S-6 troubleshooting conditions


After successful repair of the S-52 pulse head, now I'm going to repair one S-6 that has a very distorted output waveform (I've another one, fully functional).
Before to dismantle the broken one I've read the manual and schematics.
Somewhat surprisingly, I found no troubleshooting conditions apart few lines indicating where to find a suitable the trigger signal for the test oscilloscope (from a 7S12).
Should I use a 7S12? Or the 7S11/7T11 pair? Which settings? With which input signal into the S-6 (if any)?