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Donkey Kong - garbage on screen



Game - Donkey Kong

Symptoms - Garbage on screen. It boots to the highscore table, but full of junk. From there it moves to the attract mode but mario falls below where he's supposed to be, game resets, and repeats this process. (Ignore the inverted color in the first picture, I didn't have an inverter board on hand).


Solution - The board was originally missing stuff and had previous work (it was an 'untested' special on ebay). The previous work looked fine so I could start. I figured the problem to be a memory issue. I initially started on the CPU board, I figured since the game was resetting it was a CPU board. After probing around I I didn't find anything immediate so I moved to the video board. I started by piggybacking known good RAM chips on the board and saw improvement. It turns out that 2114 RAM had gone bad at location 2P. Socketed and replaced, game is now working great.

Fixed broken images

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How do you piggyback chips? Is it literally sitting one on top of the other so the legs touch?

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10 minutes ago, Lincoln said:

How do you piggyback chips? Is it literally sitting one on top of the other so the legs touch?

Yep. Sometimes it helps, sometimes it doesn't. It is particularly useful with RAM chips if the chip is just corrupting the data, as it can help stitch it together. But if the outputs are stuck low for example, it might not work. It is very important that the chip's pins are tight, otherwise it might not make a good connection.20200630_210831.thumb.jpg.8aa8d94dc188c917d343eb17dd352dcd.jpg

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