Fluke 87 problem - Page 1
Forum section: electronics / repair

author: Moustafa Eng
author_rank: Newbie
timestamp: November 11, 2017, 11:25:52 am
content: hi guysi have a problem at my fluke,,it shows not correct measurment of ohm and voltage ,aslo when i put my selector on Daiode measurents its shows like shorted with sound.i opend it and test the fuses and found good,also the fusible resistors are fine,,but i found one of MOV is burned ,but it shows OL when i measure betwwen its terminals.i dont know how to troubleshoot it and find where the problem is ,can anyone help attached are photos of the board.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 11, 2017, 05:49:13 pm
content: A number of comments and suggestions.1) This looks like a Fluke 87V, not a 87. It matters because the pcb layout and components are different.2) The fuses, being bad or good, will have no bearing on your ohms and voltage measurement working correctly.3) A burned out MOV is an indication of an "oops" moment where the meter was subjected to very high energy beyond its specifications. A MOV should read 0L with another meter, but if it is black, you should replace it.4) In your picture, the green PTC looks clearly cracked in half (circled in yellow). A good PTC should look like the one in this picture below.https://photos.smugmug.com/Blog-2012/2012-11/Fluke-87-5-Teardown/i-dV9KC7r/0/M/IMG_3928-M.jpghttps://www.eevblog.com/forum/testgear/fluke-87-v-mystery-low-impedance-input/5) A good PTC should measure around 1.1k ohms.6) For testing purposes, remove all 3 blue MOVs and replace the green PTC with a normal 1k ohm resistor. If your ohms and volts measurement work properly, then you can get proper replacements. When testing voltage, don't go above 30V since some the input protection components are removed.7) Any black marks on the pcb might be conductive and affect your readings as well. Clean area with IPA. Seehttp://mrmodemhead.com/blog/ideal-carbon-footprint/

author: ModemHead
author_rank: Frequent Contributor
timestamp: November 11, 2017, 06:31:07 pm
content: In addition to the above, be sure to pop that white switch rotor off and look underneath.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 12, 2017, 12:10:32 am
content: Quote from: ModemHead on November 11, 2017, 06:31:07 pmYeah, like this posthttps://www.eevblog.com/forum/repair/fluke-787-repair-any-idea/msg743281/#msg743281

author: Moustafa Eng
author_rank: Newbie
timestamp: November 12, 2017, 05:50:58 pm
content: guys i really appreiate your help,,,ididnt notice that the ptc was cracked into half...thanks alotmy question is ,,,if i removed all movs and the green ptc ,the avo can work properly or not,,,till i buy the new onealso does the PTC is the one causing the error in measurments till now,,,aslo i have vedios that describ more my case ,,,it doesnt waana upload here ,,can i have your emails to show you it,,it will really help thx again

author: retiredcaps
author_rank: Super Contributor
timestamp: November 12, 2017, 07:18:39 pm
content: Quote from: Moustafa Eng on November 12, 2017, 05:50:58 pmLike I said, if you remove all 3 blue MOVs and replace the cracked green PTC with a normal 1k ohm resistor, test the Fluke 87 on low voltage to see if it works.If it works, then we can suggest proper replacements. If not, then more troubleshooting.