21 Jun 2017

Black Dragon - Capcom 1987 (repair log)

Great story about this game. I got it in a local auction for $1 (the minimum bid) thanks to my friend Kelvin who sent me the link.

I placed only one bid and then forgot about the auction. I had set a reminder in my phone but mistankenly entered the wrong time. So I got the reminder 40 minutes after the end of the auction. When I switched off the alarm I saw I had an email on my phone. It was the auction site confirming I won the auction! Nobody else bidded. Probably cause the board was advertised as faulty and there are very few arcade repairers over there in New-Zealand.

When I received the board I promptly noticed the game has been repaired before as the work RAM had been put on a socket. For once it was a clean job so this didn't bugger me. Otherwise it was in very good nick.
I powered it and was really surprised to see the game was almost 100% perfectly running (and discovered it was the Japanese version of the game "Black Dragon" despite the seller advertising it as "Black Tiger"). Only fault I could find was when the sprites were close to either the left or the right border they were repeated on the other side with jailbars on them.

 
As always I identified the function of each RAM, piggybacked them and probed few IC with no clear culprit. To me it was a counter issue (I found a LS163 next to the sprites RAMs) but before spending more time on the board I contacted Caius from JAMMARCADE who confirmed what I thought: probable counter issue.

I went back to the repair and probed all the LS163 of the video board. One of them had pin 10 not connected to anything. This surely wasn't normal as it's the CET input. I couldn't figure out where it should be connected. So I pulled the chip to see the traces underneath. After doing so I was left with only one possibility: trace going to pin 7 was the only possible trace that could be connected to pin 10. I compared with others LS163 on the board and surely pins 7 and 10 were bridged. I installed a socket, put back the chip in it and ran a wire between pins 7 and 10. Problem vanished.


I then spent the rest of my afternoon playing the game as it's one of my favorites.

Game fixed.

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