No.035 - Locating a PCB short circuit (10 minute)
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- Опубліковано 7 чер 2018
- A 10 minute video showing a technique for locating a dead short on a circuit board using a multimeter.
We've all been there, a short circuit 'somewhere' on our PCB but it could be anywhere. This technique involves no pulling components just to see and no cutting tracks to try and isolate.
PCB = My own PDVS2 design
DMM = Keysight 34461A (6.5 digit)
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There's something so very uniquely satisfying in locating a fault and fixing it.
Excellent Video! Sorry for chiming in, I would love your initial thoughts. Have you tried - Tarbbatigan clean errors Tip (erm, check it on google should be there)? It is a great exclusive product for discovering how to fix electronic devices minus the normal expense. Ive heard some awesome things about it and my friend Sam got cool results with it.
@@rhythmkeebslol
@@rhythmkeebs lol
Glad to see you back online.
Cristal clear explanation, being a great help. Many thanks from over the Channel.
That is a technique I use from time to time too, like you said you need a high resolution on the meter to do it usually.
Thanks for sharing Ian...goes to show that having a low resistance measurement capability extends your troubleshooting set of tools.
Hey up that was a really enjoyable well done that man, this type of subject could carry a whole series, finally wanted to let you the word endoscope popped into my brain when you were explaining the difficulty of looking up at the socket!
Silence brain!!!!
Apologies for the intermittent background noise.......thats my new aircon unit for the workshop. I have to maintain a very stable room temp when calibtrating PDVS2's.
Very nice tip and very well done video. Subscribed.
thank you so much for making this video this has been extremely helpful.
No problem!
Learning curve seems particularly steep on this subject matter. Can anyone point me to a good foundational video series where I can learn to understand PCBs and their various components? Thank you!
Hey, did you manage to find a video series to get started?
@@mazouakh I have not... there's so much content out there but it's so vast it's hard to even wrap my head around. When I learn something it doesn't stick because there's just so much it goes in one ear out the other :/ Every time I start using my meter and get to know it for a project it's 6 months later and have to start all over again. This is not something I will ever pick up just learning bits and pieces over time. Not with my memory anyhow. :)
@@kennethdanteI feel the same way. For some reason there’s a shortage of quality circuitry videos on UA-cam. Almost all of them are flawed in one way or another.
Sailing the same boat...It's hard to know where to start. Head hurts rn from the various videos I've watched 😅
Same here
Thanks. This was great!
Thanks Ian.
Great tip !
Great video very interesting thanks dude
Thanks for the video. It was a bit confusing, as I was looking for a higher reading. I'm guessing because a shortcircuit is shorted to ground that's how you know it was there because there should be no resistance with ground
Brilliant! Thanks.
Very impressive
should do another one of these on another short. Liked it thanks.
Thanks!
Very good demonstration in to electronics. I have a question, is it possible to test a PC123 Optocoupler on a power supply board? Thank you.
Hi Ian! Thank you for all wonderful videos!
Just a side note, add some ESD-protection to the USB-signals. The chips are cheap and REALLY good to have sometimes. Also some protection against reverse polarity (a bit overkill but never under estimate the stupidity of humans).
Will take another look at it at next pcb rev.....but I did read in FTDI AN_146 design guide "FTDI ICs are tested for ESD protection between 2.5KV and 3KV...........sufficient for most embedded applications".
I use a current limited bench PSU and connect it to the meter probes and probe round the fault with the meter, looking for the lowest voltage reading.
Use a air compressor, get the solder nice and flowing and blow the fault chunk of solder or whatever it is out.
How do you locate a short on 3.3 volt line when it is feeding to many different parts of the circuit? I have boards that you can't isolate the circuit.
Let's say a 3 volt supply is feeding to the different parts of the circuit and is now shorted. The PCBA has tons of components. Can I apply this technique?
Hello! I would like to do such measurements, but I cannot afford such an expensive bench meter. At the moment I am trying to decide between an Brymen BM867+ and the Brymen 786 EEV Blog Edition. Both are about 150$. Which one would be better? The 857 has more digits, but the 786 has better accuracy.. Or do you know another mm in that price range which would be suited better? Thanks :)
great video , now I know what the NULL button is for :)
Hey, do you fix boards by chance? I have a handheld tuner device that I believe has shorted.. usb doesn’t turn it on at all, the other connector when it’s plugged into my car, doesn’t turn it on, the cord actually was broken when I plugged it in on accident and it shorted the device. Now it flashed when trying to plug in to the car.
In restoring a cassette deck from 1985, what's the best manner for testing NPN/ PNP transistors in circuit, including DTC-124N digital transistors ?
If you suspected the miniUSB connector, why didn't you just bend up that flappy piece at the back with a spike tool or pointed tweezers. You could get the point in the small gap at the side and lever it up. I'm sure that piece at the back is not essential.
It's a production pcb that once working was always going to be destined for sale to a customer so I didn't want to bend anything. Also, the tolerance around that flap are extremely small, would have been tough to do. The flap is likely for shielding so who knows how essential.
Hi Ian , what if you use Bluetooth interface?
So, I'm a little confused when you measured ohms between the ground pin (I think ground pin?) and the shield of the usb-b mini connector. What resistance should you be reading? Zero ohms I'm guessing correct?
So where was the short?? Suddenly, i see short cleared. Done.
How do you fix the short?
Thx so the lower the resistance number the closer i am to the short correct? I have been dealing with this issue on a board for the last two weeks its killing me!
Correct. You just need a multimeter thats capable of seeing those very small resistance changes. Anything from the BM786 up will do.
What did you do to clear the short? Replace the USB port?
Soldering iron and some flux. Basically, smother the pins and pads in flux and using the heat of the iron you can clear the short. The wetted solder becomes attracted to the pads etc unlike dry solder.
Wish you would have shown that.
You pretty much targeted the location of the short to be at the USB connector, but then how did you finally clear it? The video jumped to C50 "now clear"
Yup, I missed the record button on the camcorder!.........in the end solder wick got me there.
COM95? Nice.
Question that go my eye on: any reason why you haven't use ground planes?
The whole of the underside is one large groundplane, sectioned off for the precision/sensitive areas such as the DAC and LM399AH.
But why not everywhere on both sides?
I'm not saying you did it wrong, I'm just curious if you didn't add ground plane to both sides because of something particular that i didn't know about but makes sense.
Maybe because you wanted to make sure you would not create weak ground connections? And having ground planes would not make you aware of them?
As much as I could the underside has as little traces as possible in order to maximize the plane.....which means a lot of traces topside.....and thus if I added a ground plane topside it would be rather broken and the risk of potential differences (without lots of stitching). There are some ground lines on the topside though, I used rows of grounded vias all interconnected as a guard trace around the sensitive areas. There are advantages either way.....I just chose this way.
Got it, thank you for the explanation
Great vid. Where can i purchase one? Thanks.
On my website, www.ianjohnston.com
Hi Ian. Thanks. I spotted that after posting the comment and just watched Dave’s video on it. Winner winner chicken dinner 👍🏻 what’s the lead times on these? Cheers
Soooo, what was the exact short thing, I mean what was dead? Thanks
I hate USB connectors. Why do the pins have to be recessed? Very hard to rework them.
Recessed pins are partly about shielding, hence why the bent over part almost covers the pins. I guess also about keeping the size of the connector to a minimum.........I agree though, a pain to rework!
Makes sense. Thanks for the info.
My goal is to identify the functions of the devices in a given circuit diagram?
Or spoken more general.
How can I learn this general skill?
When do I see a random circuit diagram in all kinds of electronic fields that I can recognize the devices and their functions?
What is the best strategy to acquire this skill?
Do you know good information recourses specially designated to acquire this skill?
I do not want to handcraft things on my own and I do not want to study at a university to acquire a bachelor's degree in electrotechnology.
I just want to be able to read and being able to understand more or less the circuit diagram.
Thank you in advance
This is a skill you aquire through practise, experience & exposure to the various aspects of electronics & electronic products. Eventually, you learn to recognize groups of components so that when you see a large schematic you can see the grouping and see how they interconnect and thus how the overall design functions.
To acquire it.......well practise & experience will get you there if you put the work in. Studying at Uni, handcrafting etc can all be part of it.
If it becomes a passion......then you'll get there quicker.
lol well that sure does make it easy with a 6.6 digit multimeter
are you fae the North East of Scotland ?
Stonehaven.
I don't quite understand about the short circuit happen more likely around C50 , when C50 has lower ohm and C84 has higher ohm
He had his multimeter on ohm's setting so looking for resistance. So I think it has to do with C84 being further into the motherboard (further away from the issue), there's more components the signal has to travel through therefore greater resistance. I could be wrong, but that's how I interrupted it.
C50 is the easiest accessible (measuring point) and closest to the USB (to where the fault will be discovered later) and as he shows at C50 the reading is around 0.0200 ohms (is the lowest reading so far) and at C85 he measured around 0.0600 ohms (higher reading so is further from the fault).The further you test from the short location the higher the resistance (in milliohms) and as you get closer towards ,,the problem,, the measured value tends to read very, very low (as in close to ZERO in fact dead short) but like he said, you need a meter that has a very good and consistent accuracy in the milliohms range (his is 4 decimals after the dot and that is exactly what it matters the most). And the probes you are using have to be of extremely good quality with pin sharp tips. I myself own a Fluke 289 that has a function allowing me to measure in the milliohms range but it only has 3 decimals after the dot. I never tried such a technic before so I intend to give it a try. It might work as well.
Noob question: via means ground connection? Please confirm. Thank you kindly
Via is a connection between one layer and another. Can be ground or any other signal
I've had Raspberry Pi 3s with shorts on those horrible little USB connectors, hateful things.
What am I missing? The clear the fault just magically happened????? It never said what the problem was!! Comments below seem to indicate that other readers saw what the problem was. What did you do, cut that part out?? I'm so confused.....
how did he clear the short, replace the component ?
No, some flux and slder braid and it was cleared. No need to remove the connector.
So just need blank boards for everything 😂
ESD control I see the PCBA CCA sitting on an insulating cloth and no evidence of ground straps in use
i so hate those connectors without pins sticking out, they dont really save you any space and make life more difficult
Looks to me like poor design of the USB connector. The tab-over is only to retain the insulator assembly, it doesn't need to extend so close to the pins. I see a lot of components designed this way, especially AC fixtures. I know, as long as the circuits aren't touching, all is ok. But why tempt fate? It's easy to bridge a small gap, with solder, or even a small shaving, and there is usually no sense in it. I would look for a better-designed port.
locate short circuit on a PCB
no locating. wellcome to locate
interesting points ,if anyone else needs to find out about
electronics repair jobs
try Saankramer Electronic Magazine System (do a google search ) ? Ive heard some great things about it and my mate got excellent results with it.
Ok had to stop. Suppose to be about locating short circuits and got all the way to middle of video and STILL nothing about tracking down short circuit. BUT it's gets you to watch at least half the video if you last that long. Good for your view time stats. I'm off to learn how to trace short circuits.
This guy is blabla of but don't show how to check for a short circuit.blabla
hard to watch with a light overhead reflecting at the camera