Author Topic: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR  (Read 20844 times)

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Online EEVblog

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EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« on: May 28, 2016, 06:11:48 pm »
Dave unboxes, tests, inspects and repairs the first returned faulty EEVBlog BM235 Multimeter.
What will the be the fault?

 

Offline Barny

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #1 on: May 28, 2016, 06:39:45 pm »
Finally the repair-curse is broken.

Excelent video.
Thanks for showing.
« Last Edit: May 28, 2016, 07:42:55 pm by Barny »
 

Offline Wytnucls

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #2 on: May 28, 2016, 07:43:48 pm »
With Dave selling so many around the world, there is little incentive for Brymen to release this meter in their usual market. So this one might become an EEVBlog exclusive. :)
 

Offline alper.y

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #3 on: May 28, 2016, 07:56:39 pm »
Why are there heatshrinks around PTC1 and PTC2 at 10:30? Sorry if it was explained in another video, I have missed it.
 

Offline daqq

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #4 on: May 28, 2016, 08:52:03 pm »
You can get that from stress from some minor board bending. Note the big shunt 'resistor' near to it - this was hand soldered probably into the board and the cooling, thermal expansion etc. could cause long term stress to small SMD ceramic components.

See:

http://www.kemet.com/Lists/TechnicalArticles/Attachments/51/Technical%20Overview%20of%20Flex%20Mitigation%20Solutions.pdf
Believe it or not, pointy haired people do exist!
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Online Dr. Frank

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #5 on: May 28, 2016, 09:37:49 pm »
Solder wetting does not look very well on the other inductor, either.
Reflow temperature may be too low, or components solder contacts have quality issue.

The non broken side of the inductor also came off too easily, so bad solder wetting is very probable.

The case seems to be molded, so correct dry pack handling would be necessary.

If the package was left open too long, the component may have sucked in water, which cracks the case during reflow process.

In either way, high probability of two kinfd of series problem.

Frank
 

Offline bitwelder

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #6 on: May 28, 2016, 09:40:59 pm »
Just curious: if a single SMD component on the tape-and-reel is a little 'wonky', would an average pick & place machine be able to detect the anomaly and discard it?
 

Offline Kleinstein

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #7 on: May 28, 2016, 10:20:14 pm »
Seeing the board, I am not surprised to see that part mechanical broken. Bending of the board gives a lot of stress to that component, as the board is really weak in that range. The connection to the input protection daughter board could give some stress to this area, e.g. when soldering that thick red ground wire, or just vibrations during transport.

So I would consider that one a weak spot in the design. So L3 might fail on other meters as well.

It's just poor placement of the inductor with a slit underneath at an already mechanical weak spot. 
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #8 on: May 28, 2016, 10:36:00 pm »
Solder wetting does not look very well on the other inductor, either.
Reflow temperature may be too low, or components solder contacts have quality issue.

The non broken side of the inductor also came off too easily, so bad solder wetting is very probable.

To me the wetting looks fine because the so called solder meniscus looks exactly like it should be. Here's an example of how the solder meniscus should look, and the one in the Brymen meter looks fine too for Pb-free solder. (attachment, upper joint, lower joint may have been contaminated).



Bad solder wetting looks like this:



Quote
The case seems to be molded, so correct dry pack handling would be necessary.

If the package was left open too long, the component may have sucked in water, which cracks the case during reflow process.

In either way, high probability of two kinfd of series problem.

If that were the case, then the whole series of multimeters that was produced from the same lot of inductors would have shown problems. Assuming this happened, then this might be the first and more will follow eventually. But I doubt it and agree with Dave's asessment that this might be a one off bad inductor.

I have come across SMD components that were knocked off by carelessness. Sometimes the end caps remain in the solder, but often, and despite correct wetting, you're left with just solder. Especially SMD aluminium caps are prone to that. There's a thin intermetallic layer between the solder and the pads and the solder and the component leads. It is this layer that may be responsible for the tearing of an otherwise correct solder joint.
In this particular case, I' assuming that vibrations from transport may have broken the already weak inductor and then shaken loose the other pin as well on this intermetallic layer. Judging by the attachment, the goo from the inductor may have contaminated the solder without affecting wetting.

To me it looks to be a molding error. The goo under the inductor is probably not flux residue from the solder process. I think it's reasonable to assume that the inductor is molded from two part stuff (epoxy?) and that on this one the mixing didn't happen correctly.

Edit: looking at the attachment again, I can't help but think that the left inductor is too small to fit correctly on the pads. The end caps barely meet the pads! I think that according to the IPC610 standards, that's a no no.
« Last Edit: May 28, 2016, 10:53:35 pm by jitter »
 

Offline Kean

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #9 on: May 28, 2016, 10:51:02 pm »
L2 seems to have a crazed pattern on it, so rather than a bad part, I suspect L2 & L3 both suffered a physical impact during assembly.
Dave, if you desolder L2, I wouldn't be surprised if it fell apart.
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #10 on: May 28, 2016, 11:00:04 pm »
L2 seems to have a crazed pattern on it, so rather than a bad part, I suspect L2 & L3 both suffered a physical impact during assembly.
Dave, if you desolder L2, I wouldn't be surprised if it fell apart.

Now that you mention it...yeah, I think you're right. Attachment with a better view on L2, what are those dark streaks?
Would be interesting to see if that residue is also under that inductor... (and how it fits those pads).

« Last Edit: May 28, 2016, 11:05:20 pm by jitter »
 

Offline Kean

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #11 on: May 28, 2016, 11:05:19 pm »
Now that you mention it...yeah, I think you're right. Attachment with a better view on L2, what are those dark streaks?

I'm just looking at L2 on one of my BM235's under a crappy magnifier (I'm working at the home bench, not the office) and it does appear to have some markings or pattern on it.  But in the video it looked like it had a chip out of it.
 

Offline ilanko

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #12 on: May 28, 2016, 11:45:52 pm »
Is that puppy is for sale ?
 

Offline retiredcaps

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #13 on: May 29, 2016, 01:21:57 am »
Related thread on BM235 repair from a different customer ...

http://www.eevblog.com/forum/testgear/bm235-defective/
 

Offline craigh

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #14 on: May 29, 2016, 02:22:56 am »
Hey Dave,

Sorry to hear about your ACL.  I'm a ski guide (take people into the backcountry, not ski fields) as well as an electronics engineer.  I blew my ACL a few years ago skiing.  Since it was a work related injury, I was fast-tracked into surgery. Recovery back to the level that I could ski for work took me a year and loads of physiotherapy (my age - 50+ - didn't help with a speedy recovery).  All good now, five years post-op and my knee works really well (thinking of having the other knee done  :)).

The best advice I got from my fellow ski guides who injured their knees as well (it's a common injury) was to work out as much as you can to improve the strength of the injured leg before surgery.  Makes recovery much quicker.

Cheers mate and good luck,

Craig.
 

Offline gardner

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #15 on: May 29, 2016, 02:40:09 am »
It seems that L2 and L3 bridge an incredibly narrow and flimsy section of the board.  It's narrow to begin with and with the routed gaps underneath is barely there.  With the large HRC fuse clip nearby, this part of the board should be expected to handle a lot of stress/force when the fuse is installed or pulled out.
--- Gardner
 

Online Dr. Frank

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #16 on: May 29, 2016, 02:45:27 am »
Just curious: if a single SMD component on the tape-and-reel is a little 'wonky', would an average pick & place machine be able to detect the anomaly and discard it?

The pick n place machine itself usually does / can not detect t&r or component errors.
It just places the component.
Due to the surface tension of the fluid solder, most placement errors were corrected by self-alignment.

Later, residual errors like this one were detected by AOI.

Frank
 

Online Dr. Frank

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #17 on: May 29, 2016, 03:32:12 am »
Solder wetting does not look very well on the other inductor, either.
Reflow temperature may be too low, or components solder contacts have quality issue.

The non broken side of the inductor also came off too easily, so bad solder wetting is very probable.

To me the wetting looks fine because the so called solder meniscus looks exactly like it should be. Here's an example of how the solder meniscus should look, and the one in the Brymen meter looks fine too for Pb-free solder. (attachment, upper joint, lower joint may have been contaminated).



Bad solder wetting looks like this:



Quote
The case seems to be molded, so correct dry pack handling would be necessary.

If the package was left open too long, the component may have sucked in water, which cracks the case during reflow process.

In either way, high probability of two kinfd of series problem.

If that were the case, then the whole series of multimeters that was produced from the same lot of inductors would have shown problems. Assuming this happened, then this might be the first and more will follow eventually. But I doubt it and agree with Dave's asessment that this might be a one off bad inductor.

I have come across SMD components that were knocked off by carelessness. Sometimes the end caps remain in the solder, but often, and despite correct wetting, you're left with just solder. Especially SMD aluminium caps are prone to that. There's a thin intermetallic layer between the solder and the pads and the solder and the component leads. It is this layer that may be responsible for the tearing of an otherwise correct solder joint.
In this particular case, I' assuming that vibrations from transport may have broken the already weak inductor and then shaken loose the other pin as well on this intermetallic layer. Judging by the attachment, the goo from the inductor may have contaminated the solder without affecting wetting.

To me it looks to be a molding error. The goo under the inductor is probably not flux residue from the solder process. I think it's reasonable to assume that the inductor is molded from two part stuff (epoxy?) and that on this one the mixing didn't happen correctly.

Edit: looking at the attachment again, I can't help but think that the left inductor is too small to fit correctly on the pads. The end caps barely meet the pads! I think that according to the IPC610 standards, that's a no no.

Exactly, the solder meniscus SHOULD look like in your GOOD example, but to me, it does not look like that at all, actually.


The video is not so good, so I tried an enlarged view with contrast improvement, and all the right sides of the components, where the light's shining on, all look really crappy and irregular.
Especially, the right side of the other inductor looks like your BAD case photo.

Maybe, a better photo with good illumination may show different, but here, the solder did not build a meniscus at all.

You cannot ignore, how easily Dave could bend away the inductor on the left side, and if you look closely, you still can see the rectangular imprint of the component inside the solder blob.. so it really hasn't been wetted correctly.. that's the only possible explanation.



And yes indeed, that can really be a series problem @Brymen, with their reflow soldering and maybe with dry pack handling (probably not a component problem)

1/1000 is 1000ppm already, that's much too much, as undetected soldering errors (especially when using AOI) must be in the sub ppm range, nowadays.. believe me, I got a lot of experience from automotive mass production.

Frank

PS: your own photo, showing both inductors side-by-side shows even much better, how bad both are soldered, you can clearly see the lack of the meniscus, and the black spots indicate bad solder junction.. should shine completely.



Here's a more contrasty version.. all junctions look crappy.
Maybe, that area of the PCB was in a thermal shadow, i.e. had seen lower temperatures than other parts.
« Last Edit: May 29, 2016, 04:05:16 am by Dr. Frank »
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #18 on: May 29, 2016, 04:04:14 am »
I'm sorry to disagree. Those solder joints look perfectly acceptable for leadfree solder.
The existence of that shape meniscus means wetting did occur as it should have. If it hadn't, it would not have taken that shape. I agree that the joints look a bit iffy, maybe gritty, but that's normal for certain leadfree alloys.

The inductor was already shaken loose when Dave touched it for the very first time. And as I wrote, the goo on the inductor probably contaminated that joint.

To only mystery left, to me that is, are the black streaks on L2.
« Last Edit: May 29, 2016, 04:10:28 am by jitter »
 

Online Dr. Frank

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #19 on: May 29, 2016, 04:10:20 am »

To only mystery left, to me that is, are the black streaks on L2.

Sign of bad soldering?
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #20 on: May 29, 2016, 04:12:49 am »
Bad soldering shouldn't affect the body of a component. It also doesn't look like overheating. I think I agree with Kean on a mishap. Perhaps something was dropped on the board, maybe someone slipped with a screwdriver.
If it's mechanical stress as a result of the design of the board, I guess we'll be hearing about this problem a lot more in the future.

I hope Dave will remove L2 as well and see if it falls apart and if there's also goo under that one.

Below: the right joint is what I expect to see on the boards we produce using the leadfree solder as SAC is the alloy we use. Looks bad, right? Well, it is a good joint. Lead containing joint on the left, the sight we are (were) used to, but which must not be used as a benchmark when judging SAC alloy joints.
« Last Edit: May 29, 2016, 02:52:16 pm by jitter »
 

Offline station240

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #21 on: May 29, 2016, 06:10:30 am »
Perhaps the crack is the result of the heat during reflow soldering, that is thermal shock.
As the component was broken then it moved before the solder cooled down.
 

Offline imidis

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #22 on: May 29, 2016, 07:14:27 am »
Yeah, he should probably spot check a few to see. Were these meters from the current batch? Definitely will check out mine when it gets here.
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Offline German_EE

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #23 on: May 29, 2016, 07:57:08 am »
Spotted it on the video about two seconds before Dave did, although when I saw the inductor at an angle I thought that it might be making contact at only one end. I reckon that this unit should be auctioned off as a 'special' as it's been worked on by the man himself.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline Flipflop

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #24 on: May 29, 2016, 08:39:42 am »
Mine looks OK, I opened it up this evening and had a quick look. I don't suppose 2 in over 1000 units sold is such a bad failure rate. I wonder if the second failed unit has exactly the same fault?
 

Offline Kean

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #25 on: May 29, 2016, 02:10:54 pm »
Just pulled mine apart again, fully this time, after mentions of the PCB mechanical design in this area due to the large holes, and I can see the PCB flex noticeably around L2 & L3 when inserting/removing F2 (the 11A HRC fuse).  The flex seems more pronounced around the nearby capacitors like C25, but the slots under L2 & L3 definitely create a weak area.

I think an extra moulded support and mounting screw for the PCB near the currrent shunt is required.  Currently there is only one support in this area, and it is closer to the other end of F2.  Another option, which wouldn't change the PCB, only the mould, would be to partly enlarge the mounting post near the COM terminal, so as to provide a support lip for the PCB.  That would only help with downwards pressure on fuse insertion, but on fuse removal the matching half of the moulded case should hold the PCB against the upwards pressure.  This assumes the fuses are installed after the PCB is in the case, which is probably not the case at the factory, so extra care may be required there.

In the meantime, I recommend being very careful when removing or inserting the HRC fuse.  As this is likely to be a common fault, it would be nice to know the factory values of L2 & L3 for replacement purposes, so as to keep up with specs/compliance.  I might remove them from mine for characterisation, or maybe that would be a great topic for an EEVblog video.

Because L2 has been substituted with an 0805 ferrite, I reckon it is more likely to survive fracture from PCB flexing than the 1206 L3.  It does seem that the substitution to 0805 for L2 was an afterthought, and it only just makes it onto one pad of the footprint (see attached photo).  So, on this meter at least, a hairline crack in the soldering of L2 seems much more likely than a broken component.
 
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Online TheSteve

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #26 on: May 29, 2016, 03:40:51 pm »
As I believe has already been stated I think the ferrite was just fine when reflowed but was subjected to flexing or received an impact blow during final assembly.
VE7FM
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #27 on: May 29, 2016, 03:59:36 pm »
Actually, no. Dave's conclusion was a (probably) one off production fault with L3, based on the goo he found under and around that component.

But closer inspection (thanks Kean!) reveals some other issues in that area that may have helped the problem with the inductor to surface. I can imagine if that weak inductor had been in a more rigid area, we would never have known about it. It might have survived for a long time.

For now the more fundamental issues seem to be a weak board around the L2/L3 area, their placement smack in the middle of that area (across slots to make things even worse) and too small size for L2.

Another meter with the same symptoms has surfaced. Hopefully the inspection of that one can shed more light.
« Last Edit: May 29, 2016, 04:07:52 pm by jitter »
 

Offline Fungus

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #28 on: May 29, 2016, 05:45:23 pm »
Am I the only person expecting hoping for a picture of Rick Astley on the inside?

« Last Edit: May 29, 2016, 06:30:45 pm by Fungus »
 

Online coppice

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #29 on: May 29, 2016, 06:12:50 pm »
Why are there heatshrinks around PTC1 and PTC2 at 10:30? Sorry if it was explained in another video, I have missed it.
Thick heat shrink over PTCs and VDRs is a common practice. If you push these parts too hard they can fail explosively and rip right through a case. Restraining them at source greatl reduces the damage they can do.
 

Offline Fungus

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #30 on: May 29, 2016, 06:30:02 pm »
Why are there heatshrinks around PTC1 and PTC2 at 10:30? Sorry if it was explained in another video, I have missed it.
Thick heat shrink over PTCs and VDRs is a common practice. If you push these parts too hard they can fail explosively and rip right through a case. Restraining them at source greatl reduces the damage they can do.

They also make a mess.

Quite a few PTC were turned to dust in the meter robustness testing thread. The heat shrink helps keep all the dust in one place.

 

Online EEVblog

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #31 on: May 29, 2016, 07:56:55 pm »
With Dave selling so many around the world, there is little incentive for Brymen to release this meter in their usual market. So this one might become an EEVBlog exclusive. :)

It might by default.

I was surprised at the small number of their initial batch.
 

Offline Dr.Joe

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #32 on: May 30, 2016, 12:43:20 am »
Mine looks OK, I opened it up this evening and had a quick look. I don't suppose 2 in over 1000 units sold is such a bad failure rate. I wonder if the second failed unit has exactly the same fault?

As i am the owner of the second faulty unit: yes it did. Just not as bad as the one Dave repaired. My inductor was still intact, just lifted from the lower pad (by about 0.25mm). I did resolder the joint, and the Meter is working again.

I didn't even have to desolder the Input Board.
 

Offline retiredcaps

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #33 on: May 30, 2016, 01:23:00 am »
As i am the owner of the second faulty unit: yes it did. Just not as bad as the one Dave repaired. My inductor was still intact, just lifted from the lower pad (by about 0.25mm).
@Dr. Joe

I wonder if yours is in the same serial number range as the one in Dave's video.  If yes, there may be some other owners who will want to look at their unit especially if you don't have to desolder the input board.
 

Offline Dr.Joe

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #34 on: May 30, 2016, 02:11:44 am »
I can't remember Dave showing the serial number of the one he repaired, but mine is 161140685
 

Offline Kleinstein

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #35 on: May 30, 2016, 02:17:09 am »
As the root cause seems to be the board layout with large form factor SMT parts soldered over a position with high mechanical load (or more accurate strain), the problem will not be limited to a few units. I am afraid all units with this board layout problem have a weak spot there.

I would consider this a point that should be addressed at the next board revision. It might be even a reason to start a new board version.

Some may fail early if the soldering is not the very best quality - failing solder may be the better case as resoldering can make it work again. With good solder joints the inductor itself can break - just like in the unit Dave showed.
 
 

Offline QuantumLogic

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #36 on: May 30, 2016, 03:08:40 am »
I can't remember Dave showing the serial number of the one he repaired, but mine is 161140685
The one Dave repaired was 161140533.
 

Offline Flipflop

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #37 on: May 30, 2016, 03:43:23 am »
The photo that Kean posted shows that those 2 inductors are almost the only thing holding the board together at that point.

I wonder if the BM257 and BM257s are the same in this area?
 

Offline Lightages

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #38 on: May 30, 2016, 04:26:19 am »
The photo that Kean posted shows that those 2 inductors are almost the only thing holding the board together at that point.

I wonder if the BM257 and BM257s are the same in this area?

The BM257(s) does not have components in the same place on the circuit board. I suspect that there won't be any kind of failure in the same way if it does turn out to be a mechanical stress problem on the components in the BM235.
 
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Offline blacksheeplogic

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #39 on: May 30, 2016, 06:43:10 am »
It's good to see the honesty with a possible issue in these.

Also, to address a point on one of the threads regarding failure of the mid-tier brand verse a traditional top shelf (Fluke for example). I have had to returned two Fluke meters out of the box. A Fluke 28II  and a Fluke 1507. The Fluke 28II was replaced, and the Fluke 1507 was serviced and returned to me. I can accept that the Fluke 28II failed after factory calibration/shipping, but the Fluke 1507 should not have passed QA as it was a fault with the molding.

 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #40 on: May 30, 2016, 07:18:41 am »
As the root cause seems to be the board layout with large form factor SMT parts soldered over a position with high mechanical load (or more accurate strain), the problem will not be limited to a few units. I am afraid all units with this board layout problem have a weak spot there.

Agreed. When looking at the photo Kean took of a board outside the case, I couldn't help but think "what were they thinking". And they did it knowing full well that it might not be that strong, they tried to counter it a bit by not having the slots under L2 and L3 sit in line with eachother, but they are offset.

Quote
I would consider this a point that should be addressed at the next board revision. It might be even a reason to start a new board version.

Indeed, especially if dropping the meter, or inserting a fuse leads to problems in that area.

Quote
Some may fail early if the soldering is not the very best quality - failing solder may be the better case as resoldering can make it work again. With good solder joints the inductor itself can break - just like in the unit Dave showed.

I think now that maybe Dave's conclusions on the inductor were wrong. He speaks of black goo under the inductor, and indeed when you look at the remains of the inductor at first it looks like black goo. But if you look closer you can see the light shine through a piece of it sticking out from the underside of the inductor (first attachment, it's clear not black). There's also quite clearly residue on the good end cap of the inductor, which I previously called contamination

I think I should stand corrected on my remarks that these are good solder joints. They are still good in the sense that there has formed a meniscus, and the slightly gritty nature of the joint is inherent to some alloys of leadfree solder. But there's also some yellowish residue covering the joint that you can see at 15:35 when Dave scrapes it off the joint with his pointer (second attachment).
I have seen this residue form on the boards we produce as well, but they should not form in such a thick layer under that inductor, but rather puddle around the pads like you can see at 12:28 around the unpopulated transistor pads.

I don't think the solder profile was wrong, but perhaps the solder paste was past its use by date, or something like that. And in the weakest area of the board this will be the first where it will lead to problems. So perhaps the inductor was fine when it came from the tape after all, but it was damaged by strain later on.
« Last Edit: May 30, 2016, 03:57:58 pm by jitter »
 

Online coppice

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #41 on: May 30, 2016, 10:43:24 am »
Why are there heatshrinks around PTC1 and PTC2 at 10:30? Sorry if it was explained in another video, I have missed it.
Thick heat shrink over PTCs and VDRs is a common practice. If you push these parts too hard they can fail explosively and rip right through a case. Restraining them at source greatl reduces the damage they can do.

They also make a mess.

Quite a few PTC were turned to dust in the meter robustness testing thread. The heat shrink helps keep all the dust in one place.
When the option is sharp objects punching through even tough polycarbonate cases, possibly taking an eye out, its legal liability which drives those heat shrink sleeves. Who cares if the shards are neatly gathered?
 

Offline Fungus

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #42 on: May 30, 2016, 07:17:35 pm »
Another option, which wouldn't change the PCB, only the mould

They have mould inside them? Interesting.

What it for? Does it absorb the inevitable crumbs of food that fall inside when you're connecting/disconnecting the leads?
 
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Offline Len

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #43 on: May 31, 2016, 01:12:44 am »
Another option, which wouldn't change the PCB, only the mould

They have mould inside them? Interesting.

What it for? Does it absorb the inevitable crumbs of food that fall inside when you're connecting/disconnecting the leads?

Don't get too excited. He wasn't talking about fungus, Fungus.
 
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Offline Kleinstein

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #44 on: May 31, 2016, 01:50:58 am »
There may be a good reason to start with relatively small batches - so there might be the option to get an more robust version in the future. The slots below the inductors make things mechanically worse, not better. Still wondering of these slots are really needed, as the inductors are more like for ESD purpose.

I would guess a board revision might be less trouble than changing the mold for the case. Some changes may be possible, but some are very expensive.
 

Offline Flipflop

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #45 on: May 31, 2016, 04:10:29 am »
Still wondering of these slots are really needed, as the inductors are more like for ESD purpose.


I was thinking this also as the input/blast protect (apart from fuses) seems to be on the little board with the input jacks.

I'm a little surprised that Dave didn't pick up on this 'weakness' with this meter as he is usually very thorough doing his meter teardowns.

I was also surprised to see that the current jacks are split in 2 halves to act as switches for the 'beepjacks' feature as in some of the previous meter videos Dave frowned upon jack sockets with splits.
« Last Edit: May 31, 2016, 04:56:02 am by Flipflop »
 

Offline rch

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #46 on: May 31, 2016, 08:23:34 am »
Another option, which wouldn't change the PCB, only the mould

They have mould inside them? Interesting.

What it for? Does it absorb the inevitable crumbs of food that fall inside when you're connecting/disconnecting the leads?

'Mould' is the correct UK (?Australian) spelling.   'Mold' is a town in Wales, FWIW.
 
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Online EEVblog

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #47 on: June 01, 2016, 09:15:22 pm »
Brymen have investigated it, report attached.
 
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Offline Kean

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #48 on: June 01, 2016, 09:25:13 pm »
Brymen have investigated it, report attached.

So they're basically saying it was likely damaged during assembly then, most likely during fuse insertion?  I agree.

I was flexing the main PCB with the terminal PCB disconnected, and I see that the red wire would provide support as it is quite stiff.  But if the fuse is inserted before adding the terminal PCB and gaining that extra strength, then I can easily see this happening to 2 in 1000 units.

An excellent response by Brymen in my opinion.  :-+
« Last Edit: June 01, 2016, 10:16:40 pm by Kean »
 

Offline rrinker

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #49 on: June 01, 2016, 10:08:18 pm »
 :-+

Clearly they are on top of things. I am very impressed with the quality feel of mine, and it's good to see the company has solid procedures in place to handle and correct small issues that may crop up.

 

Offline GEuser

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #50 on: June 01, 2016, 11:18:39 pm »
That's a good thing there .
Soon
 

Offline iromero

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #51 on: June 02, 2016, 01:32:29 am »
Brymen have investigated it, report attached.

That report is awesome, exactly what you would expect from a manufacturer with a quality system in place. Gives even more confidence on the brand.
« Last Edit: June 02, 2016, 01:34:43 am by iromero »
 

Online Vgkid

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #52 on: June 02, 2016, 02:43:19 am »
Nice job by Brymen.
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Offline bitwelder

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #53 on: June 02, 2016, 03:40:56 am »
Good job Brymen also in allowing to share the report (I guess Dave got permission to publish).

Can somebody re-explain in simple English what does it mean that "L3 was soldered to left trend"?
 

Offline Wytnucls

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #54 on: June 02, 2016, 04:03:02 am »
I think Brymen means to say that if the L3 solder is intruding slightly in the left post circular opening, the solder joint could get damaged during meter assembly or disassembly.
« Last Edit: June 02, 2016, 04:05:09 am by Wytnucls »
 

Offline jitter

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #55 on: June 02, 2016, 04:41:19 am »
I think Brymen means to say that if the L3 solder is intruding slightly in the left post circular opening, the solder joint could get damaged during meter assembly or disassembly.

That's indeed what they're saying. They are also proposing a check for existing finished stock and a workaround for work in progress and a permanent fix for the long term.
However, looking back at Dave's video, it is clearly visible that the inductor is perfectly placed on the pads without any shift to the left or the right. It's mainly a design issue that the long term fix should solve.

What they did not go into were the other things remarked here:
- a lot of residue under L3/solder quality;
- weakness of the board in that area;
- undersized L2.
« Last Edit: June 02, 2016, 04:55:15 am by jitter »
 

Offline Flipflop

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #56 on: June 02, 2016, 04:50:38 am »
I'll give Dave and Brymen full marks for being open and honest about this. At least it has been recognised and addressed as a design/assembly problem.
 

Offline retiredcaps

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #57 on: June 02, 2016, 07:43:28 am »
Thick heat shrink over PTCs and VDRs is a common practice. If you push these parts too hard they can fail explosively and rip right through a case. Restraining them at source greatl reduces the damage they can do.
Speaking of the above.  See pics of PTC in heatshrink at

http://www.eevblog.com/forum/repair/brymen-bm869-meets-high-voltage-in-real-world/
 

Offline jesuscf

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #58 on: June 05, 2016, 01:45:45 am »
I good job will include the part numbers for both L2 and L3.

Good job Brymen also in allowing to share the report (I guess Dave got permission to publish).
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Offline jancumps

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #59 on: June 05, 2016, 01:52:41 am »
I good job will include the part numbers for both L2 and L3.

Good job Brymen also in allowing to share the report (I guess Dave got permission to publish).

Why? That doesn't add or take away from the report.
 

Offline ornea

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #60 on: June 06, 2016, 09:17:50 pm »
Was just going thru the manual.  Looking at the hires teardown photos included it appears L2 has a crack.  Can't be 100% sure.
 

Offline ornea

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #61 on: June 06, 2016, 09:41:53 pm »
I good job will include the part numbers for both L2 and L3.

Good job Brymen also in allowing to share the report (I guess Dave got permission to publish).

Why? That doesn't add or take away from the report.
True. But it does make it easier for people wanting to do their own repair if required.
« Last Edit: June 07, 2016, 01:58:59 am by ornea »
 

Offline ornea

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #62 on: June 06, 2016, 11:56:44 pm »
Brymen have investigated it, report attached.

That report is awesome, exactly what you would expect from a manufacturer with a quality system in place. Gives even more confidence on the brand.
Adequate report would be my take on it.
 

Offline Flipflop

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #63 on: June 07, 2016, 04:03:33 am »
Was just going thru the manual.  Looking at the hires teardown photos included it appears L2 has a crack.  Can't be 100% sure.

If you zoom in there is something there on L2, not sure if it's a crack or just some mark.
 

Offline imidis

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #64 on: June 08, 2016, 05:09:20 am »
Received mine today, seems to work quite well, haven't taken it apart to have a look at l2 l3 yet.

For anyone else from Canada, got charged PST, GST, and 9.95 to determine there was taxes and no duty on it, $25 cad total for that.
Gone for good
 

Offline timofonic

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #65 on: June 08, 2016, 08:48:00 am »
Can this model be distributed in Europe?
 

Offline drussell

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #66 on: June 08, 2016, 10:57:52 am »
Received mine today, seems to work quite well, haven't taken it apart to have a look at l2 l3 yet.

For anyone else from Canada, got charged PST, GST, and 9.95 to determine there was taxes and no duty on it, $25 cad total for that.

That sounds about right....

For Canada Post, they charge a minimum of $5 for the "fee to clear it through customs" if it is more than a few dollars value of actual product (if it is less than some small minimum value of about $20, they usually just let it through un-charged) and then that base fee goes up depending on the actual declared value of the item. 

Add the 5% GST (and for any province other than here in Alberta, add your tragic PST %) and you've got your import charge...

(Although sadly, of course, with our atrocious new NDP government here, we'll probably have a #*?&@%$FrickyFracken#*$%@&?*#! provincial sales tax here too soon enough...  :palm:  but I digress...)
 

Online EEVblog

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #67 on: June 08, 2016, 01:20:32 pm »
Was just going thru the manual.  Looking at the hires teardown photos included it appears L2 has a crack.  Can't be 100% sure.

Nope, just some marks.
 

Offline imidis

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #68 on: June 08, 2016, 09:08:29 pm »

That sounds about right....

For Canada Post, they charge a minimum of $5 for the "fee to clear it through customs" if it is more than a few dollars value of actual product (if it is less than some small minimum value of about $20, they usually just let it through un-charged) and then that base fee goes up depending on the actual declared value of the item. 

Add the 5% GST (and for any province other than here in Alberta, add your tragic PST %) and you've got your import charge...

(Although sadly, of course, with our atrocious new NDP government here, we'll probably have a #*?&@%$FrickyFracken#*$%@&?*#! provincial sales tax here too soon enough...  :palm:  but I digress...)

We all will have HST in the end one day  :palm:

Yeah, 7%, so that was 8 and some change, on the plus side, they undervalued it slightly, exchange maybe?


On another note, I did take it apart and check out L3, L2 on mine, looks good.   :)
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Offline hugatry

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Re: EEVblog #884 - EEVBlog BM235 Multimeter REPAIR
« Reply #69 on: November 19, 2018, 02:01:14 am »
Here is a picture of newer board revision. L3 has been repositioned so that it won't end up sandwitched between PCB and plastic post on the rear half of the case.
This kind of fix was mentioned in the report shared by Dave, but here is an actual photo... Just so everyone knows this problem got fixed sometime during last two years.

This is actually Brymen BM231, but AFAIK PCBs are the same for all models in BM230 series.


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