Donkey Kong Jr display is wavy, sync problem?

john2654

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Bought a complete "WORKING" 2 board Donkey Kong Jr. set from a KLOV user. Took 3 weeks to receive, but finally got them today. Popped them in and all i get is a scrambled screen as pictured. My previous set worked perfect with the monitor so it isn't that. The only pot that seems to do anything is VR2 which is on the video board. Is the pot bad?
 

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Try adjusting your horizontal hold. It's in the middle of the chassis:

SanyoBoardControls.jpg
 
BTW - the VR2 you are talking about is on the DKjr boards, right? I know those two there can cause this problem if either gets broken....
 
H Hold on the monitor chassis did not do anything. When I received the boards, they were not packaged the best. So a broken VR2 pot (located on DK video board) could cause this? Since VR1 and VR2 are the same value (50K ohms 1/3W), should I try replacing with VR1 pot from old board set?
 
Sure. I have a DKjr board that has a broken pot and won't sync. We swapped in one from a working boardset for testing purposes and it synced just fine. Took it back off to go back to the working boardset, and eventually I'll put a new one on.

You can use a meter to check to see if it measure 50k, and changes smnoothly as you turn it.

I'm assuming you are using a standard Nintendo video cable, and not something homemade? If homemade, then I assume you realize that Nintendo monitors have a different video pinout than normal monitors?
 
Yeah everything is original. Just removed original board set and put in the new set. Old set worked fine except it would reset whenever it would start the game screen. I'll try swapping around pots and measure them. Thanks!
 
Ok, I measured them and they are reading low ohms at first then a slight turn of the knob and the meter spikes all the way up. Is a 50K 0.3 Watt pot ok? Or where can I get replacements and what is the part number? Bob Roberts doesn't state watts, does that matter? Thanks!
 
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Tried swapping pot from old board. It worked perfect until I tried moving knob. The screen was off center. Now I am back to the same wavy picture. Can you give me the Bob Roberts page with the 50K pot and the exact name/part # ? Can't seem to find it. Oh, and does watts matter? I know the original is a 50K ohms, 1/3 Watt pot (.333333). Last time I looked at the pot page he didn't list watts. Thanks!
 
Parts page, about 1/3rd of the way down

Nintendo DK Replacement Pot 30K Ohm $1.00
Nintendo DK Replacement Pot 50K Ohm $1.00
Nintendo DK Replacement Pot Pair 30K Ohm (2) $2.00
Nintendo DK Replacement Pot Pair 50K Ohm (2) $2.00
 
It is usually futile to use pots off of old Nintendo boards, whether it is game boards or monitor boards, as the pots are prone to going bad soon if not already bad. I guess form age. I always replace them all once I start having trouble with one.
 
Found it thanks. So do I need the 50K ohms or 30K ohms pot? It is a 2 set board. Manual states on page 6 that it is a 50K ohm pot, go with that?
 
Replacing the pots fixed my sync problem. One video board works fine, the other will loose sync and mess up if the pot dial is moved - very touchy. I'd call it successful though. Thanks!
 
im having the same problem with my dk not syncing. i just replaced both pots with new ones and it did nothing.

i read this on mikesarcade. does this sound like the next step i should take or am i missing something else? the only thing i see wrong is that the 74ls02 is in location d1 not c1 on my board.


Problem: TKG3 board set - Board will not sync

I replaced the pots and no change. All the LS161/163s were pulsing. Looking at the schematics, there is a 74LS02 connected to the VBLK/CMPBLK outputs. I noticed that if I shorted pins 2 and 3 on the LS02, the picture would semi-straighten up. Replacing the chip fixed the board.

Solution: 74LS02 at 1C on the CLK board at 1C
 
Even installing the new pots you have to be extremely careful. One out of two sets I repaired worked for me. I replaced the pots again and it then worked. Might be something else for you though??
 
i actually got lucky. i adjusted the h-hold (vr451) on the chassis again(first time after the pot change) and she works like a charm. also tested some of my bootleg boards. all three i tested worked although they do come up upside down on the screen. i need to find my falcon to jamma adapter to test the other 2 bootleg boards.

i did test my dk3 and it works great but my dkjr is messed up im going to have to spend a little time with it.
 
I know this is old, but I wanted to post a fix i found that the OP was having with his original board set resetting at the game screen.

I had a board with garbage on the screen. I swapped a known good working 5B EPROM on the board and the game started, but would reset as soon as the game screen appeared. So I swapped in a good working 5C EPROM and the game plays without issue now. I erased and reburned the EPROMs and now I have a working board set.

If you still have this set, hopefully it fixes it, or maybe you sold it, and then I bought it from someone else and solved the issue ;)
 
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