Double Dragon Arcade - No Sound 1987 Arcade Board Repair
Technos Japan Double Dragon(1987)
The board arrived says there is no sound. The board is in a used condition, the top PCB board has significant wrapping. Otherwise there’s no visible damage.
Diagnosis
Tried to boot, played fine with no sound. Turns out -5V is needed for preamps. Supplied with -5V and sound came out but noisy, one of the fighting SFX is missing.
IC97 4558D OpAmp has input, supplied with both +5V and -5V but produces very little output. This should be the missing channel and it needs a replacement. Checked the ADPCM and audio code ROM with internet ROMs and found no corruption.
Checked the capacitors and all seems to be in okay conditions. So the noise isn’t coming from the caps. Could be 3 op-amps all being marginal, or could be coming from the Yamaha FM chip.
The repair
IC97 replaced. The missing channel is back. Other sounds are still noisy.
Replaced IC98 and IC99 with new 4558D. All sound channels are repaired.
But wait.
After the stress test, I can still find some cracking sound. Replaced C77 and C76 with Mylar 154 and electrolytic 47uF capacitors. But the cracking noise keeps going. It actually is from IC81, an OKI MSM 5205 DAC chip.
Replaced IC81 - M5205, stress tested and sound appears to be crackling noise free.
Fully repaired.