Fluke-107 DMM Issue/ Repair/ Calibration

[bhishmar]

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 ?

You asked and I answered.

It is OK. It is only that u misunderstood my above comment to be a very serious one.

It was a suggestion from some experts here, wherein some unexplained problems (mostly contamination related) could be possibly corrected by a thorough PCB cleaning.

I am by no means an expert any anything.

That 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.

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.
....
CR1 :(SMD 3T dual-diode JY ) BAV199 [85V/150mA], leakage you asked.

I had read your posts and only saw where you had checked the one diode.

Then u must have missed reading my earlier post#6 above 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]

I posted the video link showing where I had damaged a different one..........   These would have been the first thing I would have checked.

I 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]

My 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!

Funny, 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.

Exactly. 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.

[joeqsmith]

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.
....
CR1 :(SMD 3T dual-diode JY ) BAV199 [85V/150mA], leakage you asked.

I had read your posts and only saw where you had checked the one diode.

Then u must have missed reading my earlier post#6 above 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]

I posted the video link showing where I had damaged a different one..........   These would have been the first thing I would have checked.

I 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.

I 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!   

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]

My 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!

Funny, 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.

Exactly. 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! 

I've been travelling overseas, but now I am back in the lab earlier this week I finally upgraded my 121GW firmware and installed the shim on the selection knob.

Today I went to measure a 12V DC source and the meter displayed 166V.    Then it decided to show OFL, even when measuring a 9V battery!

My initial thought was I had accidentally manually selected a low range, or it was in mV mode, or I stuffed up in alignment of the knob position during reassembly.  But the display matched the various selected range positions.  I took the meter apart and couldn't see any issue... until I removed the range selection switch... and the below image is what I found 

I have not been measuring any mains or other high voltages on the meter.  The only thing that comes to mind is that the 12V I was measuring was at the input to a couple of POL DC/DC converters which was at the end of a long cable, and the DC/DC converters only had ceramic caps.  The DC/DC converter (my own design using TPS54622) is rated at 5.2V 6A out but was struggling to power a Raspberry Pi & pocket 3G router.  Measured with another (Tenma or EEVblog/Brymen) meter I was seeing only about 3.8V instead of the expected 5.2V.

Sound familiar?  If you're interested, you will find the original post here:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/866/

[bhishmar]

Sound familiar?  If you're interested, you will find the original post here:
.....

Yes, 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.

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. ...

I 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 my post#8 above, & 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?

I 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.  These would have been the first thing I would have checked.

It is not very clear from your test video, which device you refer to. CR12 CR13 or any other?

[joeqsmith]

Yes, but following are the differences in my DMM-issue, from that of Kean's:-

My 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. 

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.

I 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.   

I have posted this partial front-end circuit earlier here in my  above, & reproduced below.

It's a start. 

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....

I 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. 

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?

It is not very clear from your test video, which device you refer to. CR12 CR13 or any other?

There'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.