So I've had this boot XX Mission PCB for a while and while the sprites and text were OK it had no scrolling background.
There's very little info about this boardset and no schematics.
I figured a missing background should be fairly easy to fix but this one had me stumped for ages.
I had put it to one side for quite a while but I revisited it determined to sort it out.
Que long sessions of slicing most of the chips (this is a double layer PCB) and finding nothing.
I had determined where the scrolling was handled. It's a bunch of LS151 and LS164 chips:
I found one bad LS151 but changing that made no difference.
Checking the chips again last night to get some clue as to why the backgrounds weren't working I noticed the select pins of the 151s weren't active-they were all low. I hadn't noticed this before since when I use the slice I'm looking for errors and I was unfamiliar with LS151 chips so wasn't looking for anything like that.
Anyway I found that for all four of the LS151s the select pins (pin 9,10 and 11) were connected across all the chips. These were connected to the LS86 you can see on the far left of the second to the bottom row.
This chip was working fine but without activity so following the inputs to that lead to the other PCB and to my surprise they went to the yamaha 2203 sound chips. WTF????
I had been ignoring those as I wanted to get the rest of the boardset working before I looked at the sound. I dug out a couple of spare 2203 chips anyway and with the known working chips in I got my backgrounds.
No wonder it took a while-I never would have guessed the sound chips are part of background generation.
There's very little info about this boardset and no schematics.
I figured a missing background should be fairly easy to fix but this one had me stumped for ages.
I had put it to one side for quite a while but I revisited it determined to sort it out.
Que long sessions of slicing most of the chips (this is a double layer PCB) and finding nothing.
I had determined where the scrolling was handled. It's a bunch of LS151 and LS164 chips:
I found one bad LS151 but changing that made no difference.
Checking the chips again last night to get some clue as to why the backgrounds weren't working I noticed the select pins of the 151s weren't active-they were all low. I hadn't noticed this before since when I use the slice I'm looking for errors and I was unfamiliar with LS151 chips so wasn't looking for anything like that.
Anyway I found that for all four of the LS151s the select pins (pin 9,10 and 11) were connected across all the chips. These were connected to the LS86 you can see on the far left of the second to the bottom row.
This chip was working fine but without activity so following the inputs to that lead to the other PCB and to my surprise they went to the yamaha 2203 sound chips. WTF????
I had been ignoring those as I wanted to get the rest of the boardset working before I looked at the sound. I dug out a couple of spare 2203 chips anyway and with the known working chips in I got my backgrounds.
No wonder it took a while-I never would have guessed the sound chips are part of background generation.
