Still struggling, I have made an a raw image using FTK.
When I tried  to mount the raw image, FTK asked to format the chosen virtual disk 
Then I exported  the segmented dd4.001, 002, .... 1908 files to a single raw file still using FTK.
As bonus I got  some info of the leftover file structure after MicroSoft's failed chkdsk action:
Filename	Full Path	Size (bytes)	Created	Modified	Accessed	Is Deleted
[root]	Partition 1\NONAME [FAT32]\[root]\	262144				no
VBR	Partition 1\NONAME [FAT32]\VBR	4096				no
reserved sectors	Partition 1\NONAME [FAT32]\reserved sectors	126976				no
[unallocated space]	Partition 1\NONAME [FAT32]\[unallocated space]\	0				no
file system slack	Partition 1\NONAME [FAT32]\file system slack	188416				no
FAT1	Partition 1\NONAME [FAT32]\FAT1	45780992				no
FAT2	Partition 1\NONAME [FAT32]\FAT2	45780992				no
{	Partition 1\NONAME [FAT32]\[root]\{	4194304	1980-Jan-20 00:01:32	1980-Jan-23 00:02:04		no
0	Partition 1\NONAME [FAT32]\[root]\0	5505024	1980-Jan-13 00:01:38	1980-Feb-02 00:02:06		no
2	Partition 1\NONAME [FAT32]\[root]\2	0	N/A	N/A		no
System Volume Information	Partition 1\NONAME [FAT32]\[root]\System Volume Information\	262144	2021-Mar-22 12:53:31.300000	2021-Mar-22 12:53:32		no
FOUND.000	Partition 1\NONAME [FAT32]\[root]\FOUND.000\	524288	2021-Mar-22 14:13:10	2021-Mar-22 14:13:10		no
more in:
https://www.dropbox.com/s/ueyuea9j6bogj ... 1.csv?dl=0
Can I make use of this info?
Is it possible to change the raw image file so it wil work again?
In the mean time I will Study the TestDisk documentation for more clues
greetings
hans