A very common fault in the R-390 radio is failure of the selenium rectifier CR801. This is situated just under the power transformer on the power supply sub assembly. Symptoms are non operation of the antenna relay and the break-in system. To replace this is easy but there are a couple of wrinkles.
I replace CR801 with a bridge rectifier obtainable from Radio Shack, part number 276-1173. This has a mounting hole which bolts conveniently in the bracket which supported CR801.
Click here and you will find a wiring diagram of the power supply.

 CR801.gif

You will note there are five connections to CR801 whereas there are only four to the bridge. There are two wires connecting to pin 5. One connects to pin 1. Remove this and discard. The remaining wire is the positive DC lead. The wire connecting to pin 3 is the the negative DC lead. Pins 2 and 4 are AC in.
Solder these leads to the appropriate terminals of the bridge.