SHORTS, voltage across resistor converts to current

[CocaCola]

WRONG. You have failed to notice that car was 3.64 metres in length and thus the answers are out by a small factor that involves the speed of light in an imperial universe.

Darn, always those little details...

 

[Rleo6965]

What happened here? So many negative numbers and blood.

 

[(*steve*)]

Danny, in case you've given up, the answer to Questions 4 and 5 are (in no particular order) 9V and 0V. Can you figure out which answer goes with which question? The switch acts as a short when it is closed.

 

[danny davis]

If Vcc to Ground Is Shorted, How do I find which stage is causing the SHORT to Vcc To Ground?

 

[CocaCola]

Danny, in case you've given up, the answer to Questions 4 and 5 are (in no particular order) 9V and 0V. Can you figure out which answer goes with which question? The switch acts as a short when it is closed.

Here it is simulated

http://www.falstad.com/circuit/#%24+13+5.0E-6+10.20027730826997+50+5.0+43%0Aw+192+352+464+352+0%0Av+192+352+192+192+0+0+40.0+9.0+0.0+0.0+0.5%0Ag+192+352+192+416+0%0Ar+464+352+464+192+0+3141.5899999999997%0As+192+192+336+192+0+1+false%0Aw+464+192+336+192+0%0Aw+192+128+192+192+0%0Aw+464+128+464+192+0%0Aw+192+128+240+128+0%0Aw+416+128+464+128+0%0Ap+240+128+416+128+0%0A

Cut and paste

 

[CocaCola]

If Vcc to Ground Is Shorted, How do I find which stage is causing the SHORT to Vcc To Ground?

You follow Vcc and Gnd until you find it...

 

[danny davis]

To Find a short from Vcc to ground, you have to turn the power OFF?
And use a DVM ohm meter to measure if there is zero ohms at any stage of the circuit?

If the Vcc to Ground Are Rails or Bussed, If i put a ohm meter across the Vcc to ground anywhere in the circuit or stage it will measure zero ohms if there is a short

How do I know which stage of the circuit is the faulty stage that is causing Vcc to ground short?

Do I have to Disconnect each stage of the circuit one by one from Vcc?

 

[(*steve*)]

If Vcc to Ground Is Shorted, How do I find which stage is causing the SHORT to Vcc To Ground?

OK, here is one way that will work if there is a dead short between Vcc and gnd.

1) Turn off the power

2) measure the resistance between Vcc and Gnd on a multimeter that measures low ohms (say milliohm resolution).

3) move the probe along the gnd and/or vcc tracks until the resistance reaches a minimum value. At this point, chances are that you have the probes close together (and the short is a bridge of some sort between them) or at either end of a component (that is shorted).

This technique will not work (or will be much harder) if you don't have a suitable meter, if the short is not very close to zero ohms (e.g. 10 ohms, or a diode junction to ground), or if you have a board with internal ground and power layers (in general it's likely not to work with a board that has > 2 layers, and can be a pain if the board is double sided and the power/ground snake their way from side to side of the board)

 

[CocaCola]

To Find a short from Vcc to ground, you have to turn the power OFF?

I generally do it with power off and my eyeballs...

And use a DVM ohm meter to measure if there is zero ohms at any stage of the circuit?

That might work...

If the Vcc to Ground Are Rails or Bussed, If i put a ohm meter across the Vcc to ground anywhere in the circuit or stage it will measure zero ohms if there is a short

Only if it's a zero Ω short...

How do I know which stage of the circuit is the faulty stage that is causing Vcc to ground short?

Steve has told you many times, learn you circuit... Look for the short, take educated guesses based on what the circuit isn't or is doing... Take measurements that might give you a clue as to the location or at least area of the short...

Do I have to Disconnect each stage of the circuit one by one from Vcc?

I would say no, but it might help in certain instances... As Steve (and others) keep telling you, your answers are circuit dependent... What works on one circuit might not work on the other...

The "this is the way to do it" answer you are looking for simply doesn't exist, yo have to owe up to this or else we will continue to go in circles...

It's become more and more clear that you lack even the most basic understanding of electronics,let along electronics repair... Yet you continue to argue with those that do know, you play the role of the student but argue back when you don't like the answers the teachers give you...

Steve pointed out with his little lesson that you don't have even the basics down, I will admit when first when he posted it I thought it was a trick and wondered why he posted such a basic set of questions that are obvious (that is why I simulated it to make sure I wasn't missing something obvious due to a brain fart), but it proved his point and should have driven something home with you...

 

[danny davis]

move the probe along the gnd and/or vcc tracks until the resistance reaches a minimum value

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

Cause If I take my probes and measure the Vcc to ground for each stage , won't they measure zero resistance because its a Dead short from Vcc to ground?

 

[(*steve*)]

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

Cause If I take my probes and measure the Vcc to ground for each stage , won't they measure zero resistance because its a Dead short from Vcc to ground?

This is why I didn't mention this earlier.

You have a fundamental ignorance of basic electronics.

1) What is the resistance of a piece of wire? Is it zero? Or is it close to zero?

2) What is the resistance of a track on a PCB? Is it zero? Or is it close to zero?

3) What is the resistance of a dead short? Is it zero? Or is it close to zero?

Bonus marks...

4) What is the resistance of a soldered joint? Is it zero? Is it close to zero?

(Hint: *nothing* you're likely to come across has a resistance of zero ohms)

So... If you have a short somewhere between two traces on a PCB, what happens as you move the probes close and closer to the short?

 

[CocaCola]

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

Cause If I take my probes and measure the Vcc to ground for each stage , won't they measure zero resistance because its a Dead short from Vcc to ground?

Build the attached circuit, the 51K value can be anything you desire... FYI those black things are diodes

Give me the resistance across the rail side (point A & B) and then give me the resistance across the stage one side (point C & D)...

Now the bonus round question...

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

 

[danny davis]

Give me the resistance across the rail side (point A & B)

Zero Ohms

and then give me the resistance across the stage one side (point C & D).]

Zero Ohms?

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

YES?

 

[danny davis]

IF the circuit is working good the lamp should lite up normal?

If there is a SHORT in the power supply or a stage in the circuit the Lamp should lite up very bright?

If the LAMP is very bright then the circuit or power supply have a SHORT somewhere.
The Next step is to disconnect the power supply from the PCB circuit stages.
Now check if the LAMP is still Brighter
IF the Lamp is still fully bright, then its a component in the power supply
If the Lamp Is not bright , its a component in a stage of the circuit on the PCB.

Now with the lamp fully bright you know there is a SHORT somewhere on the PCB in one of the stages, by removing transistors or FETS one by one until the LAMP Light Dims back to normal you have found your SHORT component right?


what kind of LAMP can i use to measure the current of the power supply?

The Circuit is between 3 to 5 volts

Can I put any kind of 3 to 5 volt lamp?

 

[danny davis]

A SERIES LAMP to measure the Current of the PCB and power supply

 

[CocaCola]

Zero Ohms



Zero Ohms?

If there is a DEAD SHORT from Vcc to ground, won't all the stages measure zero resistance?

YES?

As expected, you don't even have clue about the most basic of basics... Do you even know how diodes work?



Right
Wrong
Wrong

Did you build it and test it like I asked? Not hard to guess the answer to that is, no...

 

[danny davis]

Right
Wrong
Wrong

Are you sure? I would think the zero ohms short would TAKE OVER since its the least path for current

So ONLY the faulty stage will measure zero ohms?

 

[CocaCola]

Are you sure? I would think the zero ohms short would TAKE OVER since its the least path for current

So ONLY the faulty stage will measure zero ohms?

I'm positive, it's clear you don't have a clue as to the most basics...

Build it and test it...

 

[danny davis]

wouldn't a SERIES LAMP help me find the SHORT?

Because the short is some component on the PCB or power supply

What kind of lamp should i get?

 

[CocaCola]

Are you sure? I would think the zero ohms short would TAKE OVER since its the least path for current

Do diodes have a forward biased they have to overcome before they pass any negligible current? What happens bellow that threshold?

Hopefully you starting to see that there is not always that black and white answer to the questions you seek...