Hello, I have a Yamaha tx802 I am trying to fix. I found while Googling my problem that there are a fair number of people who had failing power supplies that then killed the DAC, Burr-Brown PCM54HP.
My quick question is , MC74HC4051N compatible with CD74HC4051N? I think the only difference is manufacturer?
My bigger question , if anyone knows if faulty DAC can pull down the voltage so far? If I measure directly from the voltage regulator, or even at the cable connector on the power supply, i see good +15v & -15v. But, if I connect power supply to the main board, power supply still measures +15v & -15v at the connector BUT on the main board at the connector it measures +10v & -12v, despite this some components properly receive +15 / 15v. How is it possible??? Only at the DAC I see low voltages like -5 and +5v where it should be -15v and +15v. Is the DAC able to pull down the voltage at the connector?
I bought a new PCM54HP, but I think there are more problems than just the DAC IC.
I found lots of problems when I opened it up.
- All electrolytic capacitors on the power supply were leaking or bloated, and one resistor near some capacitors was broken (should be 10 ohms, showed 200 ohms and was partly exploded)
- I replaced all electrolytics and the bad resistor. Then I saw proper 5V, +15V, -15V at correct voltages from the power board.
- When i attached the power supply the main board, +15v / -15v is pulled down to +7v / -12v
- All op-amps have proper +15v / -15v, but DAC PCM54HP had +4.8v / -4.8v
- I found Two small 1uf on the +15v / -15v rails going directly to PCM54HP were shorted. When I replaced these capacitors, PCM54HP now shows +5.6v / -5.6v
- PCM54HP directly connected to a pair of MC74HC4051N, so I am worried it is broken as well