Got hold of another bombjack bootleg pcb with jamma harness from a member, he stated it worked ok apart from corrupted graphics. Here's it on my work bench.
Nice condition and no missing parts,powered on and the game booted and appeared to be working with audio but I noticed the picture on my tv was very dark ?
I suspected something regarding low volts,as I increased the +5v the picture became a little more brighter but leaving it at 5.8 volt is not a good idea.using my multimeter I checked the +5v at the games edge connector and I got this.
That's way to low,at the jamma card I got 5.25 which is ok,looking close at the jamma card there should be ground wires at pad 27/28 (circled in green) and bottom pads which should go to the edge connector.This explains the low volts as there is no proper gnd path return for the high current. Also noticed the player 2 controls are not wired(circled in red)
I wired this jamma harness correctly and powered on,right that's better and the volts at the edge connector is exactly at +5 volts
.
Right now we have a proper Image on the screen and I can clearly see that the background tile graphics are corrupted in certain areas such as the sphinx head and pyramid also other levels backgrounds are a mess,all sprites foreground, text are fine. Worked out the graphics roms are on the top pcb.
By shorting out some address pins on one of the bgtiles roms I saw a change in graphics on the background. Decided to pull all roms and did a romident and they checked out ok so we can rule out the roms for data corruption. This fault is more likely going to be a addressing issue so I scoped all the data and address pins on eprom 8L and they were all active at ttl.looked at the schematics and these addressing signals come from a 74ls273 at location 6s.
I did a piggy back on this ls273 but the result was no change, I spent another hour looking at the tiles generation circuit but couldn't find any signs of fault 😩. Went back to this LS273 and made a closer look at the outputs and did noticed 2 of the outputs looking flaky,decided to remove this for a new one and.......
🤪 At last it worked,played it for an hour and worked flawlessly. Added a heatsink on the amp and fitted to leds just as it was on the original pcb.
Another one saved.
Nice condition and no missing parts,powered on and the game booted and appeared to be working with audio but I noticed the picture on my tv was very dark ?
I suspected something regarding low volts,as I increased the +5v the picture became a little more brighter but leaving it at 5.8 volt is not a good idea.using my multimeter I checked the +5v at the games edge connector and I got this.
That's way to low,at the jamma card I got 5.25 which is ok,looking close at the jamma card there should be ground wires at pad 27/28 (circled in green) and bottom pads which should go to the edge connector.This explains the low volts as there is no proper gnd path return for the high current. Also noticed the player 2 controls are not wired(circled in red)
I wired this jamma harness correctly and powered on,right that's better and the volts at the edge connector is exactly at +5 volts
.Right now we have a proper Image on the screen and I can clearly see that the background tile graphics are corrupted in certain areas such as the sphinx head and pyramid also other levels backgrounds are a mess,all sprites foreground, text are fine. Worked out the graphics roms are on the top pcb.
By shorting out some address pins on one of the bgtiles roms I saw a change in graphics on the background. Decided to pull all roms and did a romident and they checked out ok so we can rule out the roms for data corruption. This fault is more likely going to be a addressing issue so I scoped all the data and address pins on eprom 8L and they were all active at ttl.looked at the schematics and these addressing signals come from a 74ls273 at location 6s.
I did a piggy back on this ls273 but the result was no change, I spent another hour looking at the tiles generation circuit but couldn't find any signs of fault 😩. Went back to this LS273 and made a closer look at the outputs and did noticed 2 of the outputs looking flaky,decided to remove this for a new one and.......
🤪 At last it worked,played it for an hour and worked flawlessly. Added a heatsink on the amp and fitted to leds just as it was on the original pcb.
Another one saved.
