Go to Charlie Comics and give him star screwdriver, you'll receive flat blade screwdriver. Give to Vader the soldering iron and some tin and the screwdriver. The space nerd says he needs a couple of battery.
Back to the shop and talk with Charlie. Take the star screwdriver.
Use it with lightsaber, take batteries and give it to Vader. He won't give you the radio until you get him the lightsaber. Give him the one you have, but he doesn't like the color.
Pick up a lightsaber handle, combine it with laser and plutonium rod (in this sequence). Give the sword to nerd. Randal will get back the radio.