I recently bought Ghouls'n Ghosts US older revision (with PPU soldered on B-board) with Gfx background issue (wrong colors in attract mode, lots of zeros on the background in game...) for a cheap price, thinking it was a dead PPU.
Pic of the board :
Things I did :
1/ I swapped the A-board with another one : A-board is fully working.
2/ I checked if there were cut tracks on the B-board : no cut tracks.
3/ I launched the Test mode to check the colors, they are all OK.
4/ I replaced B-board game pal (DM620) with a gal I did, the issue is still there, the pal is OK.
5/ I dumped and checked all Gfx roms + program roms, they are all OK.
6/ I checked all the TTL (LS245, LS08 and LS04) and all the network resistance on the B-board : all seem OK.
Things to do :
1/ To swap B01 PPU with a B21 one.
2/ To be able to dump SMD HN62404FP Gfx and program roms (4 Gfx roms + 1 program rom).
I did a small vid, let me know if you think it could be another thing that PPU issue or a bad SMD :