Howdy Ray.....I don't know your radio specifically but would suggest
initially determining whether you are looking at a bad power circuit
connection which fails under transmit load OR whether there's an
abnormal heavy current condition occurring during transmit. Does the
receiver otherwise work ok? One place you might look is at any
switching contacts part of a connector for external power or for
external charging. I've found many times particularly with the coaxial
type power connectors that when they use a contact to disconnect the
radio during charging, that this will fail under load.

You didn't mention whether you experienced a heavy current condition
while testing with your bench supply so I tend to think the situation is
a poor connection. IF it seems that you're into a heavy current
condition during transmit, you might check for a shorted
stage....disconnect power at the final for example to isolate that and
work backwards.

Hope this helps get you started.

Gord VE1AJF