Falcon 2: Mechanon

From the back of the book:

The Ultimate Weapon.
The fate of Earth lies in your hands! As special agent Falcon, you have just been briefed on the alarming timeline changes emanating from the long-dead world of Mechanon. Once it had been an enormous factory-planet, where teams of robot warriors assembled a fearsome array of space weapons...until a terrible nuclear catastophe reduced it to a tangled ruin of rock and metal. Now a renegade Time Lord is using his powers to wipe out that past disaster, and make Mechanon once more the most deadly arsenal the universe has ever seen! Time is short - and only you own ingenuity in altering the course of history can save mankind from the Time Lord's ultimate weapon!