SNK Prehistoric Isle Arcade PCB Missing Graphics/Lines In Sprites Repair

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    • SNK Prehistoric Isle Arcade PCB Missing Graphics/Lines In Sprites Repair

      Repaired by: lukemorse1
      Symptoms: Missing colors, Missing sprites, Lines in Sprites.

      Long story short, In December 2018, I bought this board (Prehistoric Isle) off of Fleabay claimed to be tested and listed at 100% working. After receiving it in the mail and ready to play it, Upon first start up, the board was obviously 100% messed up.

      As you can see here, this is what I was presented with when I powered up of the game. It basically looked like SNK were trying thermal imaging on this one as part of a special project, but it wasnt.

      Other parts of the game had lines through the graphics like these here I started to look over the board and found several dead insects, rust, and corrosion as well as many eaten traces on the board. Normally I dont mind picking up broken boards to mess around with but this was a game that I really wanted and since it was listed in 100% working order, that is what I expected, not this.

      I contacted the seller (who was very reasonable to talk with), I explained the situation and how I wasnt too pleased about not getting a working board. He was nice enough and explained that he had tested it and it was working before he put it into storage and he had no idea about the issues with the board. He offered me a partial refund on the board if I wanted to keep it and may know me but.....I decided to take the deal. There were a couple of resistor packs missing from the board as well which I thought might have been the issue and I asked him if he could locate them or find where I could get some. He honestly tried to help out and locate them but he couldnt. Since I had never worked on this particular board before, I didnt know if they were necessary or not.

      Doing some research, testing, trial and error as well as asking around, I found that the resistor array on the top board werent necessary in the missing section and were a common part to "fall off". The downside to finding out this information was that this now meant that the board had much bigger problems than I knew.

      Anyway, I told him that I would try to get it fixed and Ill do what I can to get it going again and that was the end of that.

      Over the course of a couple of weeks I looked over the board finding an overwhelming number of broken/rotten/eaten traces everywhere. It got to a point where finding traces under chips and connectors was just too much work and stressful that It was hard to keep searching this board. I didnt know if I had made the right decision in keeping the board or not by this time . The points I repaired seemed to lead to another and another hidden trace so I put it aside for a few weeks and just worked on it on and off. This "On and Off" lasted over the course of 9 months until I picked it back up again today to try my "luck".

      Here are a few of the traces that you CAN see and then there are half a dozen you CANT see, located under the connector and a few chips. A couple of the worst ones were under CN1 and CN2 but with the corrosion on the pins on the underside it made desoldering a nightmare.……bc9b8bc29d84b9e33bc1751f3On top of this, trying to locate some of these traces was really difficult because some of them werent even obvious. The solder masking on many traces looked ok when in fact they werent ok, and other traces that looked eaten away were actually OK. It was like a hit and miss game with my continuity meter trying to choose which to test. This board being 2 layers didnt help one bit at all either as although the graphics were stored in the bottom half of the board, the connectors and chips on the top half were also eaten away. Arrgh...

      Although it took a long time to work on, I was making progress little by little which is why I stuck with it and didnt decide to get rid of it. As you can see from the pictures below, the graphics, especially the foreground ones and text were coming back once again. This was promising and lead me to continue trying. I managed to get the board running 90% but I hit a wall with it. No matter what I seemed to do, I just couldnt find that final trace (which I thought it was at the time) and this lasted forever.
      I took the board out of my "needing repair" pile of boards last night and thought I would give it another go. (Seriously loving the punishment I think).
      The last step was to find out what where the missing background graphics were and after going over the board over 100 times in a 9 month period, I realized that I had literally ruled out any more broken traces so I was done with those. This meant it must be one of the Roms but which one? I replaced roms GT11 and GT15 as they were too far gone with rust but those changed nothing. My focus then turned to the 2 mask roms PI8914 and PI8916. Not knowing which controlled what, I I had desoldered PI8916 and put in a socket before so it was easy to take out.
      I tested the board without the chip and it was apparent that the foreground graphics were gone for the most part but removing it showed no sign of improvement in graphics anywhere (at this point the foreground was fine, it was the background I needed to work on).

      The second mask rom, PI8914 was removed next. I had also socketed this mask rom before so once again, it was easy to take out. I noticed that after taking it out and powering it up, ALL background graphics disappeared. I could see there were some dead insects under the chip before but traces looked like new. Although I was pretty confident that these were good, I still decided to check them anyway. They all tested fine so my attention went back to the mask rom. I went online and downloaded the mame rom for prehistoric isle and burned the appropriate chip at location B. After replacing it I crossed my fingers, flipped on the power, and..........was pleasantly surprised to see that EVERYTHING was back to normal again. 100%...Finally, like the listing had said lol.
      Letting it run through demo mode as well as trying to get into the game confirmed that all graphic issues had been cleared up.

      This was a long adventure that had finally come to an end and although it took a long time to get it going, I can write it off as another board saved from the grave.
      Below is the Youtube video on this board in a bit more detail for those interested.
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    • xodaraP wrote:

      I hate trace repair when this happens, got a couple in my to do pile I've been working on that are similar to this and like you, I work on them here and there.

      Glad to see there is light at the end of the tunnel!

      Good job!
      For sure. Just trying to work on these voards from time to time but trace repair is a pain lol.
      Glad to have been able ti repair this one and hope you can do the same with yours as well. Thanks a lot