OK, I spent a few hours with this board set tonight.
First, I pulled the stack apart to clean and re-seat chips.
When examining chips on the video board, I noticed that the chip in 5F had a leg that was mashed up between the socket and the belly of the chip. With some patience, a needle nosed pliers and creativity, I was able to straighten out the leg, and get the chip socketed again. I booted the board.
A few more sprites had come back, but not much. Bummer.
So, I referenced the chart found on the Brasington site, found here:
http://www.brasington.org/arcade/tech/dk/
Since I had a fully working 2 board set to work with, I figured I'd start playing hopscotch with eproms to see if I could get some where.
Since it appeared that my moving sprites were big blocks of nothingness, I looked on the chart and saw that 'moving objects' were contained in eproms 4M, 4N, 4R, and 4S. I swapped all 4 of them with known working replacements from my 2 board set.
Here's what I got:
Progress! I now had my moving sprites back, fully drawn. But the colors were all off still. And WTF with the blue background??
So, I kept examining the chart. Color maps are contained in 2K and 2J on the CPU board. OK, so let's swap them.
Then I get this:
Hard to see, but my background is now finally black! And characters are correct colors now too.
So, last color reference on the chart is 5F on the video board. I swap it. No go. But then I notice something: the chip that was sitting in 5F was labeled 2J, which belongs on the CPU board, NOT the video board. It seems someone before me must have gotten 2J and 5F mixed up somehow. So, I traded places with them.
Booted the board, and.....
Garbage on the screen, and SMOKE??? WTF??
Shut it off right away. dammit.
Took a closer look at the video board, which is where the smoke was coming from. Saw a cooked label on the chip in 5F, which was inserted in the socket BACKWARDS. Crap crap crap....I need to pay closer attention....
So I turned the chip around and booted the board again. I was greeted with this:
Yay! Fully working!! WOOT!
So I'm left with 4 eprom chips that I 'borrowed' from my working 2 board set: 4M, 4N, 4R and 4S. I tested each one by themselves in my now working board set, and each one brought back different parts of 'blockiness' back to my moving characters. So there's no doubt about it, I certainly have 4 bad eproms that will need to be reprogrammed.
So....in short:
- Busted adjustment pot causing lost sync
- One of the 256x4 proms had a mashed leg, causing missing graphics (ladders, partial words, etc)
- Two of the 256x4 proms were in the wrong place, causing all sorts of color problems.
- 4 of the video eproms had bad code.