This repair is complicated by two main factors:
1. It involves removing the main PCB out because IC1508 located on the underside of the board.
2. IC1508 is a surface mount component (an SMD).
Disassembly
In reality, removing the main PCB isn't too bad. The service guide gives details, but in summary:
1a. Remove the top cover (three screws on the rear, one on each side).
1b. Remove the front panel (two plastic tabs at the side and three underneath. Careful you don't break them!)
1c. Remove the HDMI output board. The ribbon cable goes into the digital PC on a simple push fit connector. Gentle pulling removes it (when replacing ensure it is parallel).
1d. Remove the SD card board. Two screws and another ribbon cable.
1e. Remove the rear panel (5 self tapping screws, including the one already removed for the HDMI board, plus two smaller machine screws). Leave the fan screws in place and instead disconnect the fan cable from the power PCB. There are two metal lugs holding the rear panel in place - one on each side.
1f. Remove the power PCB. Gently pull the power rail connector (it's quite stiff) from the power PCB and remove the 3 screws. Remember, there may be some nasty voltages still lurking!
1g. Remove the hard disc drive (HDD). Detach the HDD power cable from the main PCB and remove the four mounting screws that go through the main PCB.
1h. Remove the Digital board (that's the main green board to the left of the HDD). I didn't remove it completely. I detached the ribbon cable that goes to the HDD, removed the screws (mine only had three out of four present). I then pulled it up very gently from the rear (it has two multiway connectors on the underside). When free, I gently flipped it over onto the DVD drive so I didn't have to remove the other three ribbon cables.
1i. Remove the digital input board (one screw).
1j. Remove the digital board support frame. This is a bit fiddly. One of the screws is shared with the DVD drive and when this is screw is removed, the frame has to be pulled gently from beneath the DVD drive holder.
1k. Remove the power button PCB. This long thin PCB is attached to the main PCB by a soldered wire (don't unsolder it). Carefully remove the screw and slide the PCB on the metal lugs to free it. See picture at step 1i.
1l. I left the other components (the tuner module etc) attached to the main board. The main board is removed by undoing the remaining screws (there is a 'hidden' screw running horizontally just under the front panel phono sockets - see pic below).
1m. Remove the PCB and gently turn over onto a suitable surface (I used an antistatic mat).