Circuit boards for Davey Spa-Quip Spa Power 500 spa controllers. There is a difference in wiring looms and incoming power connection between the 2 versions. Also the 500A has a manual reset hi-limit that this new mk2 version pcb does not. 

There 

• Old Style suits: Spa Power 500, 500A, Spa Power 54500, 54500a. These are no longer available. You will need to purchase the upgrade kit here. 
  This includes: 54500-15, 54500-20, 500A15, 500A20

• New Style Suits: Spa Power 500A Mk II pcb for all Spa Power 500A Mk 2 SP500 controllers. Does NOT suit first release 500A circuit board replacement above.
  This Includes: SP500A15MK2 and SP500A20MK2

Other SP500 / 54500 Parts:

• Heater Element: 1.5kw / 2.0kW
• PCB Upgrade / MK2 PCB Standalone
• Body O-ring
  
• Locking Ring
• Union O-rings
• Barrel Unions
• Touchpad: Oval / Rectangular
• Controller Unit - Complete (no touchpad)
• Complete Control System
• Optical Sensor: Type 1 / Type 2 (9.22mm OD) / Type 3 (11mm OD)
• Element Carrier (500A only)