First symptoms were no video signals (no sync) but sound worked: replaced 74LS74 @ M9.
Then black screen with sound: replaced 2 * 153s @ D2 & E2.
I obtained an image but with a corrupted sprite layer (completely covering the background layer):
I replaced 2 RAMs @ B11 & D10:
I finally noticed dipswitches 1 were not working: replaced 74LS245 @ M2.