LCR meter question for electronics repair people.

Discussion about old PC hardware.

LCR meter question for electronics repair people.

Postby Ozzuneoj » 2017-11-26 @ 03:30

Basically, I want an LCR meter to more effectively work on old computer parts. The majority of repairs will be on motherboards with electrolytic caps. Being able to tell if they need replaced or not could save a ton of time.

I know nothing about LCR meters though. It seems like I need ones that will support the common capacitance ranges of PC caps, and I guess I should look for something that can test ESR. I don't really know how this works, I just want something that will be useful but not overly expensive, since I'm not doing this "professionally". I have a decent (older) Fluke multimeter for basic stuff, and I own an oscilloscope (which I haven't yet had time to learn how to use), I just need an LCR meter to make testing caps relatively easy.

Anyone have any suggestions? $100 is somewhat expensive to me, but I know that is considered a pittance to electrical engineers and such. I would even buy second hand if it was of high quality if it made it more affordable. As long as it isn't junk and will actually be somewhat useful for testing the usability of capacitors frequently found in PCs (electrolytics, SMD caps and tantalums), it should work for my needs.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-26 @ 04:05

It is a mistake to think you can solve any major problems just with potatoes.
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Re: LCR meter question for electronics repair people.

Postby gdjacobs » 2017-11-26 @ 04:56

As Dave says in the video, that should be a good option for pass/fail testing and rough component identification. When caps go bad, their ESR values tend to explode, so while you wouldn't be able to differentiate between, say, Panny FR and FM series based on readings alone, you could probably tell if the cap has failed or not.

Quality modern LCR meters tend to be pricey, but you can find good prices on eBay for older analog gear. Using a double dial bridge meter should be a rite of passage for everyone.
https://www.ebay.ca/itm/Genrad-1650-LCR ... SwRbtaEj-x
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-26 @ 07:13

Ozzuneoj wrote:Being able to tell if they need replaced or not


I rest my case.

But seriously, once they are out of the motherboard, you might as well replace them with new.
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Re: LCR meter question for electronics repair people.

Postby Jepael » 2017-11-26 @ 10:55

luckybob wrote:But seriously, once they are out of the motherboard, you might as well replace them with new.


Exactly.

As the capacitors will be connected to other components as well, you cannot measure a single capacitor when it is in the system.
For example in CPU VRMs there are many output capacitors in parallel.
If there is a problem in one of them, you don't know which one if you just try to measure them in-system.
So that is why they need to be removed from the motherboard before measuring them individually.
So if the old ones are bad then you need to put new caps in for sure.
If the old ones are good, then half of the job is already done and you can still put new ones in.

But at least you know that if old caps were good and it does not work, then it's something else that is broken.
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Re: LCR meter question for electronics repair people.

Postby BloodyCactus » 2017-11-26 @ 14:51

luckybob wrote:
Ozzuneoj wrote:Being able to tell if they need replaced or not


I rest my case.

But seriously, once they are out of the motherboard, you might as well replace them with new.


and testing then on the board / in system is useless, so remove + replace anyway!
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Re: LCR meter question for electronics repair people.

Postby gdjacobs » 2017-11-26 @ 21:41

It can be useful short of a full recap to pull sample caps and check them.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-26 @ 22:24

just recap the whole damn board. don't do a half assed job by only foing some caps.
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Re: LCR meter question for electronics repair people.

Postby gdjacobs » 2017-11-26 @ 23:03

Le sigh.

Checking sample caps allows you to tell if they've actually failed (as some fall out of spec without any visual evidence). There's no sense in replacing a whole board of perfectly good caps, nor is there sense in not replacing caps that have actually failed just because they look okay.

Furthermore, in terms of reliability just in time maintenance is actually better than preventative maintenance -- it avoids excess early failure. Replacing caps in high heat areas or that have a higher stress function at a higher rate than others is ultimately more reliable than performing a full recap every time.
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Re: LCR meter question for electronics repair people.

Postby dosgamer » 2017-11-26 @ 23:03

Consider getting a real LCR meter like the DER EE DE-5000. Yeah, it's a bit more expensive, around 100 bucks from Japan. But unlike those cheap Chinese DIY projects, a proper LCR meter performs an actual vector impedance measurement at various selectable frequencies, which is important if you want to compare your measurements to the capacitor's datasheet (which is really the only way to accurately tell the health of a capacitor). Also, because it measures both the phase shift and the voltage drop at the same time, it can distinguish between a shorted cap and a good cap (or between an inductor and a capacitor and everything in between). And of course it has a Kelvin connection which allows you to make very accurate low resistance measurements accurate to a milliohm. You can even use it to measure the impedance of a battery.
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Re: LCR meter question for electronics repair people.

Postby Living » 2017-11-26 @ 23:20



i can't stand this guy
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Re: LCR meter question for electronics repair people.

Postby Ozzuneoj » 2017-11-27 @ 00:24

gdjacobs wrote:Le sigh.

Checking sample caps allows you to tell if they've actually failed (as some fall out of spec without any visual evidence). There's no sense in replacing a whole board of perfectly good caps, nor is there sense in not replacing caps that have actually failed just because they look okay.

Furthermore, in terms of reliability just in time maintenance is actually better than preventative maintenance -- it avoids excess early failure. Replacing caps in high heat areas or that have a higher stress function at a higher rate than others is ultimately more reliable than performing a full recap every time.

This is exactly my thinking. If I have a board that "looks" fine and has 10 identical name brand caps on it, I can pull one or two for testing. If its still well within spec, then why recap the entire board? Maybe people who have replaced thousands of caps can do a whole board in a few minutes with little effort, but it takes me a fair amount of time to do something like this and it can often be tedious. Buying hundreds of replacement caps is also not a trivial outlay of money (especially figuring in all the hours involved in using them all before they too are "old").

I'm also interested in testing caps to see how much they truly degrade over time.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-27 @ 01:02

omg you cheap bastards...

If the board is unstable, just recap it from stem to stern AND FUCKING BE DONE WITH IT. I bet you wankers are the kind of people that go to the tire store and buy ONE TIRE AT A TIME and then bitch about how you are at the tire store every other week.

I just recapped a socket 462 board last week. took all of 30 minutes and maybe $10 worth of caps.

Just get the thing I linked to. I just bought one. (With a box, because I'm worth it.) It is perfect for us shade-tree mechanics for a "go/no-go" setup.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-27 @ 01:05

Living wrote:


i can't stand this guy


Meh. When he drags his crotch goblin on for a video I can't stand it. Past that I have no issues. As someone who never "technically" finished his EE degree, he was a great source to fill in the gaps in what I know.
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Re: LCR meter question for electronics repair people.

Postby Ozzuneoj » 2017-11-27 @ 01:23

luckybob wrote:I just recapped a socket 462 board last week. took all of 30 minutes and maybe $10 worth of caps.


Did you replace every single electrolytic cap, even the tiny ones?

If so, congratulations. You obviously have a far greater level of expertise than I in this area, so we're not even close to being on the same page. What may work best for you is not what would work best for me.

When I do electronic repairs it tends to be a surprise when it doesn't take a long time and when it goes without a hitch. :lol:

I'm getting better, but with the volume of boards i have around I simply don't have time to replace the caps on all of them. However, if I get a tester and it turns out that many DO have caps that should be replaced, then I can order large quantities knowing that I will actually need to use them. I'm certainly not going to waste my time replacing a thousand caps on dozens of perfectly stable boards without knowing if they're even close to failing or still well within spec.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-27 @ 01:37

All the electrolytics, yes. All told, 20 caps?

You will get faster, the more you do it. I did my first recap so many years ago. It looked horrible. I'll post the pic later.

Just get a decent iron and a bit of desoldering braid and with practice, it goes quick. I even ENJOY doing it. I like to work with my hands. I put on some Dimmu Borgir and just spend a leisurely afternoon doing 2-3 boards. I just got 5 socket 775 boards that need the treatment, so my next saturday is planned. ^.^
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Re: LCR meter question for electronics repair people.

Postby Ozzuneoj » 2017-11-27 @ 02:21

luckybob wrote:All the electrolytics, yes. All told, 20 caps?

You will get faster, the more you do it. I did my first recap so many years ago. It looked horrible. I'll post the pic later.

Just get a decent iron and a bit of desoldering braid and with practice, it goes quick. I even ENJOY doing it. I like to work with my hands. I put on some Dimmu Borgir and just spend a leisurely afternoon doing 2-3 boards. I just got 5 socket 775 boards that need the treatment, so my next saturday is planned. ^.^


I have a Hakko digital temp controlled iron and a Zhongdi vacuum desoldering station. My problem is that half the time solder still doesn't want to melt, which makes things frustrating. I use the wet sponge and the brass wool and I tin the tip before setting the iron down... and on some boards the solder just never liquefies. Any tips are welcome.
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Re: LCR meter question for electronics repair people.

Postby luckybob » 2017-11-27 @ 02:31

get a roll of the old lead type solder. Flow a bit onto each joint. remove cap, then remove solder via pump or braid.
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Re: LCR meter question for electronics repair people.

Postby Ozzuneoj » 2017-11-27 @ 02:45

luckybob wrote:get a roll of the old lead type solder. Flow a bit onto each joint. remove cap, then remove solder via pump or braid.

I have lead (60\40 I think?) flux-core solder, and I do try to do this, but my technique is probably lacking. Its like the new solder won't stick to the old joint most of the time.

What do you do to prep a solder joint on an old board?
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Re: LCR meter question for electronics repair people.

Postby gdjacobs » 2017-11-27 @ 03:02

luckybob wrote:If the board is unstable, just recap it from stem to stern AND FUCKING BE DONE WITH IT. I bet you wankers are the kind of people that go to the tire store and buy ONE TIRE AT A TIME and then bitch about how you are at the tire store every other week.


Not the sort of maintenance strategy that will fly with anything having expensive downtime or repair cost. Sure, your car tires will tend to wear fairly evenly (unless your front alignment is bad or the weight distribution is uneven). That won't always be the case, and you should never assume so.
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