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Old 29th January 2013, 04:30 AM   #1
Jay is offline Jay  Indonesia
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Default Weird Opamp Failure

In the last one or two months I have failed many amp projects. This is mostly related to opamp based or chip amplifiers. Simple circuits, but very frustrating in the troubleshooting.

And I'm a bit scared working with laterals right now

The failures started to happen at the same time I replaced my solder to a new one. The body of the solder was in intermittent contact with the 230V power line. Initially I allowed that for "shock therapy" but after I couldn't prevent myself from screaming, I fixed it

In the last 2 days I worked on an integrated amplifier (with 2 dual opamps). Strange issues happened. Early troubleshooting suggested that the second opamp must have one channel died. Replaced the opamp and sound came from both channels. Good.

Not really. Things were wrong. My usual troubleshooting logic couldn't solve the mystery well. I couldn't understand how with one channel input the sound came from both channels. I didn't want to sleep before I fixed that. I was confused because I didn't expect this kind of failure with opamps.

The first non-inverting input (pin#3) died, but the signal came into the second input (pin#5) generated output in both output pins (pin#1 and #7). I needed to make sure that my eyes could see everything well, then to replace the opamp. But same problem with the second opamp. Both are LF356N.

Crazy. Terrible experience. But at least I know that I was right, that I couldn't live with opamp sound, even as a buffer.

Last edited by Jay; 29th January 2013 at 04:34 AM.
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Old 29th January 2013, 04:42 AM   #2
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Jay, the LF356 is not a dual opamp, it's a single.

Data sheet here - http://www.ti.com/lit/ds/symlink/lf155.pdf
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Old 29th January 2013, 05:18 AM   #3
Jay is offline Jay  Indonesia
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Son Of A Gun!!!
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Old 29th January 2013, 05:20 AM   #4
JMFahey is offline JMFahey  Argentina
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Junk that soldering iron NOW!!
Its current leak so far has killed a couple Op Amps, next it will kill you.
No kidding.
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Old 29th January 2013, 05:26 AM   #5
Jay is offline Jay  Indonesia
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Yeah terrible product. A fake one may be. Long time ago Kenmaster and Sellery products were good enough, now like sheet.

I couldn't easily replace it because the best solder pin (yes, the pin) I can find is the small diameter one. But better solder build usually use bigger diameter solder pins.
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Old 29th January 2013, 09:00 AM   #6
Bonsai is offline Bonsai  Taiwan
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wow - that soldering iron sounds like a death trap waiting for you. follow Fahey's advice and ditch it. Better to wait until you can get a decent iron than electrocute yourself.

LF356 - LOL
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Old 29th January 2013, 10:47 AM   #7
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Bonsai View Post
LF356 - LOL
It happened that the opamps position themselves in a dedicated bag for dual opamps
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Old 29th January 2013, 03:43 PM   #8
JMFahey is offline JMFahey  Argentina
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Happens often!!!
The underpaid shop attendant pulls one from the box or drawer to show it to a customer, then replaces it in the wrong one just close to it.
Next customer gets the wrong one.
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