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Donkey Kong TKG-4 Sprites not displaying consistently, flickering


dedmunds

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Hello all

 

I have been finishing a DK build and am getting to a few final little issues.

My main problem left is that the sprites for the game don't display consistently. They tend to 'flicker' on, stay for a moment then disappear, so on.

 

After the cabinet has been powered on between 5-15 minutes, sometimes the display of sprites comes good, and i can play no problem.

 

Who has experience with this kind of issue or possibly a link to any similar cases that i could check?

I have had a browse but i haven't come across anything for this unless I have missed something.

 

I'm pretty keen to understand what any potential causes may be or if anybody's got any suggestions.

 

So far have:

- Noted self-test from High Score board finds no Video RAM or CPU RAM faulty (all ok)

- Confirmed that all text reads perfectly on screen, only issue seems to be with game sprites

- Cleaned board connections for EPROM's

- Removed, cleaned pins and reseated all ROMs (some were horrible), I noted processor chips had very blackened pins, so they been getting hot...

- Confirmed +5, -5, +12 VDC, +12 is reading high but +5 is right on, I believe 5.09VDC at edge connector at last check

 

NOTE: When fiddling with V-Hold and H-Hold i feel this made some difference, but honestly I have messed with it that much I suspect this could have nothing to do with it.

I may be going nuts but i sure am learning a lot!

 

Thanks everyone,

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Hi everyone, quick update.

 

Eventually, the above kinda resolved itself. The board played great for a few weeks. Thought i was in the clear!!

I didn't want to stuff with it, and all seemed to be ok, so i just left it go. I only had the cabinet on while playing, else i just left the cab off.

 

So, NEXT CHAPTER!! But now it is oh so much worse.

Well... Looks worse. Maybe it's simple. Not sure.

 

So, this all came about from last weekend. I powered the cab up and the board was on for maybe... 6 hours or so.

Finally I went to play in the late afternoon and saw this:

bootup1.PNG.57ce42140ab4be80a5d3d71fd00f2297.PNG

 

Left it powered off overnight in case i overdid it and some part had overheated etc...

Anyway, I checked it the next day, no good - still issues.

 

When I tested, I could:

  • Still get bootup noise
  • Game would not coin, or start in background (seemed to lockup)
  • If Hi score kit was installed - would get black screen past boot-up screen
  • If no Hi score kit installed - I would get the above
  • only other thing i'd get would be "J" all the way down the screen below the 1UP text

So i decided it was a bit beyond my skill to heal...

Took this to a friend who repairs boards.

 

Thus far:

  • Checked ROMs, replaced 7C which was faulty
  • CPU ROMset was checked (i believe checksum was okay), replaced as fault find measure

As a result the screen boots to garbled text

2079892314_bootstogarbledgraphics.PNG.ff487fbfb74b69f672edc2589ba97325.PNG

 

The game is still not running in the background, still did not coin and did not start.

 

After this, my mate tracked through and found some problems with what seemed to be faulty SRAMS.

These were removed as below

274968501_boardblackenedbehindSRAMS.PNG.2ca725f14968b07590469c608d8cee96.PNG

 

Note the board spots were blackened just like the pins of the CPU that i mentioned initially. Overall not a great find but the board is a year older than i am, so i guess you gotta expect some deterioration here and there.

 

I have been consulting the guide on Braze Technologies as to common board faults, but nothing is stacking up for me!!

https://www.brasington.org/arcade/tech/dk/

 

I am pretty much running out of ideas fast on this.

Help!!😖

 

@Kaizen - Man if you can lend some experience to this one it'd be really great

 

Thanks all - wow, what an adventure so far!

I just wanted to play DK...

bootup1.PNG.8573183cf2d55b432f06a193fbd60d5b.PNG

Edited by dedmunds
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Assuming your voltage are ok, it's likely a contact issue, the ribbon cable and associated connectors are known to cause issues after nearly 40 years. Ideally you'd replace all board interconnect cables and sockets with new ones but its a sod of a job. They can drive you mad with intermittent flakyness that seems to come and go randomly. Single wipe sockets can cause issues too but the ones on DK are usually pretty robust.

 

It could also be a logic fault, have seen both, but I'd start with the ribbon cables, if they aren't an issue today, they will be at some point.

 

Btw - The black pins on the CPU isn't heat related, those pins were silver plated, the black is a reaction to sulphur dioxide in the atmosphere over many years. The dark spots under the RAM chips is heat related, as those RAMs run pretty hot, totally normal.

 

Also - just check your mate didn't burn 2732s to replace 2532s, they aren't pinout compatible, DK can take both but you'd need to modify the PCB links (from memory) to change the type.

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@Womble Thanks so much for your reply... It was a very short step from last Sunday with a fully working TKG-4 board to now where we are working through issues to get everything working again. Just to you're aware also I did confirm with my mate Tim that he also did replace the ribbon cables, which is good because it's one less thing.

 

Will check in RE the 2532s.

 

Thanks again!

 

 

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Cool, I did wonder as the photo you posted showed what looked like newly labelled 2732s which was probably wrong for a DK.

 

In terms of likelihood, an actual bad EPROM at 5A is pretty low down the list, the fault may be located at 5A but I would double check the chip itself physically first (legs bent under rather than correctly sat in the socket) or tarnished legs. Also check it isn't in backwards, if it has been in backwards when the power was applied then the chip is toast.

 

Also, the sockets on these boards only make contact on the outside of each leg, so I'd make sure the outer edges are clean, you can also very slightly bow the legs outwards a bit, so they press harder on the socket contacts. Tread carefully if doing that as it can make it harder to get the chip back into the socket correctly.

 

Beyond that I'd be point a scope, or at minimum a logic probe at the control signals at that chip, /CE, /OE and /WR, as it is more likely that the board has a logic fault that isn't controlling that chip correctly.

 

But it could be a bad EPROM, or be nothing at all to do with 5A.

 

If was a betting man I'd put money on a logic fault.

Edited by Womble
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