I am not sure Martin is on the forums atm? so contact him via PM. Just to add to above I always add a dil socket so I do not need to solder the replacement IC in place AND the reason this IC fails in my opinion is that it is placed right next to the big transistor used as a voltage reg. This kicks out quite a bit of heat and can sometimes be found touching the IC! Move as far away as you can without removing and angle up but make sure the tab does not touch anything including the metal lid when placed back!
To get to the IC one must remove the keypad 3 clips under the front edge (undo two bolts, lift rear pull top part forward to access underside - see service manual) then the keypad slides forward and lifts out. BE CAREFULL as the three top clips can easily break! This will give access to the metal can with micro circuits. The lid can be carefully levered off and will reveal the IC. Lift the top (Like a car hood) to gain access to the rear of the board. Must be very careful and gental with everything in this area and take anti-static precautions!
Martin will also supply a belt and I am sure instructions this can be done at the same time.
BTW I agree above in as much as those two electrolytic capacitors will be worth doing and a trimmer that can be sensitive to disturbance but before replacing the latter, make sure you have read the setup proceedure, have the relavent equipment (PSU meter etc) and are sure you feel comfortable attempting otherwise leave well alone!!!