Picked up a short while back from @mysticmonk ... (sprite problems reported) ... board set turned up in good shape ....
But does obviously have an issue with the sprites when the game starts, only half a helicopter (below left) and some other tiles missing or flashing up wrong or in the wrong places ..
The above right picture shows the issue when the player dies - sprite tiles repeated nearby ...
This bootleg pcb is a 3 board stack and Sprites are handled by the pcb below ...
I've marked the 2x 2114 Sprite Attribute Ram in blue as this was where I started to look for faults ... Started with the Oscilloscope and scoping the pins of both ram chips there was activity where there should be and no stuck lines, so I looked at the LS245 buffers nearby which receive the data, these also looked ok on the scope. But I've had it before with these ram failing in ways which aren't obvious on the scope. So I sliced both the ram chips with the following results ...
Now again, the fail on the right (top one of the 2 chips marked in blue) didn't immediately fill me with suspicion because in my experience quite often a small error (numbers 1-10) slice fail doesn't usually mean the IC has definitely failed. So I was about to move on from the RAM altogether, but before looking elsewhere I thought I'll just quickly piggy back that chip to see if it makes any difference .... and it didn't bring back any more of the helicopter at all, or improve the flashing tiles in and around it, but it did make a difference to the player sprite ... some of the extra tiles that were appearing were now not, see pics below (before in small blue boxes)
Sprites weren't showing better ALL the time, but enough to see the piggy back was giving some improvement here and there ... and that was enough to warrant replacing that ram chip ...
Which did the job and fixed the sprites ... now working 100%
So a quick and straight forward one but a reminder not to rely too heavily on one test method, but to use all the tools and methods at your disposal, as one might help highlight an issue that others don't. In this case probably the 2114 Ram had weak output drivers leading to intermittent incorrect reads. Good 'ol piggy back confirmed it failing !
But does obviously have an issue with the sprites when the game starts, only half a helicopter (below left) and some other tiles missing or flashing up wrong or in the wrong places ..
The above right picture shows the issue when the player dies - sprite tiles repeated nearby ...
This bootleg pcb is a 3 board stack and Sprites are handled by the pcb below ...
I've marked the 2x 2114 Sprite Attribute Ram in blue as this was where I started to look for faults ... Started with the Oscilloscope and scoping the pins of both ram chips there was activity where there should be and no stuck lines, so I looked at the LS245 buffers nearby which receive the data, these also looked ok on the scope. But I've had it before with these ram failing in ways which aren't obvious on the scope. So I sliced both the ram chips with the following results ...
Now again, the fail on the right (top one of the 2 chips marked in blue) didn't immediately fill me with suspicion because in my experience quite often a small error (numbers 1-10) slice fail doesn't usually mean the IC has definitely failed. So I was about to move on from the RAM altogether, but before looking elsewhere I thought I'll just quickly piggy back that chip to see if it makes any difference .... and it didn't bring back any more of the helicopter at all, or improve the flashing tiles in and around it, but it did make a difference to the player sprite ... some of the extra tiles that were appearing were now not, see pics below (before in small blue boxes)
Sprites weren't showing better ALL the time, but enough to see the piggy back was giving some improvement here and there ... and that was enough to warrant replacing that ram chip ...
Which did the job and fixed the sprites ... now working 100%
So a quick and straight forward one but a reminder not to rely too heavily on one test method, but to use all the tools and methods at your disposal, as one might help highlight an issue that others don't. In this case probably the 2114 Ram had weak output drivers leading to intermittent incorrect reads. Good 'ol piggy back confirmed it failing !