The ACP phase B converter plant was damaged by an explosion within the converter in February. No one was injured.
The company has finished repair work and started ramping up the plant, with refined platinum group metals production expected to be back to normal on May 12, when force majeure to suppliers of concentrate will be lifted.
Amplats chief executive Natascha Viljoen said: "We have safely and successfully completed the repair of the ACP Phase B unit ahead of schedule, enabling the restart of refined production of our platinum group metals and our base metals."
"We were vigilant in adhering to strict health and safety protocols to keep the repair team safe during the lockdown, whilst ensuring that we were able to implement social distancing and hygiene requirements which form our new way of working during the COVID-19 pandemic."
The company expects the cost of the repar to be about 150 million rand (US$8.2 million).
Due to the time taken to refine the respective platinum group and base metals, the force majeure notice remains in effect for Amplats' refined metal customers for the time being.