Yes, what Ludwig recommends is important.? A failed Q508 could be the cause of the problems, with D516 being the trigger.
Here is one theory of what happened:
a) With D516 either not connected, or worse, intermittently connected, all of the rapid tx/rx cycles during calibration stressed Q508 until it broke (likely shorted D-S).? [Perhaps this broke IC402, also, since failures there were the reason D516 was added.]
b) With a shorted (always on) Q508, there is an unexpected load during transmit put on the output of T501 and hence the PA transistors; akin to having a high swr.? They responded by failing during the full power parts of the calibration.
c) Failed PA transistors can overload Q507 and/or IC503, causing one or both of those to fail.? We can hope that didn't happen.
?
So do check Q508 before powering up with new PA transistors.
?
This failure theory would have happened independently of firmware if you operated CW with its full break-in, over perhaps an extended period; or at least doing so would have stressed Q508 such that it broke during calibration.
?
Stan KC7XE
