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Repair Logs

Donkey Kong Junior (Nintendo) PCB repairs

A common problem I see with both DK and DKJr boards, that I have not seen covered anywhere, are occasional vertical bar of garbage. This garbage vertical line can be anywhere through or near a sprite and is usually the full height of the sprite it appears with. These glitches appear, then go away as the sprite moves across the screen. I've never been able to pinpoint what causes these graphics glitches. But Id' sure like to find out. It is not a typical 7x eprom problem. Here is an example picture of what I'm referring to. If you've run across a problem like this and found the cure, I'd like to hear about it. Thanks!


Problem: resets constantly, will not boot

Solution: replace bad 2114 RAM at 4C on the CPU board.


Problem: game plays but numbers instead of graphics fill the screen

Solution: replace bad 2114 RAM at 2P on the video board.


Problem: scratchy intro tune, music missing during game play.

Solution: replace bad LM324N at 7K on the CPU board.


Problem: All sounds are present, but very low volume.

This board took a hit from the monitor sound amp being hooked up backwards 1. The large 3 pin connectors were put on incorrectly. When the game was powered on, the board smoked about 5 parts, R1, R38, R28, R29, C12 and Q1. The most of them actually flamed and all were toasted. Also the traces under R29 and R29 were burned, as well as the pads that R1 were soldered to were destroyed. After fixing all those parts, the sound was still faint.

Solution: R1, R38, R28, R29, C12 and Q1 and repaired many toasted traces

1This also tends to knock out the green from the display. See the next log entry for details.


Problem: Green color absent from the display.

This seems to be a common occurrence if the problem above has occurred.

Solution: replace bad transistor Q14, emitter was stuck low.


Problem: Jump sound way strange.

Wiggling the cap at C24 would change the pitch of the jump sound.

Solution: replace bad C24 - 47uF @ 16V electrolytic cap.


Problem: Jump sound missing.

Solution: bad cap C15, 22 uF @ 16V Tantalum capacitor.


Problem: Game won't coin.

Solution: 2 fried resistors, R54 and R55, bad cap C38, 10 uF @ 16V Tantalum capacitor.


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.


Problem: Sparklies or Graphic glitches.

This is a pretty common problem on DKjr and DK boards, but this is the first time I've found a cure.

This particular board was fine until I let it run about 1/2 hour. I had upgraded it to DDK and when testing it as a Jr board saw no problems, but didn't' let it run too long before I upgraded it.

After the upgrade, I let it sit and burn-in while I went to eat dinner. When I came back, the top or the screen above Polly screaming help in DK was filled with glitches! I booted over to DKJr and the key on the top exhibited the same problem with sparkly glitches. So, I grabbed a can of freeze spray. All the ECLs were really hot to the touch, so I hit them one at a time, then watched the screen. The faulty chips was a MC10124 at 4H, this chip is a quad TTL->MECL translator. The MC10125 is it's counter-part and goes from MECL->TTL.

After letting it run another 1/2 hour or so, in DK mode I noticed just a few sparklies at the top, under the high score. So I shot the MC10125 at 4F with freeze spray and watched for more sparklies. As long as I shot the chip every couple of seconds, the sparklies didn't show up. If I waited a few minutes, they would again appear. Changing both chips solved the sparkly problem with this board.

Solution: 2 bad ECL translators, an MC10124 at 4H and the MC10125 at 4F.


Problem: Game plays blind

This was a difficult one to find. I first tried various things to that had no effect. I did notice that if I shorted pins 11 & 12 on the MC10125 at 4F I would get the background only. So I fumbled along replacing all the TTL->ECL and ECL->TTL  translators. These are the 10124 and 10125 chips. This had no effect. Dummy me. I should have just checked the 10125 outs and the 10124 ins (all TTL signals). After replacing the above 4 chips, I finally did just that. I noted that I was getting TTL signals into the 10124s, but nothing out of the 10125s. There are only 2 things between these chips, the resistor packs (RM3, 4 & 5) and the ECL RAMs. I desoldered the ram at 2H and powered up the board without the chip installed. I got a picture!!! But the colors were messed up. Replacing 2H gave me a foreground and background picture with bad colors. Well, I knew I was half way home at this point. Replacing the 2nd RAM at 2E gave me a perfect picture. :)

Solution: Replace both ECL RAMS (HM10422) at 2E & 2H on the Video Board


Problem: White Playfield, no graphics

Solution: Replaced both ECL RAMS (HM10422) at 2E & 2F on the Video Board


Problem: Missing sprites, background graphics were fine

Solution: Replaced both ECL RAMS (HM10422) at 2E & 2F on the Video Board


Problem: No digital sound

Solution: Bad DAC08 (8K) and bad LM324 (7K)


Problem: Missing sprites. Had random static sprites that were wrong and no motion graphics.

Solution: Bad 74LS161 at 5K, no activity at all on the outputs.


Problem: Music constantly playing same tune.

Solution: Bad 74LS174 @ 3D


Problem: Dead board, no clock.

Solution: Bad 2SC1215 (NTE199) transistors at Q1 & Q2 on the video board


Problem: No digital sounds, analog sounds are fine

Solution: Bad MB3614/LM324 at 7K on the CPU board


Problem: Missing sprites. All motion sprites were missing.

Solution: Bad LS08 at 8L on the video board.

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