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Bad op amp?
Bad op amp?
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Old 23rd December 2019, 06:39 AM   #1
jkrokenberger is offline jkrokenberger  United States
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Default Bad op amp?

How often do op amps go bad? I've got a PPI ProMOS 12 here that has extremely low output on one channel. I've removed the muting transistors and checked output at the op amp. One output is normal and the other is very low. I'm getting signal to the non-inverting input and have changed the feedback resistor's value with no change in output, still very low.
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Old 23rd December 2019, 06:58 AM   #2
jkrokenberger is offline jkrokenberger  United States
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Nevermind. I am pretty sure it's a bad input coupling cap. I'll change it out and report back.
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Old 23rd December 2019, 07:03 AM   #3
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Op amps either work or they don't. They do not set the gain.
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Old 23rd December 2019, 07:39 AM   #4
jkrokenberger is offline jkrokenberger  United States
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Bad input coupling cap. Went to Nichicon UES in 10uf value on them. Will need to tweak the feedback resistor values to get the opamp outputs perfectly equal but I put them back to original and they are close for now. Need to order J108's to reinstall.
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Old 23rd December 2019, 07:40 AM   #5
jkrokenberger is offline jkrokenberger  United States
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The only op amp in this model is used as an input buffer.
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