1.? ?Series diodes D20, D21 can be immediately damaged by an errant scope probe/VOM probe that "grounds" their far ends, since the near ends are connected to a +12(nominal) supply.? ? In my case, the diodes failed "shorted" (melted) and as a result the T/R HV RF-derived supply was unable to properly switch the low pass filters, resulting in very large spurious outputs.? ?Adding a resistor of roughly 470 ohms in series with those diodes (before, in the middle, after, are all equivalent) will prevent them being damaged by an accidental grounding.
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2.? Small MOSFET Q101 can be irreparably damaged if it and large MOSFET Q9 are transiently ON simultaneously.? ?This depends on so many factors that it is difficult to predict the occurrence, as the individual gate-Id characteristics of each transistor will change with temperature, etc...and are slewed by Q10/R6 during every transition from Transmit to Receive etc.? ?Failure is likely in the long run if the individual device characteristics interact poorly.? ? I'm not quite certain of the consequences in individual transmitters, but suggest preventing the failure by adding roughly 150 ohms in series with the Drain of Q101.??
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