Barry OGrady wrote:

I purchased a Yaesu FTDX-400 from an online auction. I have not
attempted to test the transmitter as I lack a suitable antenna or
dummy load. However after some time listening to 40 metres
a circuit breaker in a power board popped out. I reset the CB
and there was a loud bang and a puff of smoke from the area
of the power supply. A quick look under the chassis did not show
anything obvious.

Well, get out the meter and start looking. Apt to be a bad capacitor
or a bad diode (or something else failed due to a shorted capacitor).
The meter will tell you for sure.

Your main worry is collateral damage from bad caps.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."