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Comparing IC?
By Jestine Yong on October 18, 2007
Yes, sometimes when an IC developed a heavy short circuit you can use a similar IC for comparison by checking the Ohms value. A shorted IC will show lots of readings in some or almost all of its leads. You may even use Huntron tracker to compare the signature of both IC.
Huntron tracker Analog Signature Waveform
From what i had gone through, i found that comparing IC is not 100 % accurate! I have confirmed many IC that was tested good (in terms of ohms value and the signature waveform) yet it still breakdown when the power is apply on the equipment. You may compare IC for testing purposes but it is not the right way to judge whether the IC is good or bad. The best is still install a new IC and power it “ON” the equipment
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Robin Cheng
April 8, 2008 at 1:09 am
Hi Jestine ,
I agree with you THAT POWER ON TEST IS BEST WAY TO JUDGE IF IC IS GOOD OR BAD because it is full operation test at its actual working environment.
In troubleshooting however, powering on can make things more complicated. If we can find the fault without applying power , wouldn't it be simpler? Here is my two cents worth! (My experience is mainly from troubleshooting digital logic circuits ).
Huntrons can compare any IC in-circuit with the power off . Do be aware of factors affecting the comparison result though.
Firstly ,when you probe a point or node in a circuit , the current will find the lowest impedance path between the two points you are probing . This is good because you can immediately know where the current is going. If both boards show the same signature , you know there is no problem ! (The current is travelling along the same path between the two points.) Its that simple ! If there is a difference , you will immediately be alerted to double check for differences eg are the IC exactly the same ? (Different manufacturers will give different signatures!) Are any components connected to that node faulty ? you begin to systematically look for the cause of the difference in signature and eliminate what is good until you find the culprit ...The bad component !...troubleshooting is all about observation skill anyway.
Huntrons give you a way to see the problem!
Secondly , and the most important , ASA (Analog Signature Analysis ) which is what huntrons display is not a functional test of the IC as such ,its an input /output check of the impedance at the IC junction or interface with its outside world . If there is really a functional failure deep in the ICs circuitry ,then ASA won't find it . Its only checking whatever is connected to its interface circuitry .
To cut a long story short , when you can see the fault without applying power to a board , it makes troubleshooting very easy . there are no signals running around to complicate things.
Huntron ASA should be the first step we take in the fault finding process.
There is a learning curve to climb ,before you can be "accurate" at troubleshooting using ASA eg knowing which ranges to select is one thing which has to be learnt for each board. Its an art based on experience not so much a science , so its very hard to teach !
(Huntron provides good guides to make it easier for new comers).
Lastly why does ASA work?
Because failures are usually low impedance paths to ground ,visible at the input/ output of ICs . Most ICs fail at the interface with the outside world , seldom deep inside , because of stress .Its a bit like humans really ! we also get mental problems when we interface with the outside world right ?