itsmoked
Electrical
- Feb 18, 2005
- 19,114
I just spent a weekend troubleshooting a small production run. During testing 5 boards failed. After many hours of head scratching I got the miscreant boards running but I'm puzzled why they were acting up in the first place. I present the issue in the hopes someone savvier than I can shed some knowledge.
Here's the problematic circuit. (I did not design it!)
A: Goes to a couple of resistors that set the input's gain. Not an issue.
B: Goes to a dipswitch selecting 8 different resistors (to ground) trigger point levels. Not an issue.
C: Is the output where the anomaly is seen.
NOT THE ANOMALY looks like this:
Note: there are 2 traces the first (cause) is the input that drops a volt. The larger action (response) is what's at C.
All the boards sporting the above response worked fine as always.
[!]THE ANOMALY[/!] looks like this:
NO boards with this anomaly worked. Ultimately replacing U12 fixed all the no-op units. One had to have the U12 replaced twice to get one without the anomaly that then worked fine.
It seems to me something inside this 16V/us OPAMP was not happy. Its guts look like this:
TL072 Data Sheet
Anybody got any ideas?
Keith Cress
kcress -
Here's the problematic circuit. (I did not design it!)
A: Goes to a couple of resistors that set the input's gain. Not an issue.
B: Goes to a dipswitch selecting 8 different resistors (to ground) trigger point levels. Not an issue.
C: Is the output where the anomaly is seen.
NOT THE ANOMALY looks like this:
Note: there are 2 traces the first (cause) is the input that drops a volt. The larger action (response) is what's at C.
All the boards sporting the above response worked fine as always.
[!]THE ANOMALY[/!] looks like this:
NO boards with this anomaly worked. Ultimately replacing U12 fixed all the no-op units. One had to have the U12 replaced twice to get one without the anomaly that then worked fine.
It seems to me something inside this 16V/us OPAMP was not happy. Its guts look like this:
TL072 Data Sheet
Anybody got any ideas?
Keith Cress
kcress -
