Holding the remote horizontally, i/r window to the left (I'm right handed) with the side of the remote facing you, peak over the top and draw an imaginary line across the remote towards you from the top of the "OPT+" button. The PCB edge is very close to the points where the knives are inserted to open the casing, so be careful not too push them in too far as the board could be easily damaged. Remember that everything is carried by the upper plate (the circuit board and button rubber is lightly clipped to it); including the battery springs which should lift out of their holders as you prise the cases apart.

User’s Manual - Humax User’s Manual - Humax

Once you get these two open, the rest are relatively plain sailing. They are ALL the same, all the way round; even at the ends. Pressure on the top plate inside the gap releases them. The bottom compartment is over them. If someone is not too familiar in doing something similar I think it is worth my mentioning a couple of points.I inserted the tip of the small blade of a Swiss Army Knife into the seam that runs all around the remote 3mm from the top. I started about 90mm from the IR transmitter (between two lugs) and gently eased along the seam towards the middle of the remote, pushing out the side slightly and levering up the top, until the first lug popped out of its slot halfway along. I then carried on with this technique until all 14 lugs were popped. I found it easier to pop the end lugs after all the side lugs were freed. None broke and very little force was needed. The lugs are symmetrical each side and are positioned as follows starting from the IR end (top): 20mm, 65mm, 115mm (centre), 165mm and 210mm - each measurement to approximately the centre of the lug. There are two lugs on the bottom 15mm from each corner and two at the IR end 10mm from each corner. Your typical remote uses plastic clips molded into the body to hold the top and bottom halves together. Sometimes, you might need to push in either the top or bottom edge along the seam to help pop the clips apart. When handling the PCB be careful not to touch the board printed circuit or the on board chip with bare fingers as I would be a bit concerned that ones body static may damage the chip. I am not sure how static tolerant chips are these days; it used to be a problem some years ago, where static could destroy electronic chips. Of course if one earth’s themselves, (I do it by touching the bare steel frame of my PC that happens to have the cover off), then there is no problem.

RM Series Replacement Remote Control for HUMAX RM-F01 RM Series Replacement Remote Control for HUMAX RM-F01

So it's not the remote. Thanks just tried it again - yes my HD remote does use the 4 digit codes - you have to press OK after each code to then test it - it doesn't send a power off after entering the 4 digits as stated in the manual which makes it slower to find the correct code. Start in the middle and work carefully upwards and downwards. Press and hold the 0 and OK buttons simultaneously for 5 seconds until the PVR button on the remote stays red. Many thanks to Barry & Martin Liddle for their tips and links as below, as now I have a fully working RM-F01 remote control once again. I first removed the batteries for safety. The top and bottom are totally separate (no wires) when they come apart. There were no screws holding this remote together Find yourself a small very thin penknife blade (I used a Swiss Army Knife one - the smallest blade)

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Once all the lugs were popped the keyboard complete with circuit-board lifts off the housing and there are no connecting wires. To remove the circuit board there are 4 plastic lugs. I eased the board from underneath the bottom two (one at a time) and it came easily away from the top two. The buttons are all on a single rubber sheet which lifts off and can be cleaned by washing in warm water with a drop of fairy liquid. Rinse thoroughly in clean water (preferably de-ionised) and thoroughly dry before re-assembly. Ensure the loop of springy wire connecting the batteries is still in place in the housing before re-assembly. It is easier to engage the top and bottom lugs before the side lugs are clipped as there is more give in the sides.