Okay, so what I'm getting is that the radio transmits as soon as you power it up, and won't allow you to receive at all.
When the computer thinks the mike is keyed, it disables the tuning controls, so you can't change frequency. If it's stuck in transmit mode, you'll be stuck on that frequency.
The way to tell is at the bottom-right corner of the orange LCD display window. A small square outline with the letters "TX" inside it.
This tells you that the computer thinks that you have keyed the mike. So long as it's visible, the computer will, in turn key the radio.
That's how this one is wired. The mike keys the computer. If the computer thinks it's okay, it will then activate an output from the computer board to the radio that actually puts the transmitter on the air. The mike only triggers the computer. The computer keys the radio's transmit/receive switching circuit.
As a general rule, when I see this fault it's because someone found a way to feed more than 5 Volts into pin 3 of the mike socket. Could be someone got frustrated trying to make the built-in linear key properly and hooked up a 12-Volt relay to pin 3 of the mike socket.
Could be that someone wanted an accessory relay to key a ham-type linear without having to use a foot switch. Looks easy. Just connect one side of the relay coil to the main 13.8-Volt power, the other end to pin 3 of the mike socket.
Bad juju.
Whatever the reason, anything that causes more than about five and a half Volts to appear on pin 3 of the mike socket *WILL* assassinate the computer.
5-Volt computer chips are famously sensitive to any voltage higher than that.
You could plug in the wires behind the mike socket wrong, and make it key up, I suppose. Can't think of any other fault besides a blown CPU that does this.
And if the "TX" in the lower-right corner of the LCD display goes away when you unplug the mike, this isn't what's wrong.
73
