TL;DR - missing cars and signs sprites caused by bad 74LS298 @ 9D on the video PCB.
After getting past the booting issues, passing all self test etc my PCB booted into the game and appeared to be running the game code fine. Just one small issue, there are no cars, signs or the start/finish gantry! Obviously a racing game without cars isn't much fun so had to fix this one.
To fix this one I was able to use the excellent SLICE tool by GadgetFreak, cross checking with an ABI BM 4000. I can safely say the SLICE was a much easier and quicker tool to use for this!
So the cars, signs, etc are called 'motion objects' in Atari language (Sprites to the rest of us).
Starting at sheet 14b of the schematics I traced where the signals for the sprites are generated and followed them through the circuit (no pun intended).
After checking all the ROMs were getting selected and probing MP1-4 which is the outputs from this part of the circuit - they all seemed to be fine and chirping away as they should.
Moving on to sheet 15a, I found them again present and correct on the 74LS174 @ 11F.
All the inputs and outputs for the 174, 20 and 257s seemed fine. Looking at the other side of the circuit I found a 74LS298 which outputs signals MO1-4. These signals are then combined with other outputs into the final signal sent to the RGB signals to the monitor (on page 15b of the scheme).
I ran the SLICE on the 74LS298 and it showed the output pins MO1-4 were all stuck high.
I retested using the BM4K in circuit test, it also showed it as bad. I removed the IC and plopped a socket it. The old 298 also fails the out of circuit test on the BM4K. Put a new 298 in and booted, we now have cars!
As a final comparison, here is a pic of the SLICE test of the new 298;
After getting past the booting issues, passing all self test etc my PCB booted into the game and appeared to be running the game code fine. Just one small issue, there are no cars, signs or the start/finish gantry! Obviously a racing game without cars isn't much fun so had to fix this one.
To fix this one I was able to use the excellent SLICE tool by GadgetFreak, cross checking with an ABI BM 4000. I can safely say the SLICE was a much easier and quicker tool to use for this!
So the cars, signs, etc are called 'motion objects' in Atari language (Sprites to the rest of us).
Starting at sheet 14b of the schematics I traced where the signals for the sprites are generated and followed them through the circuit (no pun intended).
After checking all the ROMs were getting selected and probing MP1-4 which is the outputs from this part of the circuit - they all seemed to be fine and chirping away as they should.
Moving on to sheet 15a, I found them again present and correct on the 74LS174 @ 11F.
All the inputs and outputs for the 174, 20 and 257s seemed fine. Looking at the other side of the circuit I found a 74LS298 which outputs signals MO1-4. These signals are then combined with other outputs into the final signal sent to the RGB signals to the monitor (on page 15b of the scheme).
I ran the SLICE on the 74LS298 and it showed the output pins MO1-4 were all stuck high.
I retested using the BM4K in circuit test, it also showed it as bad. I removed the IC and plopped a socket it. The old 298 also fails the out of circuit test on the BM4K. Put a new 298 in and booted, we now have cars!
As a final comparison, here is a pic of the SLICE test of the new 298;
