Even though the Logic Board & GPU were previously replaced you could still have a bad GPU on this board.
You can try forcing the laptop to use the Intel GPU by using gfxCardStatus.
https://github.com/steveschow/gfxCardStatus/releases/tag/v2.4.4i
If you cannot boot normally to install gfxCardStatus, then check out these links for alternative methods of forcing the laptop to use the Intel GPU:
http://dosdude1.com/gpudisable
See the latest news section of this link:
https://github.com/steveschow/gfxCardStatus
There is also a chance you could have a failing hard drive. If you cannot boot into macOS to use DriveDx, then using another computer you can create a bootable Knoppix Linux USB drive which can be used to check the health of the hard drive. Use the downloaded Knoppix .iso file as a source for Etcher (Mac/Windows/Linux). Option Boot the Knoppix USB drive and select the orange icon labeled "EFI". While Knoppix is booting the computer may appear frozen on the boot picker menu so give Knoppix lots of time to finish booting.
If Knoppix boots to a desktop, then click on the "Start" menu icon on the lower left corner of the Taskbar and navigate the menus to "System Tools ---> GSmartControl". Within the GSmartControl app double-click on the laptop's hard drive to access the drive's health information. Post the complete report here.
If Knoppix only boots to a black screen with white text and a command prompt, then it may mean the GPU is faulty. If you use the following command it will access the health information on the laptop's hard drive (assuming only one drive is installed or connected to the laptop):
sudo smartctl -a /dev/disk0 | less
Use the up & down arrow keys or the Trackpad/mouse wheel to scroll up & down the health report. Take pictures of the report and post them here. Pressing "q" will exit the health report and return you to the command prompt where you can issue the shutdown command or just hold the power button to turn off the laptop:
sudo shutdown -h now