Suburban circuit board is on backside of water heater
Suburban has a 3/4" drain hole and uses an anode rod
Suburban combustion chamber is on lower right side and the exhaust is directly above it (Stacked Chamber)
Suburban Gas Only WH
Atwood circuit board is in outside compartment above combustion chamber
Atwood has a 1/2" drain hole....no anode rod.......uses a nylon drain plug
Atwood combustion camber is on lower right side BUT exhaust is on top left side (Diagonal Chamber)
Atwood Gas Only WH
Dinosaur Electronics has replacement Circuit Boards (water heaters, furnaces, fridges etc)
If you have a number on current board they can cross reference.
Otherwise you can use a 'universal board'
http://dinosaurelectronics.com/Ignitor_boards.htm