Ok So Mac has been helping me over at Repairalmostanything.com.
We did some test and I'll repost it here.
He had me remove TR107,103,and105 and test the voltages on either side of R115 and R116 this is what I got
R115 -11.09 and -4.9
R116 +4.04 and +189.3 mV
the +/- 4 voltages are on the transistor side of TR103,104
the mV readings are probably just my meter we think.
So then he had me remove TR108,104 and 106 and retest the voltages on R116
I got
-6.96( goes to TR104) and -13.7
So then he gave me more voltages to check.
"Looks like they are pretty close to even. Now more voltages to try to narrow this down. Leave all parts removed for now.
Gate of tr107 on 103 side_________5.4 mV
Gate of tr107 on 105 side_________-2.7V
collector of 103______24.87
collector of 105______24.76
Gate of tr108 on 104 side______7.3mV
Gate of tr108 on 106 side______-1.7V but it drops steadily stoped measuring at -1.5
collector of 104_____25.08
collector of 106_____25"
So after this he had me :
"I just want you to put in the tr103,105,104,106. Swap channels though and then do voltage test again. BEC of all 4 and the 2 gate pads for 107 and 108 on the power side. This time, before you plug it in to test I want you to rotate the "Phono Selector" knob back and forth a bunch of times to try cleaning the contacts and then leave it on the 47K setting and then test voltages."
Here is what I got:
TR103
E=0 , C=24.64, B=-7.04
TR105
E=0, C=24.80, B=-7.04
TR104
E=0, C=25.12, B=-7.02
TR105
E=0, C=24.9, B=-7.03
TR107
G=-2.081
TR108
G=-1.452
They seem close
So now I am waiting on some cheaper Jfet's the 2SK363 single's to test . I wanted to Match them but for testing I guess it doesn't matter.
Macs Advice:
Matching them is not important for now. We are more concerned about how the channel reacts with them installed and hope the problem is resolved.
As far as the voltages matching now, well this is the first time we tested this way. Each part seems to affect the voltages.
And each part is required to balance the + and - line voltages. Everything is artfully placed to achieve a balance of 1 voltage against the other.
We also don't know for sure if the phono selector switch was causing an issue. That alone could of been the problem for blowing that TR107.
And since that FET is tied directly to that phono selector switch I would not recommend changing it with the unit powered up.
I would shut it down for a minute before changing that selector. FET's are very sensitive and a spike when changing
that selector could cause a failure.
Read more:
http://repairalmostanything.com/thread/491/yamaha-960?page=3#ixzz4Q6Dc5nI2
So this is where I stand. Weird how just swiping the parts to another channel got me different voltages as I have removed those parts a few times
so I know its not bad solder joints. Hmm a mystery. I ordered 8 of the JFet's , 1.40 each compared to 15 for the 2SK146 dual units!!!
Hopefully the circuit will be ok when they are installed.
Thanks Mac so far !!!
Athanasios