Next steps would be to use an oscilloscope and check for audio at the output of the D/A convertors.
This sounds a strange problem... the fact it 'plays' and is fully functional apart from actually having audio present suggests it could be a fairly deep seated fault.
We always check the basics first which means checking all the appropriate power rails are present. At this stage that means confirming +12 and -12 volts is on pins 8 and 4 respectively of the upc4570 opamps. There should also be +5 and -5 on pins 16 and 8 of the AD1861 D/A convertors. Hard to see there could be a problem there as they are duplicated but check anyway. Any problem there could conceivably reflect back and corrupt the data applied to both convertors.
Beyond that and a scope is probably required to dig deeper into what is going on.
This sounds a strange problem... the fact it 'plays' and is fully functional apart from actually having audio present suggests it could be a fairly deep seated fault.
We always check the basics first which means checking all the appropriate power rails are present. At this stage that means confirming +12 and -12 volts is on pins 8 and 4 respectively of the upc4570 opamps. There should also be +5 and -5 on pins 16 and 8 of the AD1861 D/A convertors. Hard to see there could be a problem there as they are duplicated but check anyway. Any problem there could conceivably reflect back and corrupt the data applied to both convertors.
Beyond that and a scope is probably required to dig deeper into what is going on.
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