AIO input 8 stuck on

[telewizard13]

I decided to dig into this problem a bit more and I think I found and resolved the issue. It appears to have been the faulty soldering of U35. FYI, I was Director of Engineering for CBS Television in Baltimore Maryland USA for 29 years before I retired in 2017 (I still work there part-time.)  I have been an EE working in broadcast engineering since the 1970's. I downloaded and studied the pdf of the AIO board's schematic, and took the metal cover off of the board. I have an extensive electronics lab and test equipment in my home, so I first traced input 8 from the connector to its opto-isolator and then to IC U35. I decided to check for possible thermal or mechanical connection problems with the related input ICs. I put some isopropyl alcohol onto a Q-tip and first touched the input 8 opto to cool it, and there was no change in status. However, when I ever so lightly touched the Q-tip to the top of IC U35, input 8 instantly returned to the OFF state for a few seconds, then it failed ON again. I repeated the test again with the same result. Looking at U35 under a microscope, I saw that some of the board pads and IC pins barely had any solder on them. Since I own a SMD hot air rework station, I put some flux on the IC's pins and reflowed the IC to the circuit board pads. I powered up the board again to test it, and I could not get it to fail again, so reflowing U35 appears to have fixed the problem. To make sure all the IC pin connections were well established, I added a small amount of Chip-Quik solder paste to the IC pins and reflowed it again with hot air. I checked it again under the microscope to make sure there were no solder bridges between the pins. I then re-powered the board and monitored input 8 while I heated and cooled the IC several times with a heat gun and alcohol, and board seems to be totally stable and working normally now. I'll monitor it for a few days to make sure it stays fixed, and will let you know if I have any further issues.
Regards,
Telewizard13