I get about 27.2V differential at bases of Q130 and Q140, and about the same
between positive and negative peaks at J135 and J145. Well short of the ~30V
needed.
With TD BIAS at mid point and assuming a linear pot, swing at Q120/125 should be about 20V*(11.1k // 30k)/(2.2k+11.2k//30k)=15.7V single ended but your scope shot shows ~ 13V. Low point is ~ 0V so the issue seems to be at peaks.
If you short TP11 to ground, do you see +17V/-17V at collectors of Q120/125 with max TD BIAS?
1) Is it possible +20V/-20V is sinking to a lower voltage during trigger time?
2) Is base of Q125 at ~ -0.7V
3) is it possible resistors R121 and R129 drifted to higher values?
There are not many possibilities around this part of the circuit, next would be to suspect the transistors. TD could still be bad but without this section working even a good TD won't function.
Ozan
