Found an old NAD T760 which needed a little TLC, clean it up, straighten the case etc. The only issue it had was a hum in the rear channels.
Initially using the optical input the noise was horrendous but calmed down after a few minutes but was still quite audible. If you just use the analog inputs things improve in all channels and if you use the pre-out RCA connectors the sound is again clean.
This led me to the belief the hum must be isolated to the surround board and changing the caps to newer ones would clean up the signal, so fitted some Elna Silmic II. I double checked the connections after I did each one and validated the caps were the same way round as before.
Put everything back together and while the rear channels sounds better the original hum is worse than before, not horrendous and when you watch a film it isn't very noticiable but I would like to resolve the issue if I can.
A visual inspection of the board looks fine and when I plugged it back in nothing I could reach got hot nor did the heatsink the transistors are attached to.
I do have some initial thoughts but would really appreciate any suggestions on what I could do to resolve this. I am no expert, not even at an intermediate level but I am trying to learn and happy to have a go.
A few thoughts I had:
Wondered it a shielded power supply would help.
The board has empty junction connectors marked A and B thought of connecting them with a separate wire
Could there be interference from the power supply which is right next to the board
Could there be interference from the AC3 board which has a random wire running to the surround board. NB. There are a few extra wires connecting boards together which I think is factory as I saw this in pictures of another T760 just a bit bizarre.
As I said, your suggestions would be appreciated
Initially using the optical input the noise was horrendous but calmed down after a few minutes but was still quite audible. If you just use the analog inputs things improve in all channels and if you use the pre-out RCA connectors the sound is again clean.
This led me to the belief the hum must be isolated to the surround board and changing the caps to newer ones would clean up the signal, so fitted some Elna Silmic II. I double checked the connections after I did each one and validated the caps were the same way round as before.
Put everything back together and while the rear channels sounds better the original hum is worse than before, not horrendous and when you watch a film it isn't very noticiable but I would like to resolve the issue if I can.
A visual inspection of the board looks fine and when I plugged it back in nothing I could reach got hot nor did the heatsink the transistors are attached to.
I do have some initial thoughts but would really appreciate any suggestions on what I could do to resolve this. I am no expert, not even at an intermediate level but I am trying to learn and happy to have a go.
A few thoughts I had:
Wondered it a shielded power supply would help.
The board has empty junction connectors marked A and B thought of connecting them with a separate wire
Could there be interference from the power supply which is right next to the board
Could there be interference from the AC3 board which has a random wire running to the surround board. NB. There are a few extra wires connecting boards together which I think is factory as I saw this in pictures of another T760 just a bit bizarre.
As I said, your suggestions would be appreciated