My friends PS3 was failing during the install of update 3.50 with the error code 800F1F9.
The instructions on the screen was to switch of and start again. He had contacted Sony support who said it was an issue with the game that had the update bundled with it. The game manufacturer said it was a fault with the PS3.
After a bit of research I found that the point at which the update was failing was when the update tried to write a new firmware code to the bluetooth/wifi board. Ordered a replacement board from ebay (used one was £9.00 inc postage). Fitted the board and the update completed on the first restart and all is now well.
Fitting the board is very easy (takes about 10 minutes). You need a Phillips screwdriver and a T10 security torx (available from Halfords if you don’t have one). One thing to note, try and get a board with the ribbon cable attached as it’s much easier to disconnect the ribbon from the PS3 end than than from the board.
There are plenty of youtube videos showing you how to remove the cover of a PS3.
PLEASE NOTE: To remove the cover of your PS3 you need to remove the security sticker which will void your warranty. So only do this if your warranty has expired!