Fluke-107 DMM  Issue/ Repair/ Calibration - Page 1
Forum section: electronics / testgear

author: bhishmar
author_rank: Contributor
timestamp: August 26, 2018, 08:02:43 pm
content: Hi allI have purchased this Fluke DMM (Fluke-107) about 3 years ago for about $60, in India.A few months ago I found that its VDC function (2nd rotary-switch-pos) is not working.It is displaying wild random numbers.Vac readings are also incorrect!Other #4 functions are working correctly [ Ohms, Cap, Amp(dc/ac) ].Because of this the meter is near useless, since Vdc is the main usage.I suspect that, the internal calibration constants for Vdc range somehow got messed up (Dont know how).The offical calibration fee, is I think many times the unit price!Can anybody please help me with the Calibration process, to correct this using some improvised method?Or point to some online resources.There is a calibration window beneath the battery compartment, which accesses 4 gold plated pads in PCB(WP9, WP8, WP7, WP6).

author: retiredcaps
author_rank: Super Contributor
timestamp: August 26, 2018, 09:02:53 pm
content: Quote from: bhishmar on August 26, 2018, 08:02:43 pmBefore you touch any calibration, put the meter into DCV, what reading do you get1) when you short the probes?2) measure an AA 1.5 cell3) measure a 9V batteryHave taken apart the rotary switch to see if there is any debris or dirt that might be affecting the DCV?Finally, post clear focused pictures of your pcb, both sides and we might be able to spot something wrong.

author: bhishmar
author_rank: Contributor
timestamp: August 27, 2018, 01:18:59 pm
content: Hi retiredcapsThanks for ur suggestion & offer for help.I am not a complete newbie in DMMs. But let me try to answer ur queries.I have in my possession following:a) Some Calibrated DC reference standards.(DMMCheckPlus & PentaRef from Doug @ VoltageStandard.com)b) A reasonably calibrated bench Powersupply (0-30V, 5A)c) Some other reasonably accurate (< 0.5% error) DMMS.(AN8002, AN8008 & a UT136).But no high-end equipments.With the help of the above, I tried to test the problematic Fluke-107 DMM.-------------------------------------------------------------Results/Observations:-a) 10A DC & AC Current ranges:-Working very well (Error < 1% & within specs)b) mv AC range:-Not OK .c) V AC range :-NOT OK.The reading is only 24.31% of the applied input AC Voltage,for input= 0.0 to 30V AC, at 1V increments. (But the ratio is same with a variation < 0.2%)But for 240V AC input, was reading 224V !!d) Resistance Ranges:-Outside specs 0.5%. (Now Error upto 1.5%)e) Capacitance ranges:OK within specs ( 2%/ 5%)f)DC V range:-TOTALLY ERRONEOUS & somewhat Random as below.- For probes shorted: reads: -4.xxx random.- For +ve voltages feed from 0 to +6V: Reading varies from -4.xxxV to -1.682V(with no correlation. But Ranging does not seem to work. The range-decimal point is not changing position.Also output reading is not stabilizing)- For -ve voltage feed from 0 to -30V : Reading varies as follows (No correlation):-0 : -4.xxx-4 : -5.76-5 : -13.3-10 : -16.8-15 : -20.74All readings not stable, widely varying (infact drifting in +ve direction)But range decimal point switched one place,at -5: -13.3, above.------------------------------------------------------------------------------Summary:- Current(DC/AC), & Cap ranges working beautifully & stable.- Resistance range somewhat OK (1.5%).-AC V range showing 24.31% of feed input, with a constant ratio (atleast until 30V input) .-DC V range output totally messed up.This fluke DMM I have only used indoors, in my home-lab setup (not outdoor field).So I dont suspect any dirt inside, although NOT 100% sure.Dismantling PCB is OK. But I am hesitant to dismantle the rotary switch. Is it really required?Before dismantling PCB any further tests to be done?Can u make up anything from above observations?rgds

author: retiredcaps
author_rank: Super Contributor
timestamp: August 27, 2018, 09:31:46 pm
content: Using another working meter, what is the input impedance of the 107 when the 107 is set to DCV? That is, put the Aneng meter into resistance mode and measure the input impedance of the 107 when the 107 is turned on and set to DCV.I don't have this 107 model, but I have other Flukes and the input impedance is usually around 11.11Mohm.edit: see my pics athttps://www.eevblog.com/forum/repair/fluke-87-i-repair/msg390462/#msg390462

author: bhishmar
author_rank: Contributor
timestamp: August 28, 2018, 10:07:11 am
content: The measured Input Impedance of VDC & other Voltage ranges of Fluke-107, are given in Table below.3 related parameters are provided as below.a) Product Specificationb) Value measured & documented in Jan 2015,when I purchased it.c) Current (New) measurement value, done today.---------------------------------------------------: DC-V : AC-V : AC-mV---------------------------------------------------a)Specs : >10 MΩ : >10MΩ : >1MΩb)OldValue : 11.1MΩ : -- : --c)NewValue :4.x MΩ!: O.L :32.5MΩ!:13.2MΩ!---------------------------------------------------The VDC input impedance reading4.xMΩ, is not stable.It is varying from3.9x to 4.2xMΩin a minute, & still increasing.But in reverse polarity it is reading13.2MΩ& drifting downwards.Also because of the input series ac-coupling capacitor in AC ranges, the DC input impedance should read infinite (O.L), as is seen in VAC in above table. But the input impedance for the AC-mv range is showing 32.5MΩ!I think I may have to open it up & inspect the series 10MΩ Resistor/s.But the varying (drifting) readings at DC-V indicate some capacitance effect, is'nt it?Any further debugging ideas?

author: retiredcaps
author_rank: Super Contributor
timestamp: August 28, 2018, 07:29:55 pm
content: Quote from: bhishmar on August 28, 2018, 10:07:11 amIt sounds a problem with one of the input protection components. Check the following all in circuit (power off 107 and take out batteries).1) RV1 and RV2 are MOVs. With another meter, RV1 and RV2 should read 0L ohms/resistance.2) RT1 is a PTC. It should be around 1.1k ohm.3) The green resistor above the volt/ohm jack and next to RT1 is a fusible resistor. It should measure around 1k ohm.If RV1 and/or RV2 do not measure 0L ohms, desolder them and verify outside your meter. With RV1 and RV2 removed, try shorting the probes to see if you get 0V and see if a 1.5V AA cell and 9V battery measure okay.Do NOT measure 240V mains ACV without RV1 and RV2 installed.Dave talks about all these components at

author: bhishmar
author_rank: Contributor
timestamp: August 29, 2018, 02:01:09 pm
content: Hi retired capsFinally I went ahead & disassembled my Fluke-107, Removed PCB & also removed the Rotary Swich, to expose the bare PCB. Here are some photos attached.No visible damage to any components, in first look.I measured the resistances of all input side components, using ANENG 8002 DMM.The Green Resistor connected/near V/Ω-Jack (Input Fusible Resistor : R20) = 1.02KΩ.PTC (RT1) = 1.19KΩ @ 29°C.The two blue MOV's (RV2 & RV3: K575) are both Hi-Impedance (O.L i.e > 60MΩ).I also subjected the two MOV's (RV2 & RV3) to higher voltage of 30V from a bench PSU (current limited to 3mA thru a 10K series resistor).They are OK, & are not broken down, & reads 0.0μA (resolution 0.1μA).All measurements are done on dis-assembled PCB, with rotary switch also removed, for maximum protection, & safety of internal circuits.So my conclusion:None of the input protection components have failed.What Next to do ?Since Current (I) ranges (both AC & DC) are working neatly, can we conclude the COB MCU & its ADC are all working perfectly? Or does the chip use different ADC's & input pins for current & voltage measurements?

author: retiredcaps
author_rank: Super Contributor
timestamp: August 29, 2018, 08:06:10 pm
content: The problem is the input impedance is incorrect. Something in the path of the V/ohm jack and COM is causing the 4M ohm reading. Either dirt, debris, a bad or leaky component.Since all the input protection components seem to measure okay, here are some more ideas.1) carefully check the red input jack for V/ohm. Check the soldering, poke and prod the connectors and see if there a snug or loose fit. Use strong light and magnifying glass to check soldering and connection to the pcb. Check for dirt, debris, stray solder material, etc.2) Clean the red input jack for V/ohm using a q-tip dipped generously in IPA.Seehttp://mrmodemhead.com/blog/gallery/fluke-189-clean-up/3) I don't have a schematic and couldn't read one if I did, but see if CR1 is leaky. I'm not sure how to test one for leakage though. I'm asking for this test assuming CR1 is in path of V/ohm jack and COM when 107 is in DCV mode.4) Your pictures don't show the back side of the rotary switch removed (the white plastic wiper). There could be some dirt/debris/damage underneath? Seehttps://www.eevblog.com/forum/testgear/teardown-of-fluke-101-kit/Another reason to completely remove both sides of the switch. Seehttp://mrmodemhead.com/blog/ideal-carbon-footprint/5) Check L2 (inductor) soldering above the COM jack. See if it is making good contact with the pcb on both sides. See if it can be moved if you push it a bit.Seehttps://www.eevblog.com/forum/testgear/bm235-issue-no-loz-dc-voltage-ohms-and-diode/msg1363524/#msg13635246) Sometimes, its not obvious from visual inspection, but any amount of dirt or debris will cause bad readings. Seehttps://www.eevblog.com/forum/repair/fluke-17b-broken-batter-clip-needs-repair/A thorough IPA bath of the entire pcb is recommended as the last resort. I don't think an IPA bath will correct a 7M ohm difference though.

author: bhishmar
author_rank: Contributor
timestamp: August 30, 2018, 06:33:49 am
content: Hi retired capsI have already removed the Rotary switch fully, before doing earlier tests above.However the pictures posted earlier, were taken before removing the rotary switch.Rest assured the PCB & rotary contacts are clean & devoid of any dirt. However there is some sticky colorless substance (grease) in & above the rotary contacts. I suspect lubricating silicon grease.Posting a front side PCB photo + Rotary-contact marking wrto switch positions. I was doing this, in the process of decoding some of the schematic, but not much headway. Mainly because I found the PCB was multi-layered (3 layers). This was quite a surprise for me. None of the teardown reviews here has mentioned this earlier. My PCB version is same as that of the first impression post by 'zapta". (REV 005, TGL3001, 2013).Difficult to trace the middle sandwitched (3rd) layer. Only method is to shine a light at backside, & view the shadow, which is cumbersome, & not always work!Whatever circuit I could gather so far, I am posting here. Btw anyone else in these forums has the full Fluke-107 schematic?CR1 :(SMD 3T dual-diode JY ) BAV199 [85V/150mA], leakage you asked.Incircuit (insitu) Leakage measurement of CR1 diode is near impossible, without risk of damaging other sensitive board components. I dont know!But across voltage measurements are done with DMM-diode mode.Returns 0.632V for left-diode & 0.722V for right-diode. Seems to be OK!But dont know why the two diodes return different values (away by nearly 100mv)Few additional observations:-In both the conditions below, the Impedance measurement btw "V/Ω" & "Com" jacks with another DMM, returned Hi-value /Overload (~ > 60MΩ).Fully assembled unit in power off condition.Fully dis-assembled PCB alone. with Rotary switch also removed.This further corroborates that input-protection components are not the culprit.Since input protection circuit alone will now appear across jacks, since rotary contacts relating to Vdc (for that matter all functions) are disconnected, in this mode.Also Careful Inspection of "V/Ω"-jack does not show anything untoward.L2 inductor soldering inspection OK. Also continuity checks of L2 terminals with jacks & jack soldering points OK.Any further ideas?

author: retiredcaps
author_rank: Super Contributor
timestamp: August 30, 2018, 09:19:59 pm
content: I don't know of any schematics for the 107, but there was/is a leaked Fluke 17B schematic.I suspect the 107 uses an off the shelf chipset that you can readily buy. If yes, studying the 17B schematic might yield clues as to what components to test and measure?I attached a partial screenshot of the 17B schematic.Dave even talked about the 17B schematic in one of his videos. SeeIf you watch or re-watch it again, it might spark some hints/clues as to where to look for this input impedance problem?I might have time to watch it again later tonight, but so far I have a busy 2 or 3 day ahead of me.

author: ModemHead
author_rank: Frequent Contributor
timestamp: August 31, 2018, 12:33:47 am
content: I have no idea what's wrong with your DMM, but I can answer one question and offer a few general things.Quote from: bhishmar on August 29, 2018, 02:01:09 pmMost DMM chips have multiple inputs which are switched inside the chip to the same ADC. There is the main input for AC and DC voltage, which usually follows a 10Meg resistor that forms the upper half of a voltage divider. The chip selects and connects one of several grounded resistors for the bottom half of the divider, according to its auto-ranging algorithm. In addition there will be an "ohms sense" input for the resistance, continuity, and diode test functions that use a current source. Then there's usually another input for the voltage sense from the A/mA shunts.IF the analog functions of the main chip are actually working, then your non-zero readings with open inputs suggests that current is leaking into the front end. If so, then the resulting voltage drop can often be observed with another meter connected in parallel with the faulty one. And if this is the case, attempting to measure the input impedance of the faulty meter will surely indicate a problem, but the actual numbers will be meaningless since the faulty meter is sourcing (or sinking) current. That will confuse the working meter.Sources of current leaks are just about always contamination of some sort, or else it comes from inside the main chip. It's hard for external components in the front end to cause leakage current, because they all lead to analog ground, not to the power supply rails. [Edit:To clarify, leaky front-end components (ie. MOVs, clamps, diodes) can definitely be a problem. It's just that they don't generally cause a voltage drop to appear across the unconnected inputs in VDC mode. Instead they cause problems when the meter itself is sourcing current, ie. resistance, continuity and diode test, or when the meter is connected to an external source.]If you haven't already, I too would recommend submersing the PCB in an IPA bath. Contamination is not always visible. Scrub both sides and in-between components and leads with a brush. Allow to dry at least an hour in front of a fan. If this leads to any improvement, then repeat the procedure.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2018, 03:31:45 am
content: Quote from: ModemHead on August 31, 2018, 12:33:47 amModemhead already knows this, but in the original Fluke handheld multimeter manuals, there was always a theory of operation, bill of materials and schematics that explained the above in written format and then visually in the schematics.The original Fluke 80 service manual even traces the entire path of DCV using bolded lines to show you the operation through the circuit from v/ohm jack right to the main IC.Manuals like this, unfortunately, no longer exist from any manufacturer in any public form. Then I remembered the leaked Fluke 17B schematic which lead me to Dave's video.I can't remember right now, but a good portion of Fluke multimeter fixes here from people asking help does come from a thorough cleaning the entire PCB with IPA and soft toothbrush.If you have several hours to spare, go tohttp://mrmodemhead.com/blog/all-posts/has plenty of examples.Obviously, I can't guarantee results, but all the input protection seems in working order.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2018, 03:39:41 am
content: Quote from: ModemHead on August 31, 2018, 12:33:47 amhttp://mrmodemhead.com/blog/fluke-8060a-repair/"Knowing that leakage current was to blame, it occurred to me that I had never actually cleaned the chip itself. So I dunked it in IPA and scrubbed it with a toothbrush, even though I couldn’t visually spot any contamination. At first it seemed even more flakey, but after several more hours of drying time, it began to work perfectly!"

author: bhishmar
author_rank: Contributor
timestamp: August 31, 2018, 03:37:51 pm
content: Quote from: ModemHead on August 31, 2018, 12:33:47 amYou were right about the above observation.When I assembled back the DMM, & placed in Vdc mode, across its input terminals[V/Ω, COM] it was reading about290mVdc in another DMM. But in other modes like Vac & mVac this was reading ~ 0mV dc. So then it suggest some current leaking into the front-end, in Vdc mode.Overal thanks retiredcaps & Modemhead, for your valuable suggestions & advice.I think I need to subject the PCB to an "IPA bath" as both of you suggested.My IPA stock is near empty, & I have to go and get it from the local shop.So it has to wait a few days.Mean time I need advice from u as to how to go ahead with the IPA bath & scrub?Is it wise to do the IPA bath with the LCD display module attached to PCB?(Since LCD display & its connector can get damaged is'nt it?)I am usually hesitant to remove LCD display from boards, because in my earlier experience (not with fluke), when u assemble it back, 50% of time the uniform pressure on the LCD zebra-elastomeric connector will be messed up leading to missing digits. Once it happens it is quite difficult to get it back correct, by any amount of screw tightening/un-tightening. Do u think this is only an issue with cheap/mediocre equipments, & not an issue with fluke pcb/lcd & designs?@ retiredcaps:Can u please post the full ckt (Fluke-17b) of the partial one u posted.(irrespective of whether it is relevant here), i.e if u have it with u.

author: HKJ
author_rank: Super Contributor
timestamp: August 31, 2018, 04:12:34 pm
content: Quote from: bhishmar on August 31, 2018, 03:37:51 pmI do not believe it is a problem, in my reviews I have torn down more then 60 multimeters, with most of them I removed the LCD display, only one failed to work proper and if I wanted I could probably fix it. The problem was missing guides for the LCD in averycheap meter.I also had one meter where the connection was faulty from the factory, I tried cleaning the board and zebra strip, but that did not help.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2018, 05:17:53 pm
content: Quote from: bhishmar on August 31, 2018, 03:37:51 pmDunk the entire board, but remove lcd. I use a clean soft toothbrush and gently scrub all the components. You may have to repeat 2 or 3 times depending on results and let it dry thoroughly. For me, 1 or 2 times is usually enough.Seehttps://www.eevblog.com/forum/testgear/old-fluke-multimeters/msg633201/#msg633201QuoteRemoving the lcd from Fluke 80s is a common thing. Just be careful in handling procedures. Seehttp://mrmodemhead.com/blog/fluke-8x-faded-lcd/It shouldn't be a problem putting back the lcd given all the teardown videos in the last 3 to 5 years. I don't recall anyone having a problem in the videos.QuoteI didn't post it earlier because it is Fluke proprietary, but since Dave did a video on it, I guess it is okay?

author: ModemHead
author_rank: Frequent Contributor
timestamp: August 31, 2018, 06:33:04 pm
content: Quote from: bhishmar on August 31, 2018, 03:37:51 pmI've probably done it at least 500 times and the only time I can remember serious problems is with old Beckmans, but that's another story.I usually mark the elastomeric connector (zebra strip) so that I can get it back in theexact same positionit was in before. The PCB side of the elastomeric often gets a notched pattern due to the tinned pads, or sometimes PTF (black) pads. It can fail if this side is used on the LCD glass, or gets turned around so the notches don't match up anymore.Do be cautious with fragile plastic bits (clips, guides, etc.) That's generally the number one problem I've encountered, but then again I mostly work on old stuff.

author: bhishmar
author_rank: Contributor
timestamp: September 01, 2018, 07:16:57 am
content: @retdcaps/ @Modemhead/ @HKJThanks for all ur advice & suggestions.If anybody has any Fluke-107/106/101 specific information pls do comment, or share its schematic.I am planning to do the IPA bath & scrub of the bare PCB after removing the LCD panel, as all of you suggested. Incidentally, I have a2.5L "Digital UltraSonic Cleaner". So I am planning to dunk the board fully in IPA within this bath.Currently I am laid up with a severe cold/laryngitis & am not in a position to visit the local shops in the city to re-stock my IPA, for some time.So I have ordered it online now from Amazon-India:NIKS IPA Iso-Propyl AlcoholI hope to receive it in 3-4 days.I will report back my results here later.Meantime if any of you have any extra relevant info, pls feel free to share.Thanks again.

author: retiredcaps
author_rank: Super Contributor
timestamp: September 02, 2018, 12:06:41 am
content: Quote from: bhishmar on September 01, 2018, 07:16:57 amThe ultrasonic cleaner will help too. Seehttps://www.eevblog.com/forum/repair/fluke-189-teardown-repair/Get better soon.

author: bhishmar
author_rank: Contributor
timestamp: September 10, 2018, 06:10:15 pm
content: Hi FolksI did a complete IPA bath & scrub of my Fluke-DMM bare PCB, in myUltraSonic Cleaner.See picture below.But after re-assembling the unit (after blow drying PCB for 5 hours), I find thatthe problem is NOT solved!!The Vdc, Vac, Vac-mv ranges are still completely useless. In the Vdc range of the Fluke-DMM,current/voltage is still leaking into the front-end[V/ohm, Com] Terminalsas suggested by Modemhead before.I am very dejected after spending so much time & effort on this.Now it can be used only for Current measurements (both AC & DC) & Resistance measurement. Which incidentally gives very accurate readings, in fact slightly better than it's specs.I have many DMMS other than this, but mostly these are low cost chinese DMMs (ANENG 8002, 8008, UT136B, UT136C, UT203, UT 602, MetroQ MTQ1090, etc etc ], most of which have dubious input protection circuitry, eventhough many of them are highly accurate. I earlier had an UT-71B (~ 165$), but that got damaged few years back.So thisFluke-107-DMM(even though not high-end) was the one I was depending for MAINS Utility/ Transformer work, or other similar high energy circuits work, with confidence and a relative carefree attitude coming from the associated confidence/safety feeling, for last couple of years.** What I am particularly cross aboutis that, both my higher cost & supposedly reliable DMMs [UT-71B, & Fluke-107 : $170, $60] did not last me 2 years, whereas most of my cheaper chinese DMMS have lasted much more than that !!What an irony?Can somebody complain, if I say Fluke & company.. are much overated & the cheaper chinese ones are very much under-rated, atleast based on my experience above ?

author: retiredcaps
author_rank: Super Contributor
timestamp: September 11, 2018, 03:28:34 am
content: Quote from: bhishmar on September 10, 2018, 06:10:15 pmI'm out of ideas for the Fluke 107 now. Put it aside for now and maybe someday, there will be a leaked schematic or someone else will have the same problem and be able to fix it.If you want to start a new thread on your UT-71B and describe what is wrong, we can try to help you fix it.I have a wide range of meters ranging from $5 and up. However, none of them are new. I buy them broken, used/abused and fix them for learning purposes.Some I cannot fix and while some I can. Maybe future ones that I fix will be related to your 107 problem?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2018, 05:11:04 am
content: Quote from: bhishmar on September 10, 2018, 06:10:15 pmI've tested a fair number of Fluke branded meters and they perform well in every test I have ran compared to many other meters I have looked at. My personal experience is the opposite of what you claim. Obviously, I would have no way of knowing how your 107 was treated. For all I know the other meters you have sit in their boxes while the 107 was connected to the HV supply of an old TV set. I can tell you that I have yet to damage a meter that could be repaired by cleaning it.All of the meters I have looked at were tested on a level playing field, meaning they are all tested the same. I normally run them to failure. I've pushed the Fluke 107 to levels higher than any other meter I have looked at. Obviously, ANY METER can be damaged, including the 107. Here you can see a 20KV transient being applied. You can see how the meter behaves afterward and how I repaired it. There's no magic, drama or bitching about Fluke.If you take the time to look at the spreadsheet where I keep all of the data from my testing, you are going to find Fluke surviving to some very high levels compared to the majority of meters I have looked at. I would be VERY interested in knowing the details about what exactly you did when you damaged the 107. I am always interested in hearing the stories to see if there is some other tests that I could implement.The data for the meters I have tested may be found here:https://docs.google.com/spreadsheets/d/1cXzYpIoyVm9QJUju4KXqM22CEQZP3_xwWvDyeVwxTy4/edit#gid=400910915&range=F4Answers to Frequently Asked Questions may be found here:https://docs.google.com/document/d/1gEPFeOZpsNSm0-7sA98w2P5XE5x77Oal9dQEYvQnF6g/edithttps://youtu.be/X5GrYPBjSDs?t=604

author: bhishmar
author_rank: Contributor
timestamp: September 12, 2018, 04:05:53 pm
content: Quote from: bhishmar on September 10, 2018, 06:10:15 pmQuote from: joeqsmith on September 11, 2018, 05:11:04 amThe last two para of the comments in my post, is neither based on any scientific method of evaluation, nor an objective comparison btw fluke & the cheaper chinese meters. These were subjective comments based on my own experience (that too with a single fluke unit, and some cheap chinese meters).I myself is an engineer & a scientist, who know enough of reliability engineering not to pass any objective judgement or claim on fluke meters, simply based on my limited experience quoted above. I come from an avionics background, so I know that random failures can strike any component or unit any time. No product even of the highest quality & reliability is immune to an occasional random failure.Any product we deem superior is based on the manufacturer following standard quality management practices in the full life-cycle of the product starting from conceptualization, design, realization/ manufacturing-practices & testing-procedures. A brand then make a name based on eventual statistics, while following earlier fundamentals.All the above I know,But that does not prevent me from feelingmadand throw a littlerant, when one fine morning, my supposedly superior fluke unit goes fut on me, with no apparent cause, most probably due to a random failure!(I don't know).So I assure you, my comments & rants were not to be construed in any way against your test findings regarding fluke meters. In fact I have followed some of your surge testing videos, earlier & was quite impressed with them. Thanks to you, it has also helped me sometimes in selecting a relatively robust one from among the cheaper chinese ones.Quote from: joeqsmith on September 11, 2018, 05:11:04 amMy fluke-107, was not damaged while I was testing any mains or high energy circuit, as far as I know. One fine morning I just took it out for a low voltage circuit test, after it was lying idle for few weeks. Then I found it to be faulty as I mentioned in my above posts. That is why I was frustrated & mad. But then I also know a random failure can strike any time anywhere!Quote from: joeqsmith on September 11, 2018, 05:11:04 amI agree. But the cleaning of my fluke-PCB, was done not to repair for any surge failure. It was a suggestion from some experts here, wherein some unexplained problems (mostly contamination related) could be possibly corrected by a thorough PCB cleaning.In fact the input protection circuit of my fluke-107 was quite intact, judged not only by visual inspection, but also by specific & targeted tests on the protection components. But in the absence of any published circuit schematic & due to multi-layer (3-layers) PCB, not much headway could be done to trouble-shoot the fault in detail. So the ultrasonic PCB bath & clean was done as a last resort.

author: bhishmar
author_rank: Contributor
timestamp: September 12, 2018, 04:32:18 pm
content: @retiredcaps, ModemHead, HKJThanks to you for all your suggestions & help, in trying to solve my Fluke-107 problem. Bad luck for me, it did not bear fruit.Quote from: retiredcaps on September 11, 2018, 03:28:34 amThanks for ur offer of help for my UT71B.It is really a re-badged UniT UT-71B. The real name at front is "TENMA 72-7730", which I purchased online from Farnell (element14) in March 2013 (5 years back). It has incidentally a sigrok page:Tenma 72-7730I will start a separate thread on it later."Tenma 72-7730- Issue - Repair - Calibration"Inviting all of you for your help & suggestions there. Thanks again.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 12, 2018, 10:05:55 pm
content: QuoteYou asked and I answered.QuoteI am by no means an expert any anything.QuoteI had read your posts and only saw where you had checked the one diode. I posted the video link showing where I had damaged a different one. It sounds like you have pulled them all from your above comment. These would have been the first thing I would have checked.QuoteFunny, there was another member who had recently posted pretty much the same story. They had used the meter, put it away and when they went to use it, it had a problem. Took a bit to sort that one out.Good luck with the 107. Sorry I could not be of more help.

author: bhishmar
author_rank: Contributor
timestamp: September 13, 2018, 06:12:26 am
content: Quote from: joeqsmith on September 12, 2018, 10:05:55 pmIt is OK. It is only that u misunderstood my above comment to be a very serious one.Quote from: joeqsmithThat is your modesty speaking, Sir. Based on the many Test videos you have posted online, some of which I also have seen, I can surely say you are more of an expert in this field, than many here.Also they suggested the PCB IPA cleaning as a last resort, after I convinced them, that the Fluke-107 input protection circuitry is still intact & not damaged.Quote from: joeqsmithThen u must have missed reading my earlierpost#6above wherein I already confirmed that all the front-end input protection components are intact & not damaged. [Input Fusible Resistor: R20, PTC: RT1, & the two MOV's: RV1 & RV2]Quote from: joeqsmithI did miss checking this one, since I was frustrated & have already finished my troubleshooting, & put away my Fluke-107, by the time ur suggestion appeared in this post. However I will take up ur suggestion & test this when I open the meter again.But then again when I watch your Fluke-107 video, I am confused as to which component do you refer to. CR12,CR13 ? [Time: 15:18 to 15:25, 15:51 -16:05 audio-missing, 17:09]Quote from: joeqsmithExactly. This is why I was mad, when my fluke-107 died just like that.See such behaviours were not uncommon with the cheap chinese meters of 10-20 years back. I have several ones (lost count) which failed like droves, just like this. But the recent chinese ones (last 5-10 years) dont fail just like that, at least statistically. Of course I know their input protection, is either non-existent or at best dubious. Moreover they all falsly claim about their CAT ratings. But other than that they are reasonably good meters (for low voltage circuits). Especially the ANENG 8002 & 8008 meters, which have even passed your tests upto 2.5/2.0 kV transients.But the point is, I never expected my Fluke-107 to fail like that.(I mean found malfunctioning, simply after lying idle for few weeks/months.) I am pretty sure its failure was not due to any Hi-voltage surge/transient related issue, due to a previous usage. I also know you have tested Fluke-107 to 14kV transients & it still survived!So to conclude, I can definitely say the chinese DMMs (including cheaper ones) have improved significantly in the last decade or so (Not in input protection). Regarding Fluke, of course I know I cannot conclude scientifically based on a sample size of "1". (my unit alone)But I have a feeling, that their quality control, on mass production may not be as good as earlier.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 13, 2018, 11:52:27 am
content: Quote from: bhishmar on September 13, 2018, 06:12:26 amI took the time to read the entire thread, which includes your post about the parts you checked. Normally after I damage a meter, I will reverse engineer the front end then start troubleshooting. They are simple enough, I can sketch out the schematic in a few minutes. If you have watched my videos, you may be aware that I have seen parts that will check fine with the another meter but are still defective. There are other parts that make up the protection circuit beyond what you had listed and what was mentioned in the video I linked.All means all!Quote from: bhishmar on September 13, 2018, 06:12:26 amQuote from: Kean on June 01, 2018, 03:51:56 pmSound familiar? If you're interested, you will find the original post here:https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/866/

author: bhishmar
author_rank: Contributor
timestamp: September 13, 2018, 05:20:15 pm
content: Quote from: joeqsmith on September 13, 2018, 11:52:27 amYes, but following are the differences in my DMM-issue, from that of Kean's:-1. After lying idle for few weeks/month, when I took the Fluke-107 DMM to measure a low voltage circuit, it was only an intention, but not carried out. Because the Vdc reading was already reading erratically on switch ON, even without connecting probes anywhere, & even with shorting them. Also the previous instance of using DMM(weeks/month, ago) was sucessfull.2. After the issue, I indeed disassembled it fully (including rotary switch & LCD) & exposed bare PCB (after some initial hesitatiton). There were no visible anamolies anywhere in PCB, including rotary contact pads, with naked eye & some lens magnification.3. Priliminary testing of the front-end input protection components with another DMM confirmed, they are OK.Quote from: joeqsmithI agree.The general thrust of your post/statements seems to indicate, that you still strongly believe that my DMM's problem or damage is due to a power transient, even though my statements are discounting that possibility. This I believe you are putting forth, based on your extensive experience with DMM's, especially fluke.So let me put forth the following additional facts:-I also tried to reverse engineer the front-end circuit, with limited success.When PCB-traces went thru vias to the 3rd (middle) layer, and when I traced them to the top portion of PCB with crowded SMD components, I gave up, because of lack of adequate tools/infrastructure in my home-lab setup.I have posted this partial front-end circuit earlier here in mypost#8above, & reproduced below.I am 100% sure that the main 3 protection components (Fusible resistor, PTC, & MOVs) are un-damaged & OK. These are not only tested by another DMM(AN8002) in resistance-mode, but with some extra rigged up circuitry from a bench PSU setup. Their values were returned correctly by AN8002, & ensured that the MOVs are not punched thru. The MOVs are taking 0.0 uA when 30V was applied to them. I did not want to subject 100's of volts to MOV's in insitu condition.Since the PTC & MOV's are intact, they will protect the downstream elements to some extent. But I know there is still some unprotected path thru R51....One other relevant point, in my problematic Fluke-107, when it is Vdc mode, across terminals there appears a significant DC voltage about 290mV, when measured by another DMM (AN8002).Post #13. This indicates some current/voltage leaking into its front-end from some internal circuits. Can such a failure mode happen with a DMM failed with a power transient, in your opinion?However I am prepared to follow your line of argument. Can u identify the device/devices which needs to be checked, as per your following quote?Quote from: joeqsmithIt is not very clear from your test video, which device you refer to. CR12 CR13 or any other?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 13, 2018, 11:26:45 pm
content: Quote from: bhishmar on September 13, 2018, 05:20:15 pmMy only point with Kean's case is that the story is similar and in Kean's case he had forgotten what he had last exposed the meter to.QuoteI have no bases to believe anything about your meter. I was not there looking over your shoulders. You are the only one who would know how you treated it. Nor would I have any way to know if any of your posts are fact. What I do know is you claimed to have checked every part in the protection circuit and it seems indeed this was not the case. This again is where I would start.QuoteIt's a start.QuoteI have never damaged a MOV with any of my testing. I have lost a few PTCs on the cheap meters. If you damage a MOV you must expose it to far worse than I test to. My tests are all pretty low level. I have seen several cases where the downstream components were damaged without any damage to the PTCs and MOVs. Depends on the design. EVERY Fluke I have damaged, this has been the case.QuoteThere's not much of an argument. I'm just offering the bit of data I saved on the 107. That's been a long time ago. One way would just be to shotgun it. It may be the fastest depending on your skill level. Dumpster may be even faster.