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Testing IC chips,,,,


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6/17/1999 7:51 PM
David Manson
 Testing IC chips,,,,
I'd like to know the basics on testing IC/opamps to see if they are bad...  
 
 
 
thanks..
  
6/17/1999 8:29 PM
anonymous Re: Testing IC chips (R.G.)
The basics for opamps are  
 
1. verify that the power to the IC is good AT THE POWER PINS OF THE CHIP  
 
2. For opamps that are used as linear amplifiers - that is, not in LFO oscillators or as comparators - the voltage at the inverting (-) input and the output must follow the voltage at the noninverting input for no-signal conditions. If the (+) input is biased at, say 4Vdc in a 9V circuit, the (-) input and output can be no more than about +/-10mv different from that; if they are, the amp is toast.  
 
3. The bias voltage at both the inverting and noninverting inputs must be within the "input common mode voltage range" for that specific IC. New rail to rail and single supply opamps have CMR's that include the negative supply and close to the positive supply. Older opamps like the 741, TL07x, and so on may be limited to staying at least 2V away from the supplies. When you get the inputs too close, the outputs go non-linear.
  
6/28/1999 10:26 AM
paul perry
RG's advice is good (as always). Anyone wanting a comprehensive troubleshooting guide, get "Troubleshooting Analog Circuits" by Robert A. Pease. He's even older than me, and this book has saved my ass dozens of times. Hell, he actually DESIGNED lots of the chips in our stomp boxes! Lots of advice on tools, caps , everything.
  
6/28/1999 12:36 PM
R.G.
ABSOLUTELY CORRECT!!!!
  

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