SHORTS, voltage across resistor converts to current

[(*steve*)]

Haven't we been here before?

Get a multimeter that can measure small fractions of an ohm (or make yourself a low-ohms adapter).

watch this:

 

[(*steve*)]

Danny, if you refuse to read more than the first line of replies I will close your threads. They are getting incredibly annoying.

 

[danny davis]

ok sorry about that

He started that you need to ZERO out your probe leads which my DVM meter doesn't have

Also he was measuring resistance down to .10ohms .03ohms which my meter can't do

So sorry I asked

 

[CocaCola]

ok sorry about that

He started that you need to ZERO out your probe leads which my DVM meter doesn't have

Also he was measuring resistance down to .10ohms .03ohms which my meter can't do

So sorry I asked

Pretty straight forward you need to invest in better testing equipment if you want to use that technique...

OR

(or make yourself a low-ohms adapter)

Never mind that wasn't the first line of the reply, you likely missed it...

 

[danny davis]

yes that is one technique

M Technique is disconnecting components that are tied to Vcc 5 volts , like pull up resistors, collector resistors, op amps pins , IC pins,

I just disconnect them one by one until it the other 3 volt rail went back to 3 volts again

Thats why i asked if you guys knew of any other techniques

 

[Rleo6965]

yes that is one technique

M Technique is disconnecting components that are tied to Vcc 5 volts , like pull up resistors, collector resistors, op amps pins , IC pins,

I just disconnect them one by one until it the other 3 volt rail went back to 3 volts again

Thats why i asked if you guys knew of any other techniques

If your troubleshooting a power supply with separate board or load. Remove connector of power supply before testing DC output. SHORT could be in your separate Load / board and not in the power supply.

 

[(*steve*)]

Have you tried googling "low ohms adapter"?

You might find something like this.

 

[danny davis]

Most of the DVM meters don't go lower than 1 ohm

This guys meter was going Point .10 ohms .18 ohms, . 03 ohms

Plus you can Zero out your probes

Cause when i zero out my probes its like 10ohms i think

I'm going to look it up low ohm adapter

 

[danny davis]

SHORT could be in your separate Load / board and not in the power supply.

Yes, that is what i always disconnect first is the power supply from the Circuit to test if the power supply has a short

That cuts the troubleshooting in HALF for me

Thats the basic rule of thumbs in troubleshooting

Thats whats i'm asking is some basic rule of thumbs for troubleshooting

 

[(*steve*)]

Most of the DVM meters don't go lower than 1 ohm

You've stopped reading past the first line again Danny.

Are you SURE your meter doesn't read under 1 ohm. Even my nasty cheapies measure down to 0.1 ohms.

Anyway, you might find reference to something you can use in one of my earlier (apparently unread) messages

 

[danny davis]

When I put the probes together
The Fluke Meter measured 0.1ohms

The Hewlett Packard meter measured 0.1139 or 0.0860

Both , you can't zero out the probes

do u guys know which meter that is cheap that you can zero out the ohms?

It look like that guy in the video had a fluke meter right?

 

[Raven Luni]

For a reading of 0 ohms try using liquid nitrogen.....

 

[(*steve*)]

When I put the probes together
The Fluke Meter measured 0.1ohms

The Hewlett Packard meter measured 0.1139 or 0.0860

Both , you can't zero out the probes

do u guys know which meter that is cheap that you can zero out the ohms?

It look like that guy in the video had a fluke meter right?

Those resistances are probably the resistance of your leads etc. It doesn't matter.

All you need to do is follow the procedure until you get the minimum resistance and you've found (or are really close to) your short.

 

[danny davis]

yes the short will match the Probe Resistance measurement

If my probes measure 0.1 ohm , the short should be close to that cause 0.1ohms is the zero reference

 

[danny davis]

I am measuring with normal probes with the DVM meter and oscilloscope

do you guys know what i can do with standard probes so I can probe SMT, SMD and fine pitch chip pins?

the probes are to big and cause shorts when i'm measuring , what can i do

I had to wrap bare wire would the probe leads put the bare wire keeps slipping and it bends where you're probing

 

[CocaCola]

do you guys know what i can do with standard probes so I can probe SMT, SMD and fine pitch chip pins?

I'm going to *SNIP* it there, PLEASE stop saying fine pitched this or that chips and what not, that generic description provides no reference point! Give a specific package and pitch , OK? I can measure a large percentage of 'fine' pitch components just fine with standard probes...

the probes are to big and cause shorts when i'm measuring , what can i do

Use a smaller probe, pay more attention or find a common point to measure from...

I had to wrap bare wire would the probe leads put the bare wire keeps slipping and it bends where you're probing

 

[danny davis]

There was a SHORT on a board today

I put the probes together and measured 0.0867, that is the zero reference point of my DVM probes together

Test Point 18 was 1.20 ohms
Test Point 25 was 1.20 ohms
R58 was 0.2058 ohms
R25 was 0.2057 ohms
R7 was 0.2478 ohms
Test Point 27 was 0.2078
R32 was 0.1803

All of these points were making continuity with the 5 volt rail

The SHORT was 0.1513 ohms with the 5 volt rail

I would think if it was a SHORT to the 5 volt rail it would be the same as the zero reference of the DVM meter which was 0.0867 ohms

But the SHORT was 0.1513 ohms not 0.0867 ohms

 

[(*steve*)]

You found it though? right?

The zero reference is really meaningless although it might be nice to have. You're looking for the minimum value. There is no reason why the short will be zero ohms -- in fact it WILL NOT be zero ohms (nothing is).

I think it is possible that you kept one meter probe on a single point on the ground trace, so the additional resistance is a combination of the resistance for the short and the resistance of the ground trace.

Congratulations, I sounds like you may be acquiring another skill. You probably need to practice a bit though.

No need to shout SHORT at me though.

 

[danny davis]

I kept one probe on the 5volts regulator output as my Reference and used the other Probe to do the resistance measurements that were only making continuity with the 5 volt rail

There is no reason why the short will be zero ohms

I always thought it was suppost to be zero ohms, thats why I was confused

 

[(*steve*)]

And you always thought a trace on a PCB was zero ohms, and the resistance of your meter probes was zero ohms.

In most cases you can assume they are, but in other cases you can't.

In this case you can use that information to help you narrow down a fault.

Even a soldered joint has a resistance. I have some 7 milliohm (0.007 ohm) current sense resistors. One major issue is that the traces leading to them and the solder joint itself can add significantly to this resistance.

You could also look up "4 wire" or "kelvin" testing of resistance. The aim of that is to minimise the effect of resistance in the probe leads

edit: I think I've also said multiple times that a short is not necessarily zero ohms. Imagine if instead of a 0.1uF capacitor across your power supply you soldered in a 0.2 ohm resistor. That would probably short out your power supply, but it is much higher than zero ohms.