DKjr Missing Sprites and upside down

mikes arcade has repair logs on dkjr. you probably also have a bad logic chip near the multiplexer that is stuck flipping the video

look at bottom of drawing 4 ok dkjr schematics at the flip input and follow the path to see which chip in the chain goes bad


Problem: Missing sprites.

Tools: Logic Comparator (BugTrap) and Logic Probe

There were NO sprites at all on the game, it would play fine, but it's no fun to try and guess where Junior is and where the bad guys are. This one I found with a logic comparator (BugTrap). There was a an LS86 at 3D that has some type of gunk on it so I used my logic comparator on it. It was fine! Just for grins, I checked all the LS86s on the board to try an shed some light on the problem, they were all working as they should. Next I looked with my logic probe at the pins on the first LS86 to see if the inputs were pulsing. Nothing, they were dead! So, looking at the schematics, I found the LS86 was fed by the counter at 3E. Again using the logic comparator, I plopped in a good LS163 and clipped on to 3E. When I powered the board, all the lights on the comparator lit up. If there is a mismatch on an input or output between the chip on the board and the chip in the BugTrap the light for that pin will light up. I reset the LC (Logic Comparator) and only the output lights lit up. Found a bad LS163 it appears. I tried piggy backing the chip and it changed nothing. :-( So I socketed the chip and plopped in my known good one. Woohoo! All the sprites came back! So it looks like I've finally found a cure for those missing sprites. :)

Just for fun I socketed the LS163 next to it at 3E and put the bad chip in, just to see the results. It was the same, so if either of them are bad, no sprites. NOTE: These chips are responsible for the Horizontal position of the sprites on the screen.

Solution: Replaced bad 74LS163 at 3D.
 
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