Short tracing with a millohm meter practical demonstration .
Вставка
- Опубліковано 21 лип 2024
- A couple of weeks ago I showed in a video how I managed to single out a faulty MLCC capacitor from about 20 in parallel in a Samsung TV set and some people complained that I did not show enough detail how its done , so here I present a more detailed video showing how its done , I'm still using one hand to hold the camera but as these are leaded components I can clip on to them using my other hand whilst still holding the camera ! .
- Наука та технологія
The right tool for the job!
Info for those who may not know ...
The 4-wire "Kelvin" connection allows precise measurement irrespective of lead resistance and (within reason) contact resistance to the component on test.
One wire on each clip is to the constant current source, the other to the voltmeter.
A standard multimeter combines them both inside the meter, making them a bit useless for measurement below a few ohms, even when you "null" the leads the reading still depends on connection resistance.
I never used this when I made it as the test leads were about £100 a set , it was only a couple of years ago when I saw the Chinese were making the Kelvin leads at a tenner I started using it !
Nice work, former Rumbelows bench engineer from Wigan
Rumbelows , that's a name I have not heard for a very long time !
Unlike the Ganges river, that was quite clear. Thank you for rectifying that by a good measure. Cheers M.D.
No problem , thanks for watching .
Good practical demonstration, I’ve used the same method too. Would replace all 3 diodes as a preventative measure, if one has failed the others are bound to follow after reassembling the set…
I was thinking the same thing. I notice there's two more empty spaces for diodes too - just wonder if Sharp reduced the count or whether it's relative to screen size as to how many are fitted.
@@MrBetaByte Good point. Makes me want to add two more diodes or replace all three with higher current rated ones. They appear to be paralleling capacitors as well though I can't see the traces to be certain.
@@MrBetaByte Has to do with which model is being manufactured. It's cheaper to make 500,000 of one pcb design and only populate what's needed rather than make (and store) 100,000 of 5 different boards and need spares later, or discontinue one model and have 6,000 leftover that can't be used.
I always replace all 3 , this was just to demonstrating how good a milliohm meter is .
Thank you for your great video and it just shows how much time and effort that can be saved when you use a milli ohm meter
no problem , thanks for watching .
Both this and the original video were quite clear on the topic, but I know how sometimes a second demo on a different circuit can clarify things in a big way. Nice that you can catch a 1 mOhm difference with this meter. My LCR meter (a DER) also can sense down to 1 mOhm, and it's made a world of difference in finding circuit faults quickly. Worth the $. Can easily spot bad caps that show no mechanical failures, too, while in-circuit.
I too thought the first video was perfectly clear but there were a few complaints , my problem with the first video was due to the size of the caps I had to use both hands to hold the test leads and so couldn't move the camera at the same time but on this set I could clip onto the diodes and keep my other hand for the camera .
Well explained Michael 👍
Thanks for that .
This is an absolutely fantastic video. I've known about this from my BTech days but never really appreciated just how useful this could be. I'll definitely be using this method now as having seen this video I can see how many times this would have saved me so much time! Sometimes just seeing a demonstration rather than being taught a theory can really get things to make sense. So love your videos and takes me back to the countless hours I spent as a teenager in TV and Video repair shops.
Agreed, a demo is far better than reading in a book, glad you like the videos when I'm working on vintage stuff it always takes me down a trip on memory lane to my teenage years.
Very clear video - thank you kindly
Thank you for that.
Great video very enjoyable
Many thanks for watching .
Also, removing the faulty diode, cut the legs. When you use the soldering iron, you are only heating the solder on the pad and the tiny bit of leg, rather than the entire diode acting like a heat sink.
Useful advice for anyone just using a standard 25 watt soldering iron, I use a pace soldering station though which goes up to 420 degrees so makes no difference to me .
Only cut one leg to prove the fault, solder it back up if you got it wrong first time.
Sorry, but could you explain this more please? If the diode was faulty and therefore needed to be removed...I would most certainly desolder it and solder in a new replacement. Why would I have to cut the legs? I'm probably reading your comment wrong, but that's just the way it came across. Even if I wanted to check it by desoldering one leg, why would that be worse than cutting the leg? Many thanks
When I've done it in the past, I've just used the bench power supply at low volts and see what gets hot. These days it's so much easier because you've got thermal cameras
Done that in the past and burnt my finger looking , I dont have a thermal camera.
@@michaeldranfield7140 Freeze spray is handy too. The good ones get frosty, the bad ones don't.
Great demo 👍🏻🇬🇧 maybe you could demonstrate how to make a miliohm meter for ourselves .
I made this out of an electronics magazine about 10 years ago so I dont have the schematic , all I can say it was not as complicated as what it may seem .
Watch my channel next week.
Thanks again
No problem .
Recalling the last video's hours of operation observation, I estimated my parent's tube TV use this past weekend -- it has about 109,000 hours (through ~25 years); not a single issue.
Built to fail, in this case , the first thing is basic electronic design, why on earth the manufacture makes this mistake , it can only be deliberate , you cant put diodes in parallel unless you place a current sharing resistor of say 0.1 ohm in series with each diode, 2 ,no RC snubber network across the diodes, the back of the board is marked out to take a resistor and capacitor but there not fitted . 3. the choice of diode fitted only has a PIV of 100 volts and its blocking a PIV of something like 95 volts , the fact that the manufactures has been using this same diode set up for at least 10 years can only mean its done to guarantee failure .
@@michaeldranfield7140 Or to use up excess stock of 100V diodes. Could also have been just to save a few pennies/unit when production started. Operations managers are not engineers but they're the ones who make the production decisions based on parts availability and profits.
@@sincerelyyours7538 cost cutting , they have been using these same diodes in parallel for the last 7 plus years .
I spent 50 years in power supply design and never seen or felt the need to use 3 diodes in parallel. Surely one rated 3 times as much is cheaper that 3.
you would have thought so , but without any current balancing resistor in series or R/C snubber network across the diodes its pretty pointless putting 3 in parallel, there was one set with 5 diodes in parallel !
@@michaeldranfield7140 So would not a diode and a balancing resistor be cheaper than 3 diodes? Maybe it might be a market with diodes with balancing resistors built in the diode? Of course not, otherwise it would have been done. Be interesting to see the detailed cost analysis of 3 diodes vs. 1 diode + 1 resistor -- I wounder if its a close race?
Nice one. Cheers.
No problem , thanks for watching .
I thought the previous video was very clear.
I did but a few people complained it wasn't.
Not confusing to michael, I've been doing this for years, I have to laugh at some of the you tube channels, that mess around changing all 3, they can't own a business.
Not very exciting I must admit but I made this video as some people did not seem to grasp how it was done in my last video
@@michaeldranfield7140 I remember that been in first year training of my apprenticeship in the 70's, the milliohm meter and it's uses, that was an analogue one, kelvins seemed to a strange thing to use back then, but the boss loved test equipment, like you I went on to build my own digital readout milliohm meter, like you said the leads were damn expensive back then, took me age's to save for some second hand one's, plenty of overtime, the boss liked it so much. I was asked to build two more for the workshop, he paid for his own kelvins, I miss those old days .
Hola !!... Dónde puedo comprar el medidor de miliohms que usted utiliza para detectar el componente electrónico dañado. ??
Saludos.
I know this is not built for presicion measurement. but what is the shorted probes offset when connected to a dmm instead of a panel meter?
Sorry I dont know as I have never used this with a digital multimeter .
That fault was on the power supply. The hours used doesn’t account for time it’s off. The power supply is “in use” The whole time it’s plugged in isn’t it? So if the tv is 10 years old but never gets used that’s very different than if this fault happened to a tv that is only a year old. The power supply of the older tv has done quite a lot more work?
This is correct , the psu is still running in low power mode while the TV is is st by but very little current is drawn from the secondary so this does not excuse the diode failure or poor design .
I'm a little disconcerted that the diagnosis relies on 1 part in a 1000 change, on a meter that isn't designed to have super high precision. That seems a bit borderline.
Is there any chance you give the schematic of your milliohmeter ?
I made this out of a magazine about 10 years ago so i wouldn't know where to look now but someone on here is going to see if they can find it who has a better filling system than me !
Watch my channel next week.
Quick question is the milliohms meter powered by ac voltage or battery?
no I made it mains powered so I could leave it on for long periods without a degrading battery affecting measurement accuracy .
132 hours is pretty poor, but I won't knock it as I do make a reasonably good living repairing Vestel tv's. Don't know if it's just me, but more often or not it seems to be the diode in the middle of the three that fails.
I just replace all 3 diodes in one go , this video was just to demonstratt the usefulness of a milliohm meter.
Hello, couldn’t I use my ESR capacitor tester with its digital ohms display? I know this tester uses high frequency to test caps however, I wouldn’t think this would make a difference, your thought anyone?
Only if your ERS meter has a milliohm resolution , the ones I use dont 0.1 ohm is the smallest mine can read
@@michaeldranfield7140 oh thats right, one milli ohm is .001 ohm.
Sir excellent, how can I make this meter, if you can guide please, so regards
Have a look at my other videos , I made one last week with all the building instructions you need to make one .
Nice tip, thanks! Can I ask where you got your milliohm meter kit, or is it your own design?
Sorry not to my design I made this from a design published in an electronics magazine about 10 years ago.
Very interesting way to find a shorted diode, if they were surface mounted, it would save time and hassle.
I would replace all three, if one has failed the other two will at some point.
Underated cheap components are the curse of todays consumer electronics.
"The curse of today's consumer electronics". Yes, the gift that keeps giving and giving :O\
@@ovalwingnut Of course , the gift that keeps giving , this is where you make some money, not spending hours on end just looking at one set , in the 90s it was high value start up resistors going open circuit , now its shorted MLCC s and diodes .
This video was just to demonstrating how a milliohm meter can single out the faulty component rather than removing them all .
@@michaeldranfield7140 As an ex consumer electronics engineer, i was always told that with more than one diode in parallel failing
it is good practice to replace all of them to save a bounced repair.
This demonstration was an excellent way to find the faulty diode.
The quality of todays made to a price sets is not what it used to be.
Hi Michael, like your video, but what i dont get, the diodes are all in parallel, so why is the reading not the same?
because you have the resistance of the copper leadout on the diode and also the resistance copper print that connects all 3 diodes together.
@@michaeldranfield7140 so because you are using a lower resistance to measure (miliohm meter) are you saying the closer you are on each diode (measurement) you are going to get an accurate reading on each component. It's kinda strange to comprehend, as the diodes are all in parallel.
@@audioal8015 Yes this is correct, you can measure the lead resistance of a diode but just the lead will be in micro ohms but when you add this to the resistance of the copper pcb track and the second diode its in parallel with all this can add up to 1 milliohm and this is how you can differentiate between the faulty diode and the good one .
Thanks for the update michael, i dont have a miliohm meter, but I'm going to invest in one. Al.
Hi could you show how to build the meter you made.
Would be great thanks.
Have a look at the comment above this .
Watch my channel next week.
how much,, where to get this milli ohm meter
cost about £30 to make , just check out the magazine I made it from in the video .
you mean the one with least resistance is the faulty one?
correct .
@@michaeldranfield7140 where dud you get the dual tap transformer your homebrew milliohm tester? i want to build one like yours
@@frankbaron1608 Cant remember now but it was either form RS components or Farnell .
2nd request! Do you have a schematic to your Milli-ohm box?
Sorry I dont have the schematic , I made this about 10 years ago from an article I seem to remember was published in Everyday electronics magazine.
@@michaeldranfield7140 - Was that EPE Mag.?
I have all issues back to 1999
@@tubeDude48 Yes thats the magazine .
@@michaeldranfield7140 - Thanks! As I get each issue of the 3 Magazines I get, I keep a plain .txt file with remarks of page number, and title of the Article. I use *Agent Ransack* to search for a particular Article, so it should be a snap to locate the Article on the Milli-ohm meter.
@@tubeDude48 I have them back to the first issue , 1972 I think but I dont have any filling system I just have magazines everywhere in no particular order, not just EE , I also have Television , I use to write for , practical wireless, practical electronics, electronics today international, radio constructor, I literally have thousands of magazines so it wouldnt even be possible for me to look for you , you should also be aware it may not have been called a milliohm meter in the article , it may have appeared under a heading such as short locator .
This is a common fault in this telly
I know its a common fault , the video was not about finding common faults it was about making very small ohms readings.
By far the easiest way of doing this is to use a ToneOhm meter.