darthsylly
User
It's my first PCB repair so I went in at the deep end with a SegaSonic The Hedgehog PCB I've had for a couple of years.
The symptoms were no sound and although the game logic was playing, some sprites were up-side down (while the backgrounds were correct) and others were a little mixed up...
I have a second PCB and was able to swap the ROM boards around to confirm that it was definitely a System 32 motherboard fault.
After examining the underside of the board I spotted some damage to 4 traces which someone had previously repaired:
It looked like the fourth trace from the left wasn't properly connected so I traced it back to a 74244 and put in a jumper wire:
Which led to:
Much better. All sprites and orientation restored. That trace led to one of the Sega customs that handles sprites.
I tinned the trace and took a strand of stranded wire to make the repair more permanent:
The visuals were restored but when you started the game none of the events would occur. At the start, Sonic is normally pushed down the slope by falling lava but here I was able to stand still until the game timed-out and no lava came:
This is a symptom of suicide. My other board has desuicided ROMs so I read those and burnt them onto this ROM board. These are the ROMs that handle the program data:
A quick erase with my cheap UV eraser and they were blasted fresh:
FYI the ROMs are 27c210As and I just used a MiniPro to read and write them, no problem. The MiniPro's preset for this ROM writes at 13V but needs to be put down to 12.5V to work.
With the desuicided ROMs in place the game played properly, here's the lava coming to get Sonic:
The last problem was the audio. Turning the volume pot gave a lot of crackle which suggested something was coming through and the circuits weren't completely dead.
A RAM test showed IC16 was faulty:
Which is this one on the board:
The dreaded 'F'!
Looking at the System 32 specs, the audio is run from a Z80. Since this RAM is right next to it, it seemed fair to think that this was the culprit.
Even with a nice Hakko gun the chip did not want to come off and I ended up snipping the legs. One socket and a known good chip later the board looked like this:
And audio was back
Board repaired!
Naughty pile? Just one bad Fujitsu RAM.
Both my SegaSonic boards are covered in these Fuji chips so I expect plenty more failures over time.
darthsylly2016-03-27 20:57:03
The symptoms were no sound and although the game logic was playing, some sprites were up-side down (while the backgrounds were correct) and others were a little mixed up...
I have a second PCB and was able to swap the ROM boards around to confirm that it was definitely a System 32 motherboard fault.
After examining the underside of the board I spotted some damage to 4 traces which someone had previously repaired:
It looked like the fourth trace from the left wasn't properly connected so I traced it back to a 74244 and put in a jumper wire:
Which led to:
Much better. All sprites and orientation restored. That trace led to one of the Sega customs that handles sprites.
I tinned the trace and took a strand of stranded wire to make the repair more permanent:
The visuals were restored but when you started the game none of the events would occur. At the start, Sonic is normally pushed down the slope by falling lava but here I was able to stand still until the game timed-out and no lava came:
This is a symptom of suicide. My other board has desuicided ROMs so I read those and burnt them onto this ROM board. These are the ROMs that handle the program data:
A quick erase with my cheap UV eraser and they were blasted fresh:
FYI the ROMs are 27c210As and I just used a MiniPro to read and write them, no problem. The MiniPro's preset for this ROM writes at 13V but needs to be put down to 12.5V to work.
With the desuicided ROMs in place the game played properly, here's the lava coming to get Sonic:
The last problem was the audio. Turning the volume pot gave a lot of crackle which suggested something was coming through and the circuits weren't completely dead.
A RAM test showed IC16 was faulty:
Which is this one on the board:
The dreaded 'F'!
Looking at the System 32 specs, the audio is run from a Z80. Since this RAM is right next to it, it seemed fair to think that this was the culprit.
Even with a nice Hakko gun the chip did not want to come off and I ended up snipping the legs. One socket and a known good chip later the board looked like this:
And audio was back
Board repaired!
Naughty pile? Just one bad Fujitsu RAM.
Both my SegaSonic boards are covered in these Fuji chips so I expect plenty more failures over time.
darthsylly2016-03-27 20:57:03
