:57:49 am
content: Any thoughts or speculations on what zapped or cooked that resistor ?Something fast and nasty got past the fuseor previous user owner blew a fuse and bridged it out with the wrong type or valueAre the fuses the real deal HRC and correct amperage, and in their correct slots btw?

author: DRobillard
author_rank: Newbie
timestamp: May 16, 2020, 12:26:08 pm
content: Hi Electro Detective.Sorry, no idea what could have happened. The meter was in the scrap pile for at least 7 years and was about to be disposed of when I picked it up. So it came without the case, leads or any accessories but still turned out to be a great deal for me.I have attached a picture with the fuses.I think they are appropriate but I would welcome a second opinion.I also attached a photo of the repair (non-smd resistor). I know,...a little rough... but I didn't want to linger around with any more heat than necessary. The resistor leads are not touching anything else even though it may appear so in the picture. I used some soldering flux and then cleaned it with isopropyl alcohol.Thanks for the interest.

author: DRobillard
author_rank: Newbie
timestamp: May 16, 2020, 12:28:33 pm
content: ...better picture of the fuses....

author: retiredcaps
author_rank: Super Contributor
timestamp: May 16, 2020, 07:33:21 pm
content: The front pcb where the rotary switch is looks like it has some carbon tracks? Seehttp://mrmodemhead.com/blog/fluke-83-iii-rotary-switch/http://mrmodemhead.com/blog/fluke-83-dmm-repair/I suggest cleaning the tracks with IPA.

author: tooki
author_rank: Super Contributor
timestamp: May 16, 2020, 09:02:22 pm
content: Quote from: DRobillard on May 16, 2020, 12:28:33 pmWell, you haven't actually shown any pictures of the unobstructed fuse model numbers. But if they're a DMM-B-44/100 and an FLU 11A, then they're correct.Basically, as long as it's the right size, expressly a multimeter fuse, and one's the 440mA and the other is the 11A, you're good. AFAIK, only a few companies actually make them: Bussmann, Littelfuse, and SIBA.11A: Bussmann DMM-B-11A, Littelfuse FLU 11, SIBA (URZ series) 5019906.11440mA: Bussmann DMM-B-44/100, Littelfuse FLU 44/100A, SIBA (URZ series) 5021006.0.44