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Freezing or heating up components , Transistors and FETS . etc. for troubleshooting

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When troubleshooting intermittent components or failures by using freezing sprays or heating them up how do you know which component is bad when you freeze or heat up the Transistors or FET one by one but each one with drift in voltage up or down when its cold or hot , that doesn't mean its BAD

When I freeze or heat up a transistor , the voltage of the transistor or output of that stage will drift up or down , so how do I know if its bad or good?

When a transistor is an amplifier it will drift the voltage up or down when you freeze or heat it up, does this mean its bad or good?

When a transistor is a switch , it will drift the voltage up or down when you freeze or heat it up , does this mean its bad or good?

When resistors are temp failure, the resistance changes up or down depending on the freezing or heating it up

At work i had to do freezing spray and heating up these OP AMPS that were in the shape of a metal can transistor looking types like a IC chip package type, I had to freeze spray and heat them up ONE by ONE

But I can't tell if the transistor or these Op amps are good because the voltage will go up or down
 
Hello,

This kind of test is usually used when a component is already bad and the product under test shows signs of intermediate failure to begin with. By freezing the component the product begins working more normally again, hence you can start to suspect the part that was cooled.

This is a little more varied than that however because some circuits are made such that several parts are assumed to heat up normally during the start up period, and thus cooling one part alone makes it drift even though there is nothing wrong with it. If you heated or cooled them all it should drift less, if it was designed for those temperatures in the first place.

Resistors can be tested by heating or cooling but they should be tested under a more controlled environment. It's hard to determine what the real temperature of a part is when it is hit with some freeze spray for a second or two...was it cooled down to 20 deg C, 10 deg C, or 0 deg C ? We cant be sure. But if it is placed into a controlled environment like a refrigerator or freezer, we can then check the resistance and see if it remained within the manufacturer's tolerance spec. Insert it into a small oven (you can build yourself with light bulbs and a cardboard box) and you can test it for defects when it is heated up to some reasonable temperature.
 
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Freeze spray is best used to find intermittent or (cold solder joints especially with components with leads). Cold can also show defects on the board visually rather than electrically.
 
I used a freeze spray that was -40C , -40F , and spray each transistor and Op amp , it they drifted up or down way more than 10mV

How far can they drift up or down before you know the transistor or Op-amp is bad?

Freeze spray is best used to find intermittent or (cold solder joints especially with components with leads). Cold can also show defects on the board visually rather than electrically.

How do you find a Cold solder joint by using the freeze spray? I have sprayed solder joints and how do you know if the solder joint is a cold solder joint?
 
What is a GOOD drift and what is a Bad drift?

Is -40c/-40F freeze spray to strong? will it damage the transistors and op amps metal can type package?
 
As noted, freeze spraying is typically used to find intermittent failures where the circuit has a significant and sudden change in it's operation. It's not used to determine drift effects, since that requires a more controlled temperature environment.

There's no absolute answer as to whether the drift is GOOD or BAD. It depends upon the circuit.

The freeze spray should not damage good components. If they fail after spraying then they were likely marginal to begin with.
 
i'm freeze spraying an intermittent board, one component at a time

when do u use the heater on ccompontents? When a circuit is? Intermittent or other?
 
Once i freeze spray a component it will drift the voltage up or down in the volts , how do u know if the is good or bad?
 
Once i freeze spray a component it will drift the voltage up or down in the volts , how do u know if the is good or bad?
You don't.
 
So how do you know than? what good is this freeze test?

When do you do the heater test on components?

I'm not sure when to do the freeze test VS the heat test ( heating up the component ) , When do you know which one to choose and why?
 
your measuring but really i dont think it works like that, you have a board with a sometimes fault, you plug it in and its working, so the chance's are measuring everything wont give an answer, so out with the freeze spray and spray components one by one, if your lucky you spray one and things go funny! BINGO thats probably the bad boy.
heating stuff up is for when you have equipment that starts ok but fails after say 30 mins (once everything is up to operating temperature ;)) so you plug in and go round with the heat gun and if your lucky Bingo one heats up and the circuit goes iffy. thats what i assumed it was about, i didnt think you meant to measure anything as such just try and provoke the fault when it isnt there!
couldn't you ask work to send you on a course to get some the basics of fault finding? might be useful
 
Back in the old days "plastic" transistors were famous for intermittent connections of the bond wires. The little wire that connected the chip to the pins of the transistor. They would come loose with either hot or cold. Heating and cooling would often make the intermittent connections fail open. You don't see that much now days.
Here are some pictures of bonds and their problems.

http://www.aecouncil.com/Papers/aec3.pdf
 
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