smurfer77
Super Member
Hi folks,
This is my first post in the Yammy forum; I'm using found lurking over in the Exclusively Sansui forum.... but here we are .
Here is a pic of the unit that I recently obtained being desecrated by a Sansui brochure (my Sansui AU-777A in background).
Okay, so the situation is that I have good sound on one channel but on the other I have nothing (well, almost nothing). I slid the unit out of the wood case (not that easy!) and then I can see someone has worked in here before. A 68ohm resistor has been replaced by two resistors adding up to 60ohm, for example. One of the TO3 socket pins was touching, but not soldered to the board. Fixed that up. Also replaced output transistors on the good channel (some old toshiba in there but previous tech put on-semi on the other side, so I tested those and matched up on both sides).
Got no bias across that bad channel outputs and can see B+/B- are okay. Base of the output transistors is sitting at 0V. Voltages rediculous at driver transistors (some huge value sitting on the Base). The voltages coming from "S" and "C" which are meant to be 3.9V and 1.15V are something more like -30V each (just on the bad channel amp board, other board is okay).
And now I'm off to bed and will tackle it tomorrow. I know nothing about these Yamaha units so would be very grateful to pick the brains of the resident experts and says my time and wits. I guess my plan if I don't get advice is to check out that Operation (A/AB) relay in the morning first and think about what on the front half of the main boards can pull that +ve rail down. Maybe someone has seen this before?
Thanks in advance and it's great to say hello to the yammy fans at last!
This is my first post in the Yammy forum; I'm using found lurking over in the Exclusively Sansui forum.... but here we are .
Here is a pic of the unit that I recently obtained being desecrated by a Sansui brochure (my Sansui AU-777A in background).
Okay, so the situation is that I have good sound on one channel but on the other I have nothing (well, almost nothing). I slid the unit out of the wood case (not that easy!) and then I can see someone has worked in here before. A 68ohm resistor has been replaced by two resistors adding up to 60ohm, for example. One of the TO3 socket pins was touching, but not soldered to the board. Fixed that up. Also replaced output transistors on the good channel (some old toshiba in there but previous tech put on-semi on the other side, so I tested those and matched up on both sides).
Got no bias across that bad channel outputs and can see B+/B- are okay. Base of the output transistors is sitting at 0V. Voltages rediculous at driver transistors (some huge value sitting on the Base). The voltages coming from "S" and "C" which are meant to be 3.9V and 1.15V are something more like -30V each (just on the bad channel amp board, other board is okay).
And now I'm off to bed and will tackle it tomorrow. I know nothing about these Yamaha units so would be very grateful to pick the brains of the resident experts and says my time and wits. I guess my plan if I don't get advice is to check out that Operation (A/AB) relay in the morning first and think about what on the front half of the main boards can pull that +ve rail down. Maybe someone has seen this before?
Thanks in advance and it's great to say hello to the yammy fans at last!