Monstermug
Active member
Got a Alcon on my bench today. I had previously worked on this board to revive it from the dead but it had a very slight graphics glitch and I had stored it away for a few years hoping that the fault would miraculously go away.
Dug the board out today and the fault was still there obviously.
Fault was that everything looked fine except that during gameplay and attaract sequence, when the player ship was directly in front of any sprite objects, the object would fade away, with some disappearing altogether. When the ship moved away from underneath it, the sprite would return back to normal.
That object looks faded away when ship directly underneath it.
When ship is on the side of it the object comes back.
First thing to do was to verify roms against mame romset. What I found weird was that when I verified ROM A77 07 and A77 08 at locations M6 and K6 respectively they failed. When burnt roms from Mame romset for Alcon, I got dodgy background colours. (all the other roms were for Slapfight). In the end I had to reburn what was originally on there back onto the ROM and deemed it okay as it wasn't a sprite rom anyway and the colors were originally fine.
Found that the sprites roms were on the TOP layer board and all the associated circuitary that controls the sprites. I believe that A77 09 - 12 were ROMs in charge of Sprites. They verified fine. I didn't expect them to verify wrong anyway but it's always good to make sure since it doesn't take any effort to do so. The reason I didn't expect them to be bad was because the actual sprites image were present just something in the address circuitry causing sprites to get not drawn properly when needed.
Now I decided to check the sprite rams to see if address lines were okay. Found a bank of rams next to the sprite roms.
These are D4364C. Probing the address lines with the logic probe revealed that address line A8 on pins 25 on each of the Rams were stuck high when they should be pulsing.
The next half hour was spent drawing out the a basic schematic as just trying to trace the signal down the lines was hard to remember and seeing what I could learn.
Very crude schematics which was drawn out on the fly.
Basically everything seemed to point to a bad 74LS283 at locations F4. Outputs were tied high and inputs tied low when they should have been pulsing.
As it was a Fujitsu chip I didn't have any second thoughts of pulling it out.
Chip tester says it's bad but there's only one for sure way to really find out! And that's to put a new one in!
No more fading away
Even when ship directly underneath it!
Another game 100% fixed.
Dug the board out today and the fault was still there obviously.
Fault was that everything looked fine except that during gameplay and attaract sequence, when the player ship was directly in front of any sprite objects, the object would fade away, with some disappearing altogether. When the ship moved away from underneath it, the sprite would return back to normal.
That object looks faded away when ship directly underneath it.
When ship is on the side of it the object comes back.
First thing to do was to verify roms against mame romset. What I found weird was that when I verified ROM A77 07 and A77 08 at locations M6 and K6 respectively they failed. When burnt roms from Mame romset for Alcon, I got dodgy background colours. (all the other roms were for Slapfight). In the end I had to reburn what was originally on there back onto the ROM and deemed it okay as it wasn't a sprite rom anyway and the colors were originally fine.
Found that the sprites roms were on the TOP layer board and all the associated circuitary that controls the sprites. I believe that A77 09 - 12 were ROMs in charge of Sprites. They verified fine. I didn't expect them to verify wrong anyway but it's always good to make sure since it doesn't take any effort to do so. The reason I didn't expect them to be bad was because the actual sprites image were present just something in the address circuitry causing sprites to get not drawn properly when needed.
Now I decided to check the sprite rams to see if address lines were okay. Found a bank of rams next to the sprite roms.
These are D4364C. Probing the address lines with the logic probe revealed that address line A8 on pins 25 on each of the Rams were stuck high when they should be pulsing.
The next half hour was spent drawing out the a basic schematic as just trying to trace the signal down the lines was hard to remember and seeing what I could learn.
Very crude schematics which was drawn out on the fly.
Basically everything seemed to point to a bad 74LS283 at locations F4. Outputs were tied high and inputs tied low when they should have been pulsing.
As it was a Fujitsu chip I didn't have any second thoughts of pulling it out.
Chip tester says it's bad but there's only one for sure way to really find out! And that's to put a new one in!
No more fading away
Even when ship directly underneath it!
Another game 100% fixed.
