Hiya
I recently bought a non working capcom 1943 off a member on here, so here is what happened, the sprites and the background had faults.
I first looked at the background troubles, then the clouds dropped down the screen there was red chunks coming down with the clouds! you can see it in the pic, on the left and near the top of the screen. Also the ship had a extra red and blue 'blob' on one side of its hull!
bit of prodding and poking and found ROM 10F was dud! a couple of the pins were bad so it was trying to work!
next I noticed when the plane animates on the hi score screen a couple of the pictures was bad but it ended up with the last pic it produces being fine!
so a bit more poking and prodding and this time found ROM's 11J and 12J again with internally non connected pins! so background graphics now ok!! time to look at the sprites!
Went straight for the memory for that!nope they was innocent! memory tested fine and there outputs was good!
A study of the sprites in freeze mode revealed the sprites were actually there, just one was misplaced with respect to the other
Look carefully and you can see the other half of the planes above!
so there misplaced vertically to each other!
When poking around again with the oscilloscope I found the side that was at fault was the line buffer 2 circuit and the RAM 12D was not having A8 change half as much as its counterpart 7D
This A8 comes from 12E which of course was fine and innocent! next in line working back was 10E pin 15 was wrong, only a few pulses from this when there should have been lots! again the 74LS163 was innocent!! so that means its inputs must be at fault, this was hard to understand as both this and the other ram had the same signals being fed to them and the other RAM line was fine!
VERY VERY careful inspection (and then comparison with a bootleg board) found that signal DF5 being fed to pin 4 of the 74LS163 at 10E Was indeed very slightly sitting on the ground line compared to the other lines DF4, 6 and 7!
this is a good pin DF4
Between the bright bits is the data! difficult to see and take a pic off but it is there! on the faulty pin it was like this...
OK it looks more different in the picture than it did in real life!!
tracing it back and ...... it comes out of that big custom chip!!! looking at all its inputs.... fine nothing wrong!!
I can only assume the data on the DF5 line is present and correct for the RAM at 7D but not for the RAM at 12D!
very odd!!!! has anyone else come across this type of fault??
That took about a day and a half going round in circles! so you win some and you loose some, this one I lost out on a lot! just my luck!!
Andrew
I recently bought a non working capcom 1943 off a member on here, so here is what happened, the sprites and the background had faults.
I first looked at the background troubles, then the clouds dropped down the screen there was red chunks coming down with the clouds! you can see it in the pic, on the left and near the top of the screen. Also the ship had a extra red and blue 'blob' on one side of its hull!
bit of prodding and poking and found ROM 10F was dud! a couple of the pins were bad so it was trying to work!
next I noticed when the plane animates on the hi score screen a couple of the pictures was bad but it ended up with the last pic it produces being fine!
so a bit more poking and prodding and this time found ROM's 11J and 12J again with internally non connected pins! so background graphics now ok!! time to look at the sprites!
Went straight for the memory for that!nope they was innocent! memory tested fine and there outputs was good!
A study of the sprites in freeze mode revealed the sprites were actually there, just one was misplaced with respect to the other
Look carefully and you can see the other half of the planes above!
so there misplaced vertically to each other!
When poking around again with the oscilloscope I found the side that was at fault was the line buffer 2 circuit and the RAM 12D was not having A8 change half as much as its counterpart 7D
This A8 comes from 12E which of course was fine and innocent! next in line working back was 10E pin 15 was wrong, only a few pulses from this when there should have been lots! again the 74LS163 was innocent!! so that means its inputs must be at fault, this was hard to understand as both this and the other ram had the same signals being fed to them and the other RAM line was fine!
VERY VERY careful inspection (and then comparison with a bootleg board) found that signal DF5 being fed to pin 4 of the 74LS163 at 10E Was indeed very slightly sitting on the ground line compared to the other lines DF4, 6 and 7!
this is a good pin DF4
Between the bright bits is the data! difficult to see and take a pic off but it is there! on the faulty pin it was like this...
OK it looks more different in the picture than it did in real life!!
tracing it back and ...... it comes out of that big custom chip!!! looking at all its inputs.... fine nothing wrong!!
I can only assume the data on the DF5 line is present and correct for the RAM at 7D but not for the RAM at 12D!
very odd!!!! has anyone else come across this type of fault??
That took about a day and a half going round in circles! so you win some and you loose some, this one I lost out on a lot! just my luck!!
Andrew
