I was just searching to see how to put a multimeter to millivolts and seen this video. I finally see how diode measured to find if they aren’t working. Video is beyond excellent.
I have a digital ESR meter but I never know I could used it in other way just like what you did in this video. Thanks for sparing some time to share us your skills sir.
What a fantastic video! Over my self-educated time spent (100's and 100's of videos and some books), what no one ever said/wrote was that in repairing electronics, it all comes down to OPENs and SHORTs; with SHORTS being the "variable" cause ... meaning that there can be a SHORT ...or... a PARTIAL SHORT that's causing the problem. Once that became apparent, troubleshooting changed to "much easier" to diagnose. I have a Zapper, built a LeakSeeker, have injected voltage, and and and. This video from 7yrs ago ... I wished I had discovered earlier. It added a very valuable approach ... inject a small voltage and then look for a voltage drop in the mA's (or maybe even uA's if you can). Brilliant. Thanks for this video.
Thank you for the comment. It's always nice to hear when someone appreciates on of my videos. We had a period where bad capacitors kept repairmen fairly busy due to a manufacture error known as the "capacitor plague", but that's not so common anymore, so other than bad eeproms and leaky parts, I suppose shorts and opens do make up the bulk of repairs. All the best.
Thanks much Grant you remind me of my uncle who had the 1st TV repair shop in the north Adirondacks.That was circa 1950? He was a communications guy in the Marines on Okinawa ww2
You need to know something about the trace geometry to accurately pinpoint the short using this method. You need to measure the voltage drops across the traces. I start by connecting the negative lead of the DMM (mV mode) to the point where the current source's negative terminal connects to the PCB. Then begin probing further from negative connection point until the voltage stops increasing. As long as the voltage continues to increase, you are following the flow of current. As soon as it stops increasing and levels off, you've passed the short. If you have a layout viewer, it really helps. Using this technique with boards that have power planes is more difficult. You'll need a high precision DMM to measure micro-volts of change on top of the millivolt voltage that is actually across the shorted component. You may need 6-digits of precision to do this. The relative (delta) button won't help because the meter will use the appropriate scale for the total voltage ("trace voltage drop" + "shorted component voltage drop"). You are only interested in the trace voltage drop. I suggest using a good cad viewer that allows you to highlight nets and has coordinates so you can calculate distance. I've used this technique to get me within about 1/2 inch of a shorted cap between Vcc and Gnd on boards with hundreds of bypass caps on them. I also use thermal LCD paper and cold spray to try to locate the shorted part thermally.
In India, we mostly use rosin paste and 3.3v with few good range of amps (current) and volts depends to the supply line or supply track. And we easily find the shorting component. There are many ways to locate the shorting component and those are effective too.
I'm a retired avionics tech. 30 years ago HP published a trick not unlike your own, using the mv on the DVM, but with no guessing. To find the short connect a current limited supply to the shorted supply rail at the spec voltage but with a safe current limit. Now connect the positive lead to the rail, and we'll use the neg probe to chase down the short. Clearly the millivoltage will grow towards the short, and if you probe past a node, the voltage will stop increasing.
That's how I used to find shorts until I got a $200 FLIR that connects to my phone. Now one of the first things I do is take pictures of the board temperature signature when I first power up the item. Sometimes it pinpoints the problem without any troubleshooting.
Nice job. I'm working on a small board with a short somewhere. I'm going to apply a small voltage (3 D batteries, 4.5v) with a small current limiting resistor and try to get closest to the short with digital voltmeter readings OR allow more current and feel for a hot component.
GREAT VIDEO & A GREAT LITTLE TRICK! My Teague ESI will measure down to micro-ohms, and uses a 4 lead shielded Kelvin clip lead set. That Teague is around $3000-$5000, used. The time it saves testing caps, & diodes in circuit are kind of worth it. I really love having it, and don't know how I lived without one as long as I did. I have used this method too. I liked the LCR bridge so much, I bought a spare one. It is a Chinese made no name that cost $700, but it works, despite only having 4 test frequencies, 4 test voltages & 4 test current. The Teague has 100s. I fixed up a Samsung plasma TV only to find it puts out excessive RF interference into the mains, making my amateur radio station noisy. Plasma TVs are notorious for backfeeding RF noise into the power lines.
Great video, thanks! There's a potential (little) goldmine out there if you can get the "throwaways" before the "scrappers". And if they are repairable. I bet most are.
this is nice. thank you. I been back to watch this video several time. I also have the toneohm, which, I am in the process of making my own leads since its leads are crazy expensive, I am yet to learn how to use it though.. but I have found using a good thermal camera, though expensive but is a very effecting and fast way in finding shorts. I would call thermal camera, short finder for dummies.
Thank you so much. unfortunately, my bench power supply doesn't control current that accurately so I created a simple constant current supply circuit that I use now for this method.
One can also pour some Butane on the suspect component. The S/C will obviously generate some heat, which in turn will cause the Butane to evaporate (boil) at a rapid rate in comparison to the normally operating components. Of course a Power supply is used for the power source as described in this video. The Current (I) may have to be increased to 5A so that enough heat is generated, As the S?C component is already defective 5A will not be of a concern, and power rail components are quite durable for obvious reasons. For those just learning, it is important to understand how Power rails work, and how lower voltages are derived from the source power rail(s) Not knowing that would be chasing one's own tail and wasting time. Good luck everyone.
Great way to test for shorted components BUT that's IF you have more than one of the same component [with which to compare it with - like three similar values diodes]. But how can this work, when the components are of different values to each other AND altogether different components? Ex: a transistor, a cap [tear shaped - tantalum], an electrolytic cap, few resistors and maybe a diode. What can you possibly achieve test-wise with this method [ESR meter]? You would never be able to find the shorted component. But I have so much more to learn about electronics [I'm a complete NOOB in this field] so, PLEASE correct me if I'm wrong - I truly am trying to learn. Your videos have been a great source of education for me. Thank you kindly.
I fixed my MacBook Air with this method. It had shorted component somewhere on the main power rail to ground. Supposedly, capacitor. But which one of many (about 100)? I put about 0.5V 1A to the board and then started to measure all capacitors to find one with the least voltage on it (because it will be the shorted one). And I found it! With simple cheap multimeter and power supply.
I'm not sure I understand what you're looking for... Every measure you did had different values for different diodes. You KNOW one of the diodes is bad in this case, but the only indication you have for which one it is would be the one with the lowest value in whatever measurement you're doing. But if you don't know if it's a diode or a capacitor (or any other component, for that matter) that is the culprit, how would this help you? You haven't really located the short, because to even use the technique, you must know which component type you're looking for. And even then, it only works if all of the components of that type in the circuit has the same value. And even then, you can get "false positives" because of the natural difference in the readings.
This procedure is designed to help you find a shorted component where there are multiple components which share the same power supply output. it's not going to tell you if a diode, capacitor, IC, or transistor is open, but if one of these components is shorted such as a diode it will have the lowest voltage drop of all the components you test. I hope this helps.
Hey, you can just supply this troubled PCB not with ordinary high input voltage but with low voltage and high current capability power supply. And just use your fingertip to locate a shorted component(s) by its temperature. )) Any advanced multimeter needed, but ATC 300W power supply in tact is strongly recommended to have in your workbench.
very good most helpfull tip haow can you check for a winding short in a transformer do you have to use a micro ohm meter and know what a good one would read?
I do have a micro ohm meter, but when I test the primary side of a transformer I often use the my blue ring coil tester. Here is video on how they work. th-cam.com/video/Ky2T1-n_Fks/w-d-xo.html
Hi Dave , I to enjoy finding shorts to ground, and use two different approaches depending the mood i' m in 1st is my home made milliohm meter, other more recently is a circuit I found on the web current source .25 of a watt at 3 volts, so I use that method you used, works well, to practise on I have some old tv boards, which I know have faults, so I quite moment & I try these things out, I haven't yet tried out the ESR meter, but may well Paul M0BSW uk
Gustav Kirchhoff would turn in his grave if he saw this video...... Those components are in parallel , the voltage drop across the components will be identical as you are measuring rail to rail. They will be passing different currents depending on their resistance but the voltage drop across the rails will be the same no matter where you measure. The more sensitive you make your meter readings, the more you will think that a few millivolts here or there mean something when they actually dont.. There is a reason why components in parallel need to be unsoldered to check, and this is a good lesson in why.
omgffsification Technically speaking the only voltage drop you really see in this example is from the shorted diode. The other diodes direction are not in the conduct mode, and capacitors do not pass DC. I should have used slightly different words to describe this example.
When diodes go bad they generally short out and their resistance goes down as the diode junctions become fused together. This test is showing me which diode has the lowest resistance reading within a few thousandths of an ohm.
seems like way more work than just to take your chances and start snipping a few anode leads until your short is gone. then a dab of solder to reconnect the innocent components
There have been time in the past where I actually used the most simple and cheapest piece of test equipment I have. With a current limited supply and a little bit of current I used my finger to find who's getting hot... ;-)
We have a variety of ways to accomplish the same end result when looking for shorts to ground. Sometimes I use a lazier temperature probe, or I freeze spray the whole board until it turns white, and then watch to see which components are the fist to defrost. Louis Rossman made a video where he poured alcohol on his circuit board, and then watched to see which area of the board evaporated first.
LoL that is kinda funny, I thought you were gonna say where the alcohol starts sizzling... Yeah we are a creative group sometimes. More then most other groups....
hi, is there a difference between a bad diode and a shortened diode when checked with a meter what i am asking would a shortened diode measure as bad with a meter ? thank you
I don't quite understand your question, but I think you meant to say shorted diode rather than shortened diode. ;-). When the short out they generally become like a piece of wire with almost no measurable resistance. Less than 1 ohm.
Actually, there is one thing here VERY WRONG. Measuring with current is ok, but 0.25A is TOO MUCH - that could've fried your diodes! Most diodes work on currents around 20mA (LED diodes for example) and that is a level you should have. In this example you where lucky that the diodes you had there where power diodes, but on laptop motherboards and elsewhere, the diodes are much more sensitive and they can get fried with as low current as 50mA. Of course, a short to the ground means that the power will go through the short and not through the diodes, but once the short is gone, all that power would go to those diodes. Another safe thing (except limiting current) would be to try to find the short by limiting the voltage to 0.25 V - at this voltage most of the diodes just don't work and no harm will happen to them even if the short will be eliminated. At 0.25V only thing that works is passive components (and shorts) - and those can handle that voltage no problem, so you don't have to limit the current so much when you are at 0.25V.
Yes there are some components such as LEDs that can easily be damaged with 0.25 of an amp, but If you insert a low voltage directly across one of the electrolytic capacitors on the circuit trace in question, and apply the correct polarity your not likely to damage anything. Especially when you consider there is already a short dragging your voltage way down below normal operating voltages. If I see an electrolytic capacitor on the circuit trace I'm testing with a working voltage printed on the side, I think it's fair to assume I can safely apply 10 percent of that voltage and probably much more without causing any additional problems. Even if the short were to open, as long as you don't exceed the normal operating voltage of the circuit and you apply the correct polarity it should be fine.
Thanks for this great video. I learned something new today. It just happens that I have an incredibly expensive board that has a short on it's power bus. I am dying to try out this new method of tracing it. Please let it not be the CPU, because then it's fucked.
Never mind. I was thinking you could use Nano Siemens which can be used to measure very hi resistance. In this case your measuring very low resistance. My fault. Thanks
If it's a shorted part other than a diode, the same technique can apply, but unless you have a schematic, or a pinout of the part, it can be more challenging to isolate which part or parts have gone bad, When transistors go bad their terminals often short out between them, so using an ohm meter can also help you isolate the problem by looking for shorts between the transistor terminals. Having a schematic can help you understand what's likely to be a shorted part if you measure a low resistance path to ground on a component terminal that should show an open relative to ground of your power supply, and learning to read schematics can be a time saver if you happen to have one for the device you're trying to repair, and knowing which parts are more likely to fail can also be helpful. The parts which mostly commonly fail are diodes, transistors and ICs. It's been my experiences that electrolytic capacitors rarely short out, but sometimes the small surface mounted capacitors are known to short out.
That's exactly my problem. I have a short on the board I'm working on, but I suspect the issue is a ymf292f sound chip, for which I can't find a schematic or a replacement! Thanks for the response.@@GrantsPassTVRepair
Have any idea how I can force yt to put up your newest videos? I go out of town and upon returning yt seems to "retire" subscriptions to the back burner. I imagine just finding and watching a few is the only way.
That depends on how much resistance the shorted component has once it goes bad. As a general rule when a diode goes bad it will have less than One ohm of resistance, so it's about the same as a piece of wire.
The voltage drop across a wire is very small, but it is never zero volts. All wires have resistance. That's why this technique works. Shorted components often have more voltage drop than a wire does.
Great video sir. But I have this question: you say "...when it senses a short, the feedback circuit slows down the duty cycle..." Which particular component, in the feedback circuit does the "sensing" exactly? Please let me know. Keep making videos and be safe out there. Cheers!
Thank you, for replying. Pardon my ignorance, I'm a complete NOOB but do you mean, that opto isolator are used to alter the duty cycle of power supplies OR that opto isolator are used to NOT alter the duty cycle - make it more stable. Please reply, I want to learn. Thank you kindly and be well
@@maxwarfield6699 Opto Isolators are used to help regulate the power from a switching power supply by monitoring the output power and sending a sample to other ICs for regulation. If you youtube opto isolators you can learn a great deal more than I can explain in a few lines of text.
I would think a component shorted to ground would have no voltage drop across the component. Doesn’t the shorted component just become a low resistance wire, therefore no voltage drop across it .
Your correct about a shorted component becoming like a low resistance wire, but if you measure across the component input wires with a voltage applied to the component you will see more of a voltage drop than you would with a non shorted component.
Think about this concept. You attach a 10 volt battery to Two parallel wires that are 5 feet long, and at the end of the 5 foot stretch of wires you attach a 1 ohm resistor. If you measured your battery voltage right at the battery terminals it would read higher than the voltage you would read across the resistor due to the voltage drop across the resistor. If you did this same experiment using a 10 ohm resistor you would have less of a voltage drop, and you would read a higher voltage than you would using the 1 ohm resistor. I hope this example helps.
Adhesive copper tape. Available everywhere, here is a link to one site that sells it, there are other sites, or outlets in your country as well. www.sparkfun.com/products/10561
I am wondered when looking at your demo when you turn ON DC power supply and connected to a short circuit that you made it by your own. I think it would feedback and blow power supply if you leave it for a certain time. THX,
Yes it could be a problem if your asking the power supply to deliver more amps than it can handle. My power supply can deliver up to 3 amps with out there being a problem to my power supply. If your power supply can't handle what ever current a short circuit produces, you can add a resistor in series with the device your attempting to repair. You resistor will probably get hot if your device has a short so you may need a high wattage resistor.
it is exactly you need to mention in your demo, if there are someone do not know would cause lot problem. Also, You forgot to let reader know the method measure Diode by reversing the lead of DVM, Thanks,
+VINCENT ONGALA Most of the time you can test diodes which are in circuit, but sometimes you must remove them to know if they are shorted due to the surrounding components on the board . Anytime you remove a diode which appears to be shorted it's always a good idea to test them out of circuit to make sure your test results were not effected by surrounding components. Most of the time a shorted diode will have less than 1 ohm of resistance, so when I get a bad reading using the diode check function of my multimeter I switch my meter over to the ohms function so I can get more information about the nature of the short in terms of how much resistance the diode appears to have in circuit. If the ohms reading is 10 ohms or more I generally assume the diode is probably okay, but when in doubt pull them out to double test.
Yes. If you know where to test such as a positive power rail that should never have an extremely low resistance reading to ground. If you don't know where to test on the circuit board you can check for shorts across your capacitors. If you get an extremely low resistance reading it means you have a shorted capacitor or something on the circuit in parallel with the capacitor may be shorted.
I like you video, this the second time I watch it because i am trying to find a short. little confusing, you measured across 3 diodes at about 1.04 mv. then you measure the shorted diode at 0.64 and you said you would know this is shorted because it has a much greater voltage drop. how is that greater voltage drop. isn't 1.04 mv is greater than 0.64.
@@jacka.4774Do you understand how 0.1 is Ten times smaller than 1? When I'm testing for voltage drop across each diode I'm trying to figure out which diode reads the smallest number to figure out which diode is shorted.
@@GrantsPassTVRepair thank you. so could you see if I understand it correctly. if shorted you read lower voltage across diode compared to the same ones. same as measuring voltage across the same short piece of wire.
@@jacka.4774 Yes, it sounds like you understand correctly. When diodes go bad they often short out and become much like a small piece of wire, and you will see their resistance will generally measure One ohm or less. They can open also open up inside, but that's far less common.
You said the diodes are in parallel so if one is shorted then they all are?? My question is what reason would they be in parallel if they all fall short when one fall short.
@@irishguy200007 I don't recall saying that all of the diodes will be shorted just because one of them was bad. My point was that one shorted diode is in parallel with other diodes it can make it appear as though all of the diodes are shorted. Unless you have a sensitive meter it will be difficult to figure out which one of them is actually bad.
it is cheaper to replace circuit board some time than spend time and money locating tbl. keep this in mind when cust is paying by the hour you can shaft him one time but he want come back
@@GrantsPassTVRepair Had to troubleshoot a part that was drawing curent on an old PC board. There are some 40+ ICs. Some were getting hot, others not. But by using a ohmmeter, i was able to locate the problem in the memory area. After removing the memory chips, the problem was gone. The memory chips were not getting very hot.
Longer leads on a ESR meter just doesn't work. The meter gives you an error message when trying to calibrate to "0", probably due to the capacitance of the cables themselves? That's why all ESR meters that I know of, have short leads (too short, yes :)
@@Cubasenet33, You are correct, the ESR meter leads do add capacitance, hence they are short. I tried adding longer leads to mine as an experiment, and it does change your readings.
Dave, I was hoping to see a really informative video, but you spoilt it by having it all OUT OF FOCUS. Also, I need to read your multimeter setting position and you had an elestic bungee across the selector knob obscuring the view. What a shame. Keith 😞
I was just searching to see how to put a multimeter to millivolts and seen this video. I finally see how diode measured to find if they aren’t working. Video is beyond excellent.
I have a digital ESR meter but I never know I could used it in other way just like what you did in this video. Thanks for sparing some time to share us your skills sir.
What a fantastic video! Over my self-educated time spent (100's and 100's of videos and some books), what no one ever said/wrote was that in repairing electronics, it all comes down to OPENs and SHORTs; with SHORTS being the "variable" cause ... meaning that there can be a SHORT ...or... a PARTIAL SHORT that's causing the problem. Once that became apparent, troubleshooting changed to "much easier" to diagnose. I have a Zapper, built a LeakSeeker, have injected voltage, and and and. This video from 7yrs ago ... I wished I had discovered earlier. It added a very valuable approach ... inject a small voltage and then look for a voltage drop in the mA's (or maybe even uA's if you can). Brilliant. Thanks for this video.
Thank you for the comment. It's always nice to hear when someone appreciates on of my videos. We had a period where bad capacitors kept repairmen fairly busy due to a manufacture error known as the "capacitor plague", but that's not so common anymore, so other than bad eeproms and leaky parts, I suppose shorts and opens do make up the bulk of repairs. All the best.
Thanks much Grant you remind me of my uncle who had the 1st TV repair shop in the north Adirondacks.That was circa 1950? He was a communications guy in the Marines on Okinawa ww2
This technique works very well, great on logic circuits were the 5v rail might go everywhere.
Great idea for locating shorts to ground; in fact you have given me an idea that I want to try out when I come across this situation again.
You need to know something about the trace geometry to accurately pinpoint the short using this method. You need to measure the voltage drops across the traces.
I start by connecting the negative lead of the DMM (mV mode) to the point where the current source's negative terminal connects to the PCB. Then begin probing further from negative connection point until the voltage stops increasing. As long as the voltage continues to increase, you are following the flow of current. As soon as it stops increasing and levels off, you've passed the short. If you have a layout viewer, it really helps.
Using this technique with boards that have power planes is more difficult. You'll need a high precision DMM to measure micro-volts of change on top of the millivolt voltage that is actually across the shorted component. You may need 6-digits of precision to do this. The relative (delta) button won't help because the meter will use the appropriate scale for the total voltage ("trace voltage drop" + "shorted component voltage drop"). You are only interested in the trace voltage drop.
I suggest using a good cad viewer that allows you to highlight nets and has coordinates so you can calculate distance. I've used this technique to get me within about 1/2 inch of a shorted cap between Vcc and Gnd on boards with hundreds of bypass caps on them. I also use thermal LCD paper and cold spray to try to locate the shorted part thermally.
In India, we mostly use rosin paste and 3.3v with few good range of amps (current) and volts depends to the supply line or supply track. And we easily find the shorting component. There are many ways to locate the shorting component and those are effective too.
I'm a retired avionics tech. 30 years ago HP published a trick not unlike your own, using the mv on the DVM, but with no guessing. To find the short connect a current limited supply to the shorted supply rail at the spec voltage but with a safe current limit. Now connect the positive lead to the rail, and we'll use the neg probe to chase down the short. Clearly the millivoltage will grow towards the short, and if you probe past a node, the voltage will stop increasing.
I'm not to surprised. Unless you own a low ohm meter capable of 1000 divisions it's a great option.
That's how I used to find shorts until I got a $200 FLIR that connects to my phone. Now one of the first things I do is take pictures of the board temperature signature when I first power up the item. Sometimes it pinpoints the problem without any troubleshooting.
@@RickNickel hi Rick would you post a link to this?
@@RickNickel Looking at one today for the same purpose.
it kinda like the opposite of what he is doing very smart!!!
So simple yet so brilliant! Thanks for sharing.
Excellent way to find shorts !! I had one in my house wiring that I found with your method. Thanks !!!
The ESR meter should be enough to find the culprit. Indeed a must have tool
I've learnt something from you every video I've watched, thank you.
Usually to find shorts of that kind, i usually plug a lab supply across the shorted rail and inject some power and look for the hot parts.
***** I've used the same technique, but sometimes it takes quite a bit of current to get the component to warm up.
Excellent information! Thank you for sharing your knowledge with all of us! Fred
I'm just getting into electronics learning Arduino and this video is helpful.
Hi Dave
Another great Video. Thank you for taking the time to show us your troubleshooting tricks. Keep up the great work you are doing.
Cheers
Willy
Nice job. I'm working on a small board with a short somewhere. I'm going to apply a small voltage (3 D batteries, 4.5v) with a small current limiting resistor and try to get closest to the short with digital voltmeter readings OR allow more current and feel for a hot component.
Thank you i have been trying to do a similar check with sm caps in parallel☺
Thank you! Gives me some more ideas. Shout out from Coos County!
GREAT VIDEO & A GREAT LITTLE TRICK! My Teague ESI will measure down to micro-ohms, and uses a 4 lead shielded Kelvin clip lead set. That Teague is around $3000-$5000, used. The time it saves testing caps, & diodes in circuit are kind of worth it. I really love having it, and don't know how I lived without one as long as I did. I have used this method too. I liked the LCR bridge so much, I bought a spare one. It is a Chinese made no name that cost $700, but it works, despite only having 4 test frequencies, 4 test voltages & 4 test current. The Teague has 100s. I fixed up a Samsung plasma TV only to find it puts out excessive RF interference into the mains, making my amateur radio station noisy. Plasma TVs are notorious for backfeeding RF noise into the power lines.
Great video, thanks! There's a potential (little) goldmine out there if you can get the "throwaways" before the "scrappers". And if they are repairable. I bet most are.
I like the ones with broken screens, if they come on ther usually some fairly good boards inside.Sometimes it's deceiving.
Big thanks for these very powerfull techniques, voltage drop is really revealing
I'm glad you found this technique helpful. Thanks for the comment.
this is nice. thank you. I been back to watch this video several time. I also have the toneohm, which, I am in the process of making my own leads since its leads are crazy expensive, I am yet to learn how to use it though.. but I have found using a good thermal camera, though expensive but is a very effecting and fast way in finding shorts. I would call thermal camera, short finder for dummies.
Way above my skill level but I'm always happy to meet a person that knows more than me.
I try to keep it simple so anyone can follow along, but perhaps I can do a little better.
Thanx for the video very useful & educational !!! Keep them rolling my friend
Thank you so much. unfortunately, my bench power supply doesn't control current that accurately so I created a simple constant current supply circuit that I use now for this method.
Very good teacher.
MrMac5150 Thanks.
send some more of your skills this way.
One can also pour some Butane on the suspect component.
The S/C will obviously generate some heat, which in turn will
cause the Butane to evaporate (boil) at a rapid rate in comparison
to the normally operating components.
Of course a Power supply is used for the power source as described
in this video. The Current (I) may have to be increased to 5A so that
enough heat is generated,
As the S?C component is already defective 5A will not be of a concern,
and power rail components are quite durable for obvious reasons.
For those just learning, it is important to understand how Power rails work,
and how lower voltages are derived from the source power rail(s)
Not knowing that would be chasing one's own tail and wasting time.
Good luck everyone.
A thermal camera would have being really nice
Well done. I have not used this technique, but you can bet that I will.
Great way to test for shorted components BUT that's IF you have more than one of the same component [with which to compare it with - like three similar values diodes]. But how can this work, when the components are of different values to each other AND altogether different components? Ex: a transistor, a cap [tear shaped - tantalum], an electrolytic cap, few resistors and maybe a diode. What can you possibly achieve test-wise with this method [ESR meter]? You would never be able to find the shorted component. But I have so much more to learn about electronics [I'm a complete NOOB in this field] so, PLEASE correct me if I'm wrong - I truly am trying to learn. Your videos have been a great source of education for me. Thank you kindly.
Excellent Dave.
I fixed my MacBook Air with this method. It had shorted component somewhere on the main power rail to ground. Supposedly, capacitor. But which one of many (about 100)?
I put about 0.5V 1A to the board and then started to measure all capacitors to find one with the least voltage on it (because it will be the shorted one).
And I found it! With simple cheap multimeter and power supply.
this is a great way to find bad connections on car battery leads
ESR meter can also read very small value resistors.
Very very helpful , thank u , hope u get time to make some more videos soon , I enjoy watching them
I'm not sure I understand what you're looking for... Every measure you did had different values for different diodes. You KNOW one of the diodes is bad in this case, but the only indication you have for which one it is would be the one with the lowest value in whatever measurement you're doing.
But if you don't know if it's a diode or a capacitor (or any other component, for that matter) that is the culprit, how would this help you? You haven't really located the short, because to even use the technique, you must know which component type you're looking for. And even then, it only works if all of the components of that type in the circuit has the same value. And even then, you can get "false positives" because of the natural difference in the readings.
This procedure is designed to help you find a shorted component where there are multiple components which share the same power supply output. it's not going to tell you if a diode, capacitor, IC, or transistor is open, but if one of these components is shorted such as a diode it will have the lowest voltage drop of all the components you test. I hope this helps.
Finally.....thank you SIr
Yes it helped, Thank you so much
Thank you for a good video!
Thanks Dave. I appreciate the video.
excellent, thank you for sharing your hard earned knowledge, much respect!
Thanks! helped me find the needle in a haystack.. bad SMT cap
Hey, you can just supply this troubled PCB not with ordinary high input voltage but with low voltage and high current capability power supply. And just use your fingertip to locate a shorted component(s) by its temperature. )) Any advanced multimeter needed, but ATC 300W power supply in tact is strongly recommended to have in your workbench.
This was really helpfull, thank you.
very good most helpfull tip haow can you check for a winding short in a transformer do you have to use a micro ohm meter and know what a good one would read?
I do have a micro ohm meter, but when I test the primary side of a transformer I often use the my blue ring coil tester. Here is video on how they work. th-cam.com/video/Ky2T1-n_Fks/w-d-xo.html
Great video
Hi Dave , I to enjoy finding shorts to ground, and use two different approaches depending the mood i' m in 1st is my home made milliohm meter, other more recently is a circuit I found on the web current source .25 of a watt at 3 volts, so I use that method you used, works well, to practise on I have some old tv boards, which I know have faults, so I quite moment & I try these things out, I haven't yet tried out the ESR meter, but may well
Paul M0BSW uk
Thanks for the info. I miss the days when searching for shorts to ground was a regular necessity.
The noise is caused by pulse skipping. Even a minimum pulse width PWM will be inaudible because the switching frequency doesn’t change.
Another great education. Thanks!
11:03, *smaller* voltage drop. I know you knew that... (c:
Thank you , great tip!
Very helpful video! Thank you!
Very useful. Thank you.
Gustav Kirchhoff would turn in his grave if he saw this video......
Those components are in parallel , the voltage drop across the components will be identical as you are measuring rail to rail. They will be passing different currents depending on their resistance but the voltage drop across the rails will be the same no matter where you measure.
The more sensitive you make your meter readings, the more you will think that a few millivolts here or there mean something when they actually dont..
There is a reason why components in parallel need to be unsoldered to check, and this is a good lesson in why.
omgffsification Technically speaking the only voltage drop you really see in this example is from the shorted
diode. The other diodes direction are not in the conduct mode, and capacitors do not pass DC. I should have used slightly different words to describe this example.
Grants Pass TV Repair Sure but how is this test telling you which diode is shorted?
When diodes go bad they generally short out and their resistance goes down as the diode junctions become fused together. This test is showing me which diode has the lowest resistance reading within a few thousandths of an ohm.
NICE . ThanX !!!
seems like way more work than just to take your chances and start snipping a few anode leads until your short is gone. then a dab of solder to reconnect the innocent components
Clipping leads or un-soldering multiple diodes sounds far more labor intensive than a few quick probes with a low ohm meter,
thank you nicely explained.
There have been time in the past where I actually used the most simple and cheapest piece of test equipment I have. With a current limited supply and a little bit of current I used my finger to find who's getting hot... ;-)
We have a variety of ways to accomplish the same end result when looking for shorts to ground. Sometimes I use a lazier temperature probe, or I freeze spray the whole board until it turns white, and then watch to see which components are the fist to defrost. Louis Rossman made a video where he poured alcohol on his circuit board, and then watched to see which area of the board evaporated first.
LoL that is kinda funny, I thought you were gonna say where the alcohol starts sizzling... Yeah we are a creative group sometimes. More then most other groups....
hi, is there a difference between a bad diode and a shortened diode when checked with a meter what i am asking would a shortened diode measure as bad with a meter ? thank you
I don't quite understand your question, but I think you meant to say shorted diode rather than shortened diode. ;-). When the short out they generally become like a piece of wire with almost no measurable resistance. Less than 1 ohm.
Actually, there is one thing here VERY WRONG.
Measuring with current is ok, but 0.25A is TOO MUCH - that could've fried your diodes!
Most diodes work on currents around 20mA (LED diodes for example) and that is a level you should have.
In this example you where lucky that the diodes you had there where power diodes, but on laptop motherboards and elsewhere, the diodes are much more sensitive and they can get fried with as low current as 50mA.
Of course, a short to the ground means that the power will go through the short and not through the diodes, but once the short is gone, all that power would go to those diodes.
Another safe thing (except limiting current) would be to try to find the short by limiting the voltage to 0.25 V - at this voltage most of the diodes just don't work and no harm will happen to them even if the short will be eliminated.
At 0.25V only thing that works is passive components (and shorts) - and those can handle that voltage no problem, so you don't have to limit the current so much when you are at 0.25V.
Yes there are some components such as LEDs that can easily be damaged with 0.25 of an amp, but If you insert a low voltage directly across one of the electrolytic capacitors on the circuit trace in question, and apply the correct polarity your not likely to damage anything. Especially when you consider there is already a short dragging your voltage way down below normal operating voltages.
If I see an electrolytic capacitor on the circuit trace I'm testing with a working voltage printed on the side, I think it's fair to assume I can safely apply 10 percent of that voltage and probably much more without causing any additional problems. Even if the short were to open, as long as you don't exceed the normal operating voltage of the circuit and you apply the correct polarity it should be fine.
@@GrantsPassTVRepair the short acts like a dim bulb device?
The short is preventing your power supply output from passing through the circuit it's intended to pass through. @@fullwaverecked
Thanks for this great video. I learned something new today. It just happens that I have an incredibly expensive board that has a short on it's power bus. I am dying to try out this new method of tracing it. Please let it not be the CPU, because then it's fucked.
cheer's another couple of top tip's
Thank you!
New subscriber here.
Great Video .
Thanks
very informative video
Could you also use nS to measure conductance and then convert it to ohms? For small resistances. The fluke 87v has nS but is kinda hidden.
I don't understand your question.
Never mind. I was thinking you could use Nano Siemens which can be used to measure very hi resistance. In this case your measuring very low resistance. My fault. Thanks
Well that's great if you short is because of a bad diode. What do you do if it's NOT a diode?
If it's a shorted part other than a diode, the same technique can apply, but unless you have a schematic, or a pinout of the part, it can be more challenging to isolate which part or parts have gone bad, When transistors go bad their terminals often short out between them, so using an ohm meter can also help you isolate the problem by looking for shorts between the transistor terminals. Having a schematic can help you understand what's likely to be a shorted part if you measure a low resistance path to ground on a component terminal that should show an open relative to ground of your power supply, and learning to read schematics can be a time saver if you happen to have one for the device you're trying to repair, and knowing which parts are more likely to fail can also be helpful. The parts which mostly commonly fail are diodes, transistors and ICs. It's been my experiences that electrolytic capacitors rarely short out, but sometimes the small surface mounted capacitors are known to short out.
That's exactly my problem. I have a short on the board I'm working on, but I suspect the issue is a ymf292f sound chip, for which I can't find a schematic or a replacement! Thanks for the response.@@GrantsPassTVRepair
how value voltage and current to charge? for not damage the other component
Have any idea how I can force yt to put up your newest videos? I go out of town and upon returning yt seems to "retire" subscriptions to the back burner. I imagine just finding and watching a few is the only way.
madisonelectronic I put an index to all my youtube videos at www.tvrepairinfo.com/
Wouldn't the voltage drop across a shorted component be zero volts? I was told it acts like a wire.
That depends on how much resistance the shorted component has once it goes bad. As a general rule when a diode goes bad it will have less than One ohm of resistance, so it's about the same as a piece of wire.
The voltage drop across a wire is very small, but it is never zero volts. All wires have resistance. That's why this technique works. Shorted components often have more voltage drop than a wire does.
Great video sir. But I have this question: you say "...when it senses a short, the feedback circuit slows down the duty cycle..." Which particular component, in the feedback circuit does the "sensing" exactly? Please let me know. Keep making videos and be safe out there. Cheers!
I can't give you specifics on every component used to alter the duty cycle of a power supply, but Opto isolators are often used for shis purpose.
Thank you, for replying. Pardon my ignorance, I'm a complete NOOB but do you mean, that opto isolator are used to alter the duty cycle of power supplies OR that opto isolator are used to NOT alter the duty cycle - make it more stable. Please reply, I want to learn. Thank you kindly and be well
@@maxwarfield6699 Opto Isolators are used to help regulate the power from a switching power supply by monitoring the output power and sending a sample to other ICs for regulation. If you youtube opto isolators you can learn a great deal more than I can explain in a few lines of text.
You're AWESOME, thanks! And I will look up opto isolator, I have to get to the bottom of this. Thanks again mate. Cheers!
I would think a component shorted to ground would have no voltage drop across the component. Doesn’t the shorted component just become a low resistance wire, therefore no voltage drop across it .
Your correct about a shorted component becoming like a low resistance wire, but if you measure across the component input wires with a voltage applied to the component you will see more of a voltage drop than you would with a non shorted component.
Grants Pass TV Repair I thought less resistance less voltage drop. Ie. no load, no voltage drop.
Think about this concept. You attach a 10 volt battery to Two parallel wires that are 5 feet long, and at the end of the 5 foot stretch of wires you attach a 1 ohm resistor. If you measured your battery voltage right at the battery terminals it would read higher than the voltage you would read across the resistor due to the voltage drop across the resistor. If you did this same experiment using a 10 ohm resistor you would have less of a voltage drop, and you would read a higher voltage than you would using the 1 ohm resistor. I hope this example helps.
Good video. Thanks!.
Wow! Now I know. Thanks
whats the type of the "paper" that connects resistors
you use for simulation? thank you!
Adhesive copper tape. Available everywhere, here is a link to one site that sells it, there are other sites, or outlets in your country as well. www.sparkfun.com/products/10561
Should I connect the VDC power to a short circuit as your demo???
+Hiem Ngo I'm not sure I understand your question.
I am wondered when looking at your demo when you turn ON DC power supply and connected to a short circuit that you made it by your own. I think it would feedback and blow power supply if you leave it for a certain time. THX,
Yes it could be a problem if your asking the power supply to deliver more amps than it can handle. My power supply can deliver up to 3 amps with out there being a problem to my power supply. If your power supply can't handle what ever current a short circuit produces, you can add a resistor in series with the device your attempting to repair. You resistor will probably get hot if your device has a short so you may need a high wattage resistor.
it is exactly you need to mention in your demo, if there are someone do not know would cause lot problem. Also, You forgot to let reader know the method measure Diode by reversing the lead of DVM,
Thanks,
Awesome, thanks.
good information
The best short detecter for the circuit you’ve shown is your finger.
Mitsubishi #WS-5561 Turns off then can turn on again may work for ??? time. Then turn off again. No green blinking.
can a diode be tested when still atteched to the board?
+VINCENT ONGALA Most of the time you can test diodes which are in circuit, but sometimes you must remove them to know if they are shorted due to the surrounding components on the board . Anytime you remove a diode which appears to be shorted it's always a good idea to test them out of circuit to make sure your test results were not effected by surrounding components. Most of the time a shorted diode will have less than 1 ohm of resistance, so when I get a bad reading using the diode check function of my multimeter I switch my meter over to the ohms function so I can get more information about the nature of the short in terms of how much resistance the diode appears to have in circuit. If the ohms reading is 10 ohms or more I generally assume the diode is probably okay,
but when in doubt pull them out to double test.
Nice
can we use this method to find a short on a Laptop mother board?
Yes. If you know where to test such as a positive power rail that should never have an extremely low resistance reading to ground. If you don't know where to test on the circuit board you can check for shorts across your capacitors. If you get an extremely low resistance reading it means you have a shorted capacitor or something on the circuit in parallel with the capacitor may be shorted.
Thanks for this vedio
VERY GOOD
Seen a lot of this kind of psu fault... I just desolder the doides and check... These types are 5a diodes..
That's One of many ways to do it.
I like you video, this the second time I watch it because i am trying to find a short. little confusing, you measured across 3 diodes at about 1.04 mv. then you measure the shorted diode at 0.64 and you said you would know this is shorted because it has a much greater voltage drop. how is that greater voltage drop. isn't 1.04 mv is greater than 0.64.
1.04 is larger than 0.64. The smaller fraction indicate more of a voltage drop.
@@GrantsPassTVRepair thank you. mmm I got to wait a while before that one settles in my mind.
@@jacka.4774Do you understand how 0.1 is Ten times smaller than 1? When I'm testing for voltage drop across each diode I'm trying to figure out which diode reads the smallest number to figure out which diode is shorted.
@@GrantsPassTVRepair thank you. so could you see if I understand it correctly. if shorted you read lower voltage across diode compared to the same ones. same as measuring voltage across the same short piece of wire.
@@jacka.4774 Yes, it sounds like you understand correctly. When diodes go bad they often short out and become much like a small piece of wire, and you will see their resistance will generally measure One ohm or less. They can open also open up inside, but that's far less common.
Thanks
Nice idea ;-)
I have short killer pro HR1520
thanku
The old way worked better; you're going to want to change all the rectifiers and capacitors anyway. What is it, about $5 worth of parts?
Why are the diodes in parallel
Where?
You said the diodes are in parallel so if one is shorted then they all are??
My question is what reason would they be in parallel if they all fall short when one fall short.
@@irishguy200007 I don't recall saying that all of the diodes will be shorted just because one of them was bad. My point was that one shorted diode is in parallel with other diodes it can make it appear as though all of the diodes are shorted. Unless you have a sensitive meter it will be difficult to figure out which one of them is actually bad.
@@GrantsPassTVRepair So they put these diodes in parallel to take higher current??
@@irishguy200007 I don't know why many of the diodes were in a parallel circuit,
it is cheaper to replace circuit board some time than spend time and money locating tbl. keep this in mind when cust is paying by the hour you can shaft him one time but he want come back
Or, You can use the ohm meter.
With a sensitive ohm meter that gives you 100 to 1000 divisions you can.
@@GrantsPassTVRepair Had to troubleshoot a part that was drawing curent on an old PC board.
There are some 40+ ICs.
Some were getting hot, others not.
But by using a ohmmeter, i was able to locate the problem in the memory area.
After removing the memory chips, the problem was gone. The memory chips were not getting very hot.
needs longer leads on esr meter
Longer leads on a ESR meter just doesn't work. The meter gives you an error message when trying to calibrate to "0", probably due to the capacitance of the cables themselves? That's why all ESR meters that I know of, have short leads (too short, yes :)
@@Cubasenet33, You are correct, the ESR meter leads do add capacitance, hence they are short. I tried adding longer leads to mine as an experiment, and it does change your readings.
Thanks. But quality video - i broken my yeys, change camera pls
My multimeter's R5 has blown
Dave, I was hoping to see a really informative video, but you spoilt it by having it all OUT OF FOCUS. Also, I need to read your multimeter setting position and you had an elestic bungee across the selector knob obscuring the view. What a shame. Keith 😞