the best way to find short circuit?

[shortchange]

Re: the best way to find short circuit?

I would say using your VOM is fine.
All you need to see is a needle movement.
With digits I have to see number change.
That is alot of needle movement.

[senz_90]

Re: the best way to find short circuit?

I would say using your VOM is fine.
All you need to see is a needle movement.
With digits I have to see number change.
That is alot of needle movement.

hm. yeah..
i have ever look googling that buzzer on my VOM could found short cicuitry. ever try it?? i just trying to measure last night, i found that it is still buzz when i trying to connect across 10 ohms resistor. that is no chance if it buzz even with 10 ohms resistor i guess. IMO it must buzz when the resistance is about 0,x i thought..

[Ltank]

Re: the best way to find short circuit?

Most people use DVM a 3.5 digit meter. Can find s short in general but if the parts are interconnected, no matter where you place meter + probe and the gnd probe to gnd, will show. .1 or. 001 for dead short to gnd. Usually inspection reveals a burnt part but it looks Good then a 5.5 or 6.5 digital benchtop meter is reguired. I use a EDS Leekseeker that uses tones and leds not a digital readout. I measures ..000,001 of a ohm that can pinpoint. The short.

Desoldering and Resoldering is very time consuming raising the repair rate too high. Excessive soldering on board also increases chance of damaging a trace run

[shortchange]

Re: the best way to find short circuit?

I have been using this method for many years now.
While other techs lug their power supply around and other expensive misleading -time consuming methods.

Chilling spray does not need a schematic or data sheet.

A EDS Leakseeker may help below. Sound expensive compared to a can of chilling spray.
Still i would like to know how much EDS Leakseeker is.

After probing around 10 parts you notice a dip on the EDS Leakseeker.
So you remove a 100 pin SMD ic to find that was not shorted
but next to the 100 pin SMD IC is a SMD cap that is bad.

You would see a large change in the ohm meter chilling the cap and no change at the ic!

An analogue ohm meter would show this CHANGE (0.1 to 10 ohms or more).

[tom66]

Re: the best way to find short circuit?

Not all shorts are temperature dependent though.

[shortchange]

Re: the best way to find short circuit?

Not all people can say they have been using this method for many years.

When I come upon a short circuit that does not change the ohm meter reading I have concluded I have NOT chilled the shorted components (parts) yet.

Each part on the the shorted power supply live will change -excuse me... have changed in ohms without looking up a schematic or data sheet to find the parts B+ connection.

[tom66]

Re: the best way to find short circuit?

I've had MOSFETs which hit 0.00 ohms shorted. And MLCC ceramic caps. If they do change, then the change will be essentially unmeasurable. It might work for smaller SMD devices, but certainly won't detect all shorts. And may also fool the high current + freeze spray method. Leekseeker is a good device.

[shortchange]

Re: the best way to find short circuit?

I have been using this method for many years.
It does work.
It has NOT been "essentially unmeasurable"
It is NOT a "high current + freeze spray method"

A change in an ohm meter connected to a short circuit has shown a change when chilled with chilling spray.

EDS Leakseeker seems more expensive compared to a can of chilling spray.
Yes EDS Leakseeker may help but not as reliable as monitoring a change in an ohm meter and some chilling spray.

EDS Leakseeker can not say a 100 pin SMD ic is shorted
or SMD cap that is bad next to it.

No schematic or data sheet needed.

[tom66]

Re: the best way to find short circuit?

I was saying my method, with freeze spray and current, may not always work with dead shorted components.

I am having difficulty seeing how a component which has a dead short (say due to catastrophic failure where the PN junction in a diode forms metal contamination, joining the two junctions and shorting the diode dead) will be temperature dependent. If the short is leaky (like 1~10 ohms) I could see it but not <0.05 ohms.

Whenever tracing a dead (<0.05ohm) short where small SMD caps are involved I would "always" suspect the caps. The transistors in your average IC have an on-resistance of hundreds of ohms, so a typical shorted 100 pin IC will -not- read 0 ohms, it'll read 10 ohms or above. There high current+freeze spray or ohmmeter+freeze spray will both work. The only major exception is ICs with power electronics in them - such as integrated DC-DC converter. Those can have very low resistance transistors in them, which makes tracing faults difficult. Luckily, in many cases, the IC will fail in multiple places due to catastrophic internal heating and over-stress. So you can test on, say, the Vcc pin of a switcher, rather than the high-current SW node.

[shortchange]

Re: the best way to find short circuit?

Your method, with freeze spray and current, was that with an external power supply?
And did you use thd ammeter built into the power supply?

Thank you for time.
Nice to see someone who understands all of this!

[tom66]

Re: the best way to find short circuit?

I just limit the power supply so the current is around 2 or 3 amps and see what melts first.

[shortchange]

Re: the best way to find short circuit?

Are you being funny?
Some of this stuff can blow up into our eyes.

[senz_90]

Re: the best way to find short circuit?

well
this is just forum for giving and accept advice,, dont be too serious for arguement it makes us to said the others way is bad. i just wanna know the best idea.. we can share together what is the best...i would test both of your method and decide what is the best method for me and the further...

[tom66]

Re: the best way to find short circuit?

Are you being funny?
Some of this stuff can blow up into our eyes.

Freeze spray melts, not the components, if you do it right. Brief, less than a second. It will not blow up if you are careful. 3 amps, from a constant-current power supply (which limits the current when driving a short) isn't going to damage anything that isn't already bad. Of course, if you connect the short to a car battery, for example, then bad things will happen.

See how I did it for a dead-short IC here
https://www.youtube.com/watch?v=7Xz-iSaEAb8&t=3m05s

[tomodachi]

Re: the best way to find short circuit?

High current from constant current power supply plus freeze spray.

Ok good idea but, freeze spray is conductive ( I guess) and may cause other short am I right ?

[tom66]

Re: the best way to find short circuit?

Not really, when you're tracing a short around 0 ohms a few kohm freeze spray doesn't matter and the liquid portion usually evaporates quickly.

[senz_90]

Re: the best way to find short circuit?

Not really, when you're tracing a short around 0 ohms a few kohm freeze spray doesn't matter and the liquid portion usually evaporates quickly.

instead of using freeze spray, it does any other option?

[tom66]

Re: the best way to find short circuit?

Canned air, when inverted, produces freeze spray.

[senz_90]

Re: the best way to find short circuit?

hey. i just realize this post https://www.badcaps.net/forum/showth...+design&page=4 maybe u have ever look before because you were discussing it too.

the schematic on the post #76. it could measure a short circuit well.. it has a really low esr measurement linear scale, it could functionally both measure low esr and short circuit i thought.. i have to translate it !! the best resolutions analog esr meter that i've ever looked !!

[tom66]

Re: the best way to find short circuit?

That can work, but remember to account for the resistance of your probes. That will add at least 0.2 ohms to the measurement which will mean small changes won't show up so well.