Altered Beast sound issue

mahnomen

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I bought a Altered Beast, that had a dead switching power supply, and monitor chassis. I replace the power supply, dialed in the correct voltages, and replaced the chassis, and can now get the game to fire up and play. However, I cant get any sound.....any ideas where to look, and what to look for?
 
Without being an expert, I can give a pretty probable diagnosis. . .the Suicide Battery. Very common with this board because of the age. Go to sega resurrection.com for more info on the suicide battery and replacement.
 
A dead encrypted Z80 is the most likely cause of missing audio, a few early System 16 games like this title had the encryption on the audio CPU, so when that died the game would still run without any sound. Most System16 games ended up with an encrypted 68000 CPU so when that died the board would do nothing at all.

Basically you need either a

1) working encrypted Z80 AND the original encrupted sound EPROM, the batteries in the encrypted CPUs are now well over 20 years old and are essentially unreplaceable.

or

2) a normal Z80 and a new ROM containing the decrypted sound program code.

Its not uncommon to find people have swapped the Z80 for a standard one but leave the original encrypted ROM still in place, you need both for it to work.

A final possibility is corner damage on the motherboard, the 8 bit data bus for the sound system runs right around the back edge of the board, have seen a few where damage to one of the rear corners has broken a couple of the tracks, this will crash the sound system of the board giving silence usually.
 
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