The repair guides from GHD-Repair, can be found by clicking the links below. Use a multi-meter to check for open circuit and resistance on suspected failed components. In addition, if you use this link and select a specific spare/part, there are guides related to fitting that part. There are also many YouTube videos on how to make repairs.

Mk3 (3.1B, GHD3, SS, SS2, MS etc)

Mk4 (4.0B, 4.2B, SS4.0, MS4.0 etc)

Mk5 Gold Series (MS5, SS5, Mk5, SC5 Contour)

Mk6 Eclipse (mains cable only)

Mk6 Eclipse (mains cable only), link to parts

S8T262 Platinum. No repair guide for this, but a repair service is available here

S7N261 GHD Gold & S7N421 Max. Note only the mains cable is DIY repairable, but there is also a fixed price repair service available here