Hugo Holden
Veteran Member
Neither have I. And that leaves one feeling a little uncomfortable.I have never come across a fault like this myself.
Dave
I would have put my money on something external to the IC, such as a Tin whisker bridging pin 1 & 2. If that was the case then the de-soldering in the area would have destroyed it it. We can only rely that he checked this properly as he was asked to do.
There are two methods that could help verify what went wrong:
The removed IC though could be placed on a breadboard with a 5V supply and examined, to try to determine what went wrong with it. Its current drain and logic functions & input currents are easily checked. If on testing, that removed IC turned out to be normal, then it could have been a whisker.
The other method (fault replication), in this case, is after the new IC is fitted, is to; 1) short pin 1 & 2 together as an experiment and 2) try disconnecting pin 14 to see if either of those two things duplicates the fault visible on pin 9 of U2.
Of course once most people find an apparently faulty part and cure it with a new part, they don't often have the inclination to find out exactly why the original part gave trouble and the old part just goes in the bin. But I'm sure if we were doing this repair on our own computer, we would have to know what happened, especially in an unusual case.