Galaxy S3 Camera Focus Doesn't Work

Last week my Samsung Galaxy S3 phone stopped working. The touchscreen just wouldn't respond. After following various troubleshooting steps to solve the matter to no avail I eventually performed a factory reset but this still did not solve the problem. I ended up letting it sit over the weekend while I went on vacation to allow the battery to drain fully. When I returned and recharged the phone, the touchscreen started working again. However, shortly after that my charge port stopped working. After examining the device it looks like the tab with the contacts on it inside of the USB port was actually damaged. I bought a new motherboard for my phone and replaced it. The phone now charges just fine and the touchscreen works, but now I am having problems with the camera's focus. Back before I started having problems, when I would tap the screen to focus I would see and hear the lens adjusting before it settled on the "correct" focus. Now, when I tap the screen to focus there is no visible adjustment, and it does not settle on a focused image. The autofocus process simply times out. I have switched between Autofocus mode and Macro mode but this does not make a difference. I have triple-checked all of the flex connections, made sure there is no protective film over the lens, ensured the lens assembly and motherboard were seated properly, and so on but the camera still doesn't focus. In the case that it might be a software issue I cleared the cache and data for the camera app (this is the stock camera) but again, this did not fix the problem. I am thinking it is a hardware issue and am wondering if anyone here has experience with smartphone cameras and has an idea of why the focus mechanism does not seem to be operating? I do have quite a bit of electronics experience, both design and repair, and I am mostly familiar with the construction of these Samsung phones, so I am very eager to try to fix this myself rather than sending it in for repair or buying a new phone.