My UKRAA PicoMuon detector stopped saving CSV data files on to the 64GB SD card plugged into it.
I realised the SD needed to be re-formatted. The PicoMuon requires the format to be FAT32, and NOT exFAT or NFTS. Windows would not do this formatting as card > 32 GB.
So I decided to use GUIFormat to format the disc. I got this software from Nero mirror at https://get.nero.com/publishers/Ridgecrop/guiformat/guiformat.html
Also available at:
https://www.astronomy.me.uk/wp-content/uploads/2026/07/GUIFormat_NeroGet_0355920260421.zip
In this case, even that would not format the SD card. This can happen if the SD card’s partition table has become corrupted or Windows Disk Management is getting confused.
In fact, in my case, I looked at the SD card in Windows disc Management (part of Computer Management) and found that somehow there were two partitions on the SD card = 2 volumes. I deleted both volumes to give one single unallocated space.
Following this, GUIFormat could not not see the card at all – just didn’t appear – and Windows computer management could not create a new simple volume on the card.
I ran these commands:
I used DiskPart:
Opened Command Prompt as Administrator.
Typed:
diskpart
Then:
list disk
Found which disc was the SD csrd – pretty easy on basis of size. Mine was disc 2.
As long as the SD card appears in the list, then it means Windows can still see it, which is the important bit.
Now I fully reset it and rebuilt the partition cleanly using DiskPart.
⚠️ Be very careful: make sure Disk 2 really is the SD card (correct size). Everything on it will be erased.
Step-by-step fix
In the same Administrator Command Prompt:
diskpart
select disk 2
clean
create partition primary
format fs=fat32 quick
assign
exit
What this does
clean → wipes broken partition structure (fixes most “can’t create volume” issues)
create partition primary → makes a fresh usable partition
format fs=fat32 quick → formats it for the PicoMuon detector
assign → gives it a drive letter.
I got as far as format part above then the process failed. If FAT32 fails on format, then it usually means the card is >32 GB (mine was 64GB).
So I moved over to GUIFormat and tried to format it as FAT32.
However, GUIFormat would not still recognize the card even though in Windows Disc Management Utility (within Computer Management), the card appeared. So, in disc management, I formatted as NTFS first. Now GUIFormat could see the card and I could format as FAT32.
Success!
After all of the above, once inserted in the PicoMuon, the PicoMuon was now able to start creating CSV data files on the SD card again.
in case this happens again, I think I should replace the 64GB SD card currently in the PicoMuon with a 32GB SD card.
I have just ordered two 32GB SD cards (good make = Sandisk). Both I will format as FAT32 and I will use one now in the PicoMuon and keep a spare available in case I suffer failure again.
Andrew