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 Post subject: Finding shorted parts
PostPosted: Sep Tue 07, 2021 6:59 pm 
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Joined: Nov Sun 07, 2010 7:16 pm
Posts: 859
Location: Manchester, MI
This topic shows up once in a while, mostly in regards to solid state equipment (which also can be antiques at this time) and tracking down the problem can be difficult. There are tools to help, things like milliohm meters, audible short seekers, etc. Many people may either not have one of these tools or may not want to take on yet another project to build their own. The other day i ran across an interesting article that shows how you can use a basic DMM (preferably one than can resolve 1 mV), a flashlight battery and a resistor to track down shorted parts.

Here's a link to the article at EDN, it explains the technique way better than I can. I can say that it is an extremely clever application of basic principles

https://www.edn.com/quickly-find-pc-boa ... technique/

So the next time you have a shorted power rail with dozens of potential culprits and no access to fancy equipment, here's a technique that will save you a major headache


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 Post subject: Re: Finding shorted parts
PostPosted: Sep Tue 07, 2021 7:43 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 1519
An ESR tester also works great for finding shorts.

DM


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 Post subject: Re: Finding shorted parts
PostPosted: Sep Wed 08, 2021 12:04 am 
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Joined: Mar Thu 15, 2018 2:23 pm
Posts: 460
a little spit and a finger works well too...


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 Post subject: Re: Finding shorted parts
PostPosted: Sep Wed 08, 2021 1:41 am 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 11158
Location: Long Island NY
A simpler way is to use the "diode test" function that is included on most new(er) DMMs. Most of them put a low regulated voltage in series with a resistor, and measure the resulting voltage across the probes. This way you know what voltage is across a semiconductor junction when you forward bias it. Used as a short-finder the reading will get closer to zero the closer you get to the shorted component.

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 Post subject: Re: Finding shorted parts
PostPosted: Sep Wed 08, 2021 8:05 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 1616
devilsmist wrote:
An ESR tester also works great for finding shorts.

DM


Yes they do. Specifically , the Bob Parker designed ESR meter. With this meter, you initially short the leads together and zero it, eliminating the test lead resistance as a variable. It uses a pulse method that is superior to sine wave ESR meters.

A link to the best ESR meter ever made on this planet, get one before it becomes unobtainium, which excellent and unique things often do:

https://www.altronics.com.au/p/k2574-esr-meter-kit/


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 Post subject: Re: Finding shorted parts
PostPosted: Sep Wed 08, 2021 9:17 am 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 1126
Location: Stone Mountain, GA
When finding PCB shorts I use a light bulb and a DC supply. Power the shorted board through the light bulb. Shorts between small wires used something like a #47, ground plane shorts used a car brake light.

Then measure voltages along the traces. Where the short is where be the lowest value will be measured between traces. You can also measure along a trace to measure the drop. After the short will be no drop.

Used many times. Now with a current limited supply, I don't need the bulb.

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