Fixing an original double dragon that has sound problems.
The issue was with the sound samples.
Like when the garage door opens instead of the engine rev there was the sound of the big dude throwing you and a death sound.
Checked the sound roms and they were fine so next checked the addressing of the 27512 roms that handles the samples.
Found the address lines to IC94 (sample rom) came from IC27 (74LS163) and bit 16 going to pin 1 of the rom was changing on the sample being played but not going back after the sample was finished so any subsequent sample was wrong.
Turns out that the 74LS163 at IC27 was a Fujitsu.
Piggybacked a known good chip and the samples were fine.
Replaced IC27 with a socket and fitted a new chip and the samples are fixed.
Now there is also a small graphic glitch on the left of the screen that I think is probably down to another Fujitsu so will try some more piggybacking on the Fujitsus on the graphics board and see if I can find the fault by elimination.
The issue was with the sound samples.
Like when the garage door opens instead of the engine rev there was the sound of the big dude throwing you and a death sound.
Checked the sound roms and they were fine so next checked the addressing of the 27512 roms that handles the samples.
Found the address lines to IC94 (sample rom) came from IC27 (74LS163) and bit 16 going to pin 1 of the rom was changing on the sample being played but not going back after the sample was finished so any subsequent sample was wrong.
Turns out that the 74LS163 at IC27 was a Fujitsu.
Piggybacked a known good chip and the samples were fine.
Replaced IC27 with a socket and fitted a new chip and the samples are fixed.
Now there is also a small graphic glitch on the left of the screen that I think is probably down to another Fujitsu so will try some more piggybacking on the Fujitsus on the graphics board and see if I can find the fault by elimination.