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Old 12th February 2013, 08:50 PM   #1
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Location: Groningen
Default Quick (faulty?) op amp question

I'v been tinkering woth op amps for some time now. I think I've got the basics down .
For some unknown reason, a previously perfectly fine DIY circuit (FX loop signal fase toggle) stopped working. I soon realised there was DC on the output. Turned out to be full Vcc. The three other parts of the TL074 are fine. I checked and re-checked everything, but all seems surrounding circuitry seems fine. Do I need new glasses, or is this a way an op amp can fail??
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Old 12th February 2013, 08:56 PM   #2
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Location: Fosser, Aurskog-Holand, Akershus, Norway.
This is one of the ways an OP-amp can fail.

Often also external cirquits need to be controlled for any failure.
If possible, detach any output device at the faulty output of the OP-amp, and try again to power up. If the output of the OP-amp still is at full VCC, you may try to just replace the TL074.
Sooner or later you end up with TANDBERG
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Old 12th February 2013, 09:06 PM   #3
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Thanks. I thought I was going nuts.
It still in the 'bread board' stage, so no harm done to Amy existentie equipement. Is there any reason an op amp woud fail this way?
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Old 12th February 2013, 10:58 PM   #4
Enzo is offline Enzo  United States
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Location: Lansing, Michigan
There is always a reason, but you may never know it. All it takes is a slip of your meter probe, which you may not realize you did. breadboarding generally means a lot of handling of parts, so a static discharge into the part may have happened from your fingters. Oh so many things it could be. There is also something we call random component failure. You may have compromised the part somehow a week ago, and it jut now got around to finally failing. Sometimes ther is an A caused B moment, but most times, it happens and the exact reason is forever a mystery.

When I have an amp with an op amp signal path, and it is not passing signal, in fact the first thing I do is verify the power supply is working then go down the row looking for DC on the output pins.
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