Recently won this awesome horizontal shooter on ebay, seller stated it worked but there was a sound issue. Could this be a easy fix 
🤞,from experience sound faults can be quite difficult to fix.So here it is on my bench, quick visual inspection of the pcb was that it was in good condition and no broken components. 
Ok let's fire it up, cool the game booted and rom and ram check was good 👍,and yes there was no sound but some random chirping only.just to confirm the amp was OK I touched pin 1 of the amp and a hiss was heard so that confirmed the amp was good. There is no schematics for this game so I went straight to the sound Z80cpu with my scope so we have a nice clock signal, NMI high (good),INT fluctuating (not good),RD signal (present),WR signal (present),RESET toggling (not good).when there's a toggling reset pin on the z80 this indicates the watchdog is barking so more likely there's a problem on either the databus or address bus,started to check all the data pins on the z80 which were active until I looked closely at data D0 at pin 14 and the signal should be close to TTL but it was 2.8v,so this must be the issue where the z80 is not running. Close to the z80 we have the 6264 audio sram,oki 6295 speech chip,2x ym2203 music chips.All these components share the databus so any of these can stop the Z80cpu from running,I removed the 6264 and placed in a new one but issue was same,isolated pin 37 of the oki 6295 but no go.
Pin 40 of both ym2203 is also data bit D0 so I snipped them to isolate.
And this time we had a TTL D0 signal, so lets find the smoking gun.The culprit was the ym2203 at location 5C so it was removed.
New socket installed and popped in a new ym2203, fired it up and ohhhhh yes we have sound and samples back.played it for an hour and worked flawlessly, what a great shooter it's similar to r-type style of game.
If anyone is interested in buying this please get in touch.
🤞,from experience sound faults can be quite difficult to fix.So here it is on my bench, quick visual inspection of the pcb was that it was in good condition and no broken components. Ok let's fire it up, cool the game booted and rom and ram check was good 👍,and yes there was no sound but some random chirping only.just to confirm the amp was OK I touched pin 1 of the amp and a hiss was heard so that confirmed the amp was good. There is no schematics for this game so I went straight to the sound Z80cpu with my scope so we have a nice clock signal, NMI high (good),INT fluctuating (not good),RD signal (present),WR signal (present),RESET toggling (not good).when there's a toggling reset pin on the z80 this indicates the watchdog is barking so more likely there's a problem on either the databus or address bus,started to check all the data pins on the z80 which were active until I looked closely at data D0 at pin 14 and the signal should be close to TTL but it was 2.8v,so this must be the issue where the z80 is not running. Close to the z80 we have the 6264 audio sram,oki 6295 speech chip,2x ym2203 music chips.All these components share the databus so any of these can stop the Z80cpu from running,I removed the 6264 and placed in a new one but issue was same,isolated pin 37 of the oki 6295 but no go.
Pin 40 of both ym2203 is also data bit D0 so I snipped them to isolate.
And this time we had a TTL D0 signal
, so lets find the smoking gun.The culprit was the ym2203 at location 5C so it was removed.New socket installed and popped in a new ym2203, fired it up and ohhhhh yes we have sound and samples back.played it for an hour and worked flawlessly, what a great shooter it's similar to r-type style of game.
If anyone is interested in buying this please get in touch.
