The 'D' probably means you have a 'dual common' controller. You'd have a 'calendar wheel' with two pin positions for each day, one for shrubs, and one for lawn. The two common wires get connected to the valves in accordance to the use and schedule. This was a sort of mechanical shortcut to what can be done quite easily with a solid-state controller.
In simple terms, the old controller may not be cost-effective to repair. If your sprinkler system used Imperial brass zone valves, a standard solid-state controller might not supply the amount of current the valves require. Something heavy-duty like A Hunter ICC would then be needed.
If you are mechanically inclined, you can figure out how to fix the controller on your own, since it does use obtainable parts. (Imperial is long out of business) You might also find a service you can send the controller to, and have it repaired and returned.
Do note what has been said - this controller is running 120 volt circuitry, and is hazardous to monkey around with. While this made it particularly resistant to power-surge-damage, it also made it something to be cautious about.