FLUKE 189 DC reading problem [with video] - Page 1
Forum section: electronics / testgear

author: kamcm
author_rank: Regular Contributor
timestamp: July 13, 2019, 12:14:35 pm
content: When I use my Fluke 189 to measure 10.000V DC,The measure reading is 8.888V , I feel lucky with this number but I still want to fix itSince it didn't happened all the time, It's really hard to find out the root cause.I checked all the input protection and it seems they are fine.I have clean the gold plated trace under the rotary knob as well but the problem remain the same.Actual input 5VReading 4.8VActual 10VReading 8.888Actual 14VReading 13VActual 19VReading 18.010VActual 20VReading 19.038Actual 21VReading 19.076Actual 22VReading 20.643VActual 28VReading 26.6VWhen I use the 189 to measure 20V, it will display 19.038V andWhen I use the 189 to measure 21V, it will display 19.076V onlyI wonder to know which component will likely cause this 0.04V different on the Fluke 189 meter in that specific voltage range?Please advice,Thanks!

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 13, 2019, 01:54:41 pm
content: When is starting OK you can use it normally if you leave it on ? Maybe a input MOV is dammaged and start to conduct sometimes when voltage is applied .

author: kamcm
author_rank: Regular Contributor
timestamp: July 13, 2019, 03:59:03 pm
content: Quote from: CDaniel on July 13, 2019, 01:54:41 pmI decided to stress test my 189 with my megohmmeter to see if anything go wrongs with input resistance.with 500V, having 10M input resistance, everything looks good.But with 1000V...... it down to 8.38Mohm input resistance only. Somethings obvious not okay.I also tested my 179 and it remain 10M input resistance during 1000V stress test.Which components is failed in my 189?? Is it the MOV or PTC ?How can I found it out without de-solder those components?Please advice,Thanks!

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 13, 2019, 04:09:47 pm
content: The PTC is in series with the input , the MOVs are in parallel , so those could leak some current . I don't think you can be sure without desolder them and see if it measures OK .

author: kamcm
author_rank: Regular Contributor
timestamp: July 13, 2019, 04:29:57 pm
content: Quote from: CDaniel on July 13, 2019, 04:09:47 pmThanks anyway.I just watch this and I think it's more likely the MOV are failed.https://www.youtube.com/watch?v=zUhnGp5vh60&feature=youtu.be&t=1300

author: retiredcaps
author_rank: Super Contributor
timestamp: July 13, 2019, 10:09:01 pm
content: Quote from: kamcm on July 13, 2019, 03:59:03 pmUse your working Fluke 179 to measure the 189 PTC and MOV. You can do this in circuit without desoldering them.The PTC should be around 1k ohm. The MOVs should all read 0L resistance.If the MOVs are not 0L, you can desolder them, for test purposes, and retest the 189 to ensure it works properly. The MOVs will then need to be replaced.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 13, 2019, 10:11:18 pm
content: It seems to me that 1000V tests are a bit close to the rated maximum.

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 14, 2019, 05:53:22 am
content: In this case the failure is not as straightforward for a simple resistance check in circuit ... if you read the first post sometimes behave normal . That's why the conclusive test would be to desolder the MOV and check it outside , or check the meter without the MOV if the readings are correct .

author: kamcm
author_rank: Regular Contributor
timestamp: July 14, 2019, 10:23:25 am
content: I just de-solder all those MOV and check them one by one.I am not sure about the red one (6838)? What's it spec ? Is it also able to sustain more than 500V too?Both blue MOV check with 500V they are goodThe red MOV is fine when testing with 250V, it got OF. But when I test it with 500V, the reading drop down to 0.408M.Please advice,Thanks!

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2019, 11:52:18 am
content: Not sure why you would pull the MOVs but now that they are out, just repeat your low voltage test. From your video, it appears to be a mechanical problem.

author: kamcm
author_rank: Regular Contributor
timestamp: July 14, 2019, 01:12:30 pm
content: Quote from: joeqsmith on July 14, 2019, 11:52:18 amYou're right. Still getting the same problem with MOV removed.Do you have any suggestions? which parts are likely having problems?Thanks!

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2019, 03:54:26 pm
content: From your video, doersn't it appear to be in the switch area to you? I am not sure why you would think this is a component problem. It could be a solder fracture but I wouldn't start reflowing everything like I see some idiots do.

author: kamcm
author_rank: Regular Contributor
timestamp: July 14, 2019, 04:40:52 pm
content: Quote from: joeqsmith on July 14, 2019, 03:54:26 pmIt's because solder fracture will not lead to the input resistance drop down from 10M ohm to 8.38 M ohm (in #3).It's more likely some components leaking current to the GND and causing this happened. That's why I decided to give it a try and de-solder the MOV.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2019, 04:56:13 pm
content: Your video shows it very intermittent. This is not typical of a component failure. Not sure why you would think that a fracture could not cause this symptom. Looking at your video, it seems like the problem is in the switch area.

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 14, 2019, 04:56:36 pm
content: We don't know if the rest of functions work ok , just assuming from the initial post and video that the fault is only on Vdc .Also , when is measuring OK what happens if you touch the switch , turn it just a little bit , apply pressure and so on ... And I asked if you can use it normally when it is ok , measuring different voltages for some time .The big question is , you did something obvious wrong before the issue appeared ?

author: kamcm
author_rank: Regular Contributor
timestamp: July 14, 2019, 06:40:22 pm
content: Quote from: CDaniel on July 14, 2019, 04:56:36 pmThis problem happened on other functions as well.In this video, you will see it jump to the correct value with a long time delay.I think the Knob is not the root cause. I already try to apply extra pressure on the knob to test it.The meter works perfectly before but suddenly this problem appeared.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 14, 2019, 07:30:47 pm
content: have you checked its super capacitor ?? if its rusted or has leaked

author: kamcm
author_rank: Regular Contributor
timestamp: July 15, 2019, 12:31:53 am
content: Quote from: coromonadalix on July 14, 2019, 07:30:47 pmIt's rusted but I don't see a substantial leak.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 15, 2019, 01:16:50 am
content: I dont want to drag your post, but if you dont need time related logs gently remove it to be sure, when this puppy goes bad, you may have excessive battery current draw or an leakage on the pcb, removed mine on my 3 fluke 189 until i bought an substitute.They are known to cause some problems in the fluke 89IV - 189 and 287 or 289

author: windsmurf
author_rank: Frequent Contributor
timestamp: July 15, 2019, 01:37:57 am
content: You might also try Mr.Modemhead's fix (full IPA cleaning of the board).

author: kamcm
author_rank: Regular Contributor
timestamp: July 15, 2019, 09:21:09 am
content: Quote from: coromonadalix on July 15, 2019, 01:16:50 amI just de-solder the battery off the board and clean the spot under the battery.But still having the same problem.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 15, 2019, 10:43:53 am
content: Has windsmurf wrote : do you have any contaminants on the board ?? Any solder residues ?? under the rotary knob functions, is there any grease / too much grease ?Or Maybe your meter need some calibration ??I have my oldest fluke 189 showing a strange behaviour only in ohms measurement under 10k ohms, the ohms ranges seems to works fine, but this one in a 27mhz rf section doesn't show the same values as my other 189 ??, tested all ranges with references resistors, all is ok, all input impedances are fine, but in my rf circuit i have a strange error ?? Maybe its the Fluke asic ic who as a problem ??

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 15, 2019, 01:20:20 pm
content: Should be tested on all functions , maybe if we know what is working right and what is not will figure out the cause .

author: kamcm
author_rank: Regular Contributor
timestamp: July 15, 2019, 02:51:48 pm
content: Here is the test on every functions. Any help would be really appreciated=====================ACACVActual 5VMeasure 4.72VActual 0.3VMeasure 0.0111VAC HZActual 50.00Hz49.96HZ to 50.02 HZ, keep jumping-------------------------------AC mVActual 300mVMeasure 283.94mVAC (mV) HZActual 50.00Hz49.96HZ to 50.02 HZ, keep jumping======================DCActual: 10VMeasure: 8.888V===============DC mVActual: 500mVMeasure: 470.72mV=================ohmactual: 1ohmmeasure: 0.06ohmactual: 5ohmmeasure: 0.19ohmactual: 10ohmmeasure: 0.38ohmactual :20ohmmeasure: 0.79ohmactual: 50ohmmeasure: 37.66 ohmactual : 100ohmmeasure: 88.93ohmactual : 1k ohmmeasure: 0.8893 kohmactual: 5k ohmmeasure: 4.6855 kohm=================mAActual : 20mAMeasure: 19.856mAActual: 10mAMeasure: 10.072mAActual: 5mAMeasure: 5.214mAActual: 4mAMeasure: 4.062mAActual 3mAMeasure: 2.763mAActual 2mAMeasure: 0.076mAActual 1mAMeasure: 0.038mA===================Actual : 100uAMeasure: 101.31uA====================

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 15, 2019, 08:16:44 pm
content: So pretty much everything is bad and in the low side ... the schematic for this meters I don't think it's available but you should try to find and measure the precision voltage reference and power supplies for the analog part , before condemning the ASIC chip itself ...The input protection can't explain the current measurement being off ...

author: joeqsmith
author_rank: Super Contributor
timestamp: July 15, 2019, 09:13:36 pm
content: Quote from: CDaniel on July 15, 2019, 08:16:44 pmAfter seeing the second video, it behaves different from what I first thought. With the data you posted, I concur with the above post in that probing the reference would be the first step. I wasn't able to find a schematic for it but it shouldn't be too difficult to trace this area out. Just takes time. Maybe just have a look around that REF43 under a microscope. Someone had posted some decent pictures here:https://www.eevblog.com/forum/testgear/fluke-187-189-or-87-iv-schematic/

author: kamcm
author_rank: Regular Contributor
timestamp: July 16, 2019, 06:07:26 am
content: Quote from: joeqsmith on July 15, 2019, 09:13:36 pmI had check out the REF43 area and cannot find anything wrong under a microscope.I have also test how much current my Fluke 189 draw from the battery. Here is the result.With the Fluke 189 power off, I still able to measure 55.9M between COM and V socket under 1000V testing.Anyway, I just order some IPA from RS and I am going to clean the board completely with IPA.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2019, 11:04:29 am
content: I doubt cleaning the board will do anything for you. The meter's case looks in very good condition, at least it doesn't appear to have been abused too bad. I would get another meter and start probing that reference. Obviously, you will need a decent meter to do this. Data sheets are on-line for it.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2019, 11:20:05 am
content: For a reference, the attached graph is looking at the current draw of a working Fluke 189 under various conditions. Full disclosure, this data was collected with a home made meter I have been playing around with but I don't see anything strange with yours. If you want more details about this testing, goto the link in my signature. There is a TOC on the first page.Interesting enough, I am playing with this home made source meter now and am using a low cost Brymen BM869s to detect the trends. It has a 500,000 count mode which has worked out fairly well for this.

author: kamcm
author_rank: Regular Contributor
timestamp: August 09, 2019, 09:33:17 am
content: I just cleaned the whole board (both side) with IPABut the problem remain the same.I also noted that when the reading is not correct, if I press the range button to get the reading under manual range, the reading will go crazy out of range.Which components are likely failed ? Is it the resistance network? how can I test it out ?Please advice,Thanks!

author: windsmurf
author_rank: Frequent Contributor
timestamp: August 09, 2019, 07:35:57 pm
content: Just some simple things to check on a used meter if it has measurement issues...Inspect all solder jointsClean Dial contacts - remove old dielectric grease from the dial contacts with IPA and swab, both sides (board and slider)Check the PTC, MOV, and input protection resistorsClean input jack with IPA/swab, check solder for solid electrical connection. The pin under the jack are sometimes broken.Check the resistor network for solid contact (both the board and on the resistor itself). I repaired one that had intermittent connection issues.

author: windsmurf
author_rank: Frequent Contributor
timestamp: August 10, 2019, 08:14:17 am
content: Is your 87V calibrated? I measure current draw of about 3-5mV less on my 189 than what you get on yours.Also, 55MOhms at 1000v I think is normal... I get about 48MOhms on mine at 1000V.I would thoroughly clean your dial contacts on the board as well as the spring contacts under the rotary... and clean the spaces between the dial contact traces. Not just a rinse with IPA but rub well with a QTip. Don't lose those springs as they can pop off and fly away...I might even try swapping the spring contact placements to see if that changes things.Do you get strange reading with no input/nothing connected to the meter when switching modes?

author: kamcm
author_rank: Regular Contributor
timestamp: August 10, 2019, 11:01:38 am
content: Quote from: windsmurf on August 09, 2019, 07:35:57 pmThanks a lot. I have checked all of the components you mention. Everything looks good.I want to check the exact DC voltage go in FLUKE 669918, but I don't know which pin I should probe because no datasheet is available.It would be helpful if someone can tell me the exact pin of DC voltage go in FLUKE 669918.Thanks!

author: CDaniel
author_rank: Frequent Contributor
timestamp: August 10, 2019, 03:31:38 pm
content: So , just to be sure , there is any range for volt , milivolt , ohm , cap , current that is 100% ok ?I have a Fluke 187 with ( as far I can see ) identical board so I could check some voltages .

author: kamcm
author_rank: Regular Contributor
timestamp: August 10, 2019, 04:12:20 pm
content: Quote from: CDaniel on August 10, 2019, 03:31:38 pmAt the time it behave normally, all the function works well and very accuracy.But most of the time. The reading just off the spec.https://www.eevblog.com/forum/testgear/fluke-189-dc-reading-problem-(with-video)/msg2548869/#msg2548869The testing was done with fluke 702. I knew My 702 is accuracy and works well, I verify it with a few meters including 289 and 87V 87III etc.I think the incorrect reading of mA has somethings interesting. In some range the reading just higher than actual.Actual: 10mAMeasure: 10.072mA (Get Higher than actual)Actual: 5mAMeasure: 5.214mA (Get Higher than actual)Actual: 4mAMeasure: 4.062mA (Get Higher than actual)Actual 3mAMeasure: 2.763mA (Get Lower than actual)Actual 2mAMeasure: 0.076mA (Get Lower than actual)Actual 1mAMeasure: 0.038mA (Get Lower than actual)

author: windsmurf
author_rank: Frequent Contributor
timestamp: August 10, 2019, 08:35:26 pm
content: It really doesn't look like its anything in the digital electronics.I still suspect something around the dial, as Joe mentioned, and possibly something in the input.You might try swapping out the PTC to make sure it isn't having strange intermittent issues.... swap out with resistor temporarily if you don't have a spare.

author: CDaniel
author_rank: Frequent Contributor
timestamp: August 11, 2019, 06:52:42 am
content: Current input should be completely independent from V/ohm/cap and has no protection ... so it's not the input PTC , MOV and so on , as I thougth myself initiallyI asked before if the analog voltages are ok , besides the precision reference that ASIC should have dual power supply for the analog internal Op Amps . Inside is the ADC and the True rms converter . Other Fluke multimeters have those as external IC's , much easier to troubleshoot even without the schematic.

author: IconicPCB
author_rank: Super Contributor
timestamp: October 23, 2019, 01:13:53 am
content: In post number nine on the first page of this topic a photo shows some MOVs.I need to identify and source a MOV from the manufacturer of the RED MOV.Please advise the name of the manufacturer if known.

author: BigB_52
author_rank: Newbie
timestamp: April 29, 2020, 02:10:46 am
content: Hi,I have a Fluke 189 which was in storage for a long time with batteries in, when I took it out the battery was corroded, I cleaned the battery cartridge, placed new batteries and turned it on the meter was running for itself without measuring anything, probs were in the air and no matter where the selector switch was. I opened the meter to inspect inside found nothing wrong, no battery liquid leaked and it was supper clean, I changed the supper cap, nothing changed in the result, I sent it for calibration they reported “the meter can not register calibration constants.I tested the eprom 93c56 that holds the calibration constants, it is fine,I can read from and write to it with no problem with an external eprom programmer.Since it came back from calibration facility, the UNCAL mark is on the screen All the time, and the mere shows 0000 in all conditions, even when I activate calibration mode the measurement is zero, the measurement does not follow the input to match the required voltage calibration menu,Any one has any thought in that?ThanksBM

author: EyeDontKnow
author_rank: Contributor
timestamp: September 20, 2024, 02:17:50 am
content: What was the final diagnosis or fix ?I have the same symptoms on my 189......nearly exact readings as the OP.Problem may have started when I "zapped" the leads when measuring +18vdc. But maybe not.*The REF43 test as working.*Pulled MOVs, they tested fine. Without the MOVs (empty) the meter has the same problem as before, no change.*PTC thermistor tested good as well (1k).*PTC and blue MOVs replaced with new, because I had already ordered them.*Red MOV tested fine but not replaced because I have yet to find a replacement part #. (??)*Two resistors adjacent to MOVs test good, in circuit.*String of input resistors (1.5 Meg (x6)) test ok.*Large power resistors near MOVs test good, in circuit.What to do ?I rely on this meter !!

author: EyeDontKnow
author_rank: Contributor
timestamp: September 23, 2024, 04:06:44 am
content: Here is what may have happened before I noticed this 189 faulty readings...I was probing an opamp +18v power pin, the probe slipped, bridging the opamp's OUT and +18vdc pin. Small audible spark. (Black probe was connected to Ground.)This killed the opamp, but was easily replaced. $1Repair for Fluke ? ...... $100+