Ok some testing was done though not by me, but someone experienced with these clocks that asked me to post this to help the community.
These are the test results:
1. Tried both B237 and B134 - IMG & IMGC File type did not matter, both worked
2. Tried in 4 different Run-DMD clocks (Classic with updated firmware and Exp-one, Pinball MK2, Pinball Original, White) - The above file types worked on all these boards.
3. Did all of these tests on both software - Etcher and HDDRawCopy1.10Portable - This did not matter but HDDRawCopy was way faster.
5. Tried a bunch of cards - This appears to be the problem when it doesn't work.
6. In most cases where it worked I had to hold the "3" button to put the controller into setup mode. IF the display goes into the slow blink mode the card will likely work but you have to wait 20 seconds or more to get anything to display. IF it's a normal blink the card will likely not work.
Here's a summary of the cards that worked.
1. 8GB Kingston MicroSD
2. 16GB Microcenter MicroSD (US PC Store)
3. 32GB SanDisk MicroSD
4. 32GB Kingston MicroSD
5. 32GB Kingston SD - I had 2 of these. They came with recent Run-DMD boards.
The following cards did not work.
1. 2GB Transend SD - Note that B237 is too large for a 2GB card.
2. 4GB Transend SD - I had 2 of these - Neither worked.
3. 8GB Transend SD - I had 4 of these - None worked.
4. 16GB Microcenter MicroSD - I had 3 of these including the one that worked above. They appear to be identical.
Conclusion
It may be worthwhile to try each of the cards that you have until you find one that works. If buying a new card a newish Kingston 32GB card seems to be the most likely to work. Fortunately these aren't expensive but may take some trial and error to find one that works. Odds are very high that other cards will work though.
In Summary
Both files work on most dmd clock boards but the weakness is the SD card brand and memory size.
Hope this helps
Jady / Swinks and friend