Tech: Donkey Kong - Can't get screen to lock in on boot up.

barakawins

Well-known member

Donor 2023
Joined
Nov 14, 2004
Messages
2,708
Reaction score
240
Location
Woodcliff Lake, New Jersey
Tech: Donkey Kong - Can't get screen to lock in on boot up.

I have a fully working donkey kong. Rebuilt power supply. Every time I boot up Donkey Kong I get the HZ hold position screen where it scrambles. Turning the game off and then back on, the game comes up and stays on fine. No problems. Adjusting the pots on the pcb doesn't seem to lock the screen on when it boots up either. I put a DK Jr. Board in and it comes up fine. Is there some other adjustment I should be exploring to make the DK board come up without having to shut down and turn back on?

Thanks.
 
Based on the fact that your DK Jr. board works fine, it's probably the hold pots on the DK board going bad. They're notoriously flakey.
 
If you're feeling lucky you could try adjusting the H-Hold that's in the center of the chasis above the flyback (keep in mind that the monitor is vertically mounted so when the H Hold is off the screen will be vertically scrambling/rolling). The only thing about that H-Hold is that pot can be flakey too and hard to dial in. I'd do a lot of fiddling with your PCB pots to make sure they're not the cause before messing with the H-Hold.
 
I have a fully working donkey kong. Rebuilt power supply. Every time I boot up Donkey Kong I get the HZ hold position screen where it scrambles. Turning the game off and then back on, the game comes up and stays on fine. No problems. Adjusting the pots on the pcb doesn't seem to lock the screen on when it boots up either. I put a DK Jr. Board in and it comes up fine. Is there some other adjustment I should be exploring to make the DK board come up without having to shut down and turn back on?

There's 2 pots on one of the PCB's (don't know which one on a 2-board set. It's on the CLK board on the 4-board set. I think it's the ones JamBurglar is talking about). Maybe one of those is bad, or needs tweaked.
 
Pots

Strangely enough.. I already did replace both pots with brand new ones from Bob Roberts and they still don't dial in. I have a funny feeling it's the horizontal pot on the chassis. I'll have to move it a tad just to see if it straightens things out. The DK Jr. Board that I swapped in wouldn't dial in either. Adjusting the pots on the DK Jr board would not bring the screen up. What would happen is that I would adjust the pots on the board to stabilize the warped screen. I would shut down and then turn on. The DK would come up without a problem. But, I couldn't get the picture to come up by just adjusting the pots while looking at the screen. Shutting down and putting back on solved the warped screen image. I think it may be the hz control by the flyback as mentioned. I'll try that this weekend.
 
Strangely enough.. I already did replace both pots with brand new ones from Bob Roberts and they still don't dial in. I have a funny feeling it's the horizontal pot on the chassis. I'll have to move it a tad just to see if it straightens things out. The DK Jr. Board that I swapped in wouldn't dial in either. Adjusting the pots on the DK Jr board would not bring the screen up. What would happen is that I would adjust the pots on the board to stabilize the warped screen. I would shut down and then turn on. The DK would come up without a problem. But, I couldn't get the picture to come up by just adjusting the pots while looking at the screen. Shutting down and putting back on solved the warped screen image. I think it may be the hz control by the flyback as mentioned. I'll try that this weekend.

You need to recap the monitor, this is a common problem when the caps are failing.
 
I have a board on the bench right now with a similar problem. The board plays fine but constantly rolls left to right. VR2 on the pcb does nothing when adjusted. I replaced both pots and tested them to be sure they are working like they should.
This is running on my bench with a lcd screen. I have had several other dk boards running fine on the same rig so I know its the pcb itself. If I find the problem I will post it here.
 
cool

Hopefully you find it. I get the screen rip which is hz sync. I just can't get this thing to lock in. The only way it locks in is if I power down and back on and then the screen comes up fine without any issue. It's gotta be the board I'm thinking.
 
My DK has a similar issue. Monitor is capped, works fine with other boards. With my DK its fine at first, then ill notice a slight shaking left to right, its not terrible, but its not right either. Ive moved the POTS one goes up and down, the other kicks the game out of sync and it wont come back until i power off then back on. I still have not replaced the pot yet, but thought I would share that I am having the same problem. If you figure your issue out, post it, ill do the same if I fix mine.
 
Fixed.
It was a cracked trace under the pot. Explains why the pot was testing good but not responding to adjustment. I realized it when I was measuring voltage at the pot while it was running and the screen locked for a second.
 
Back
Top Bottom