Gordon,
Thinking about your data, I came up with possible reasons for the failure and what the failure is.
Based on the scope measurement of the voltage on C201, I believe one or both D24 and D25 are open.? I base this on your measurement of around 20 volts on C201.? The values would be consistent with a rectified value of the peak voltage.
The failure would be an overvoltage on one, a short on one, then an overvoltage on the other.
73
Evan
AC9TU
