MacOSX Fix damaged partition map

Solution 1:

The output you have posted does not indicate any problems with the partition map. The output does indicate the drive is in the wrong USB drive enclosure. The drive has a 512 byte sector size and the USB enclosure is silently converting 512 byte sectors to 4096 byte sectors. Your best option here is to find an enclosure that does not do this conversion. Otherwise, proceed as follows.

Note: The OP indicated in a comment that the problem was solved by changing enclosures. Therefore, the answer below was never used.

Below is what the output from gpt -r show disk0 looked like when the drive was being used by the now fried the machine.

    start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640 1953115488      2  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
 1953525128          7         
 1953525135         32         Sec GPT table
 1953525167          1         Sec GPT header

The two partition entries shown in the above table can be converted from a 512 byte sector size to a 4096 byte sector size by dividing by 8. The result is shown below.

          5      51200      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      51205  244139436      2  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC

If you create a new empty GPT, then output from gpt -r show disk3 will look like the following.

      start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2          4         Pri GPT table
          6  244190635
  244190641          4         Sec GPT table
  244190645          1         Sec GPT header

At this point two problems are revealed:

• Creating a new empty GPT will overwrite the first 4096 byte sector of the first partition on the drive. This would be the FAT32 formatted EFI partition.

• The size in 4096 bytes sectors of EFI partition is 51200. This is below the minimum of 65527 required by the FAT32 format. This is stated in the Microsoft article UEFI/GPT-based hard drive partitions. The pertinent part is shown below.

  

So, either problem separately or together results in an unusable EFI partition. If you are only interested in mounting the APFS volume(s), then you can enter the commands given below. These commands were derived from klanomath's answer to the question How to fix Mac hard drive partition showing as FDisk_partition_scheme.

Note: You will only be adding the APFS container to the new GPT.

Below I assume your external drive is still disk3.

sudo dd if=/dev/zero bs=4096 count=6 of=/dev/disk3 
sudo gpt create /dev/disk3
sudo gpt add -b 51205 -i 1 -s 244139436 -t apfs disk3

Steps Needed to Move the EFI Partition

Note: Since the OP indicated interest in transfer information from the old HD, I only outlined the steps. I assume the OP is going to erase the entire drive once the information is transferred. If so, then the OP can ignore this section.

These steps leave the EFI partition at the end of the drive. When testing formatting operations which require an EFI partition, macOS seems to accept an EFI partition that is not at the beginning of the drive.

1. Use the Disk Utility to create a sparse disk image of a large enough drive so a EFI partition would be automatically created.
2. Use the dd command to copy the EFI partition from the external drive to EFI partition in the disk image.
3. Create the empty GPT, then add the APFS partition.
4. Use the diskutil command to shrink the APFS partition by at least 300 MiB.
5. Use the gpt command to create a 300 MiB EFI partition below the APFS partition.
6. Use the newfs_msdos to FAT32 format the new EFI partition with the volume label EFI.
7. Mount both EFI partitions and use the Finder to copy the contents from EFI partition on the disk image to the EFI partition on the external drive.
8. Unmount both EFI partitions, then eject the disk image and place sparse disk image file in the trash.

Other References

USB adapters silently change sector size