With the CPAP machine open, carefully pull up the protective foam that covers the variable synchronised unit.

Undo the two long screws attaching the top and bottom parts of the unit. You will need a star-headed T25 screwdriver. Do this slowly to avoid damage.

You can then lift off the top part of the unit.

Next, we will release the four hoses. Use a flat-headed screwdriver to undo the screws attaching the hose clips. There are four screws to undo, one on each side and two at the back.

You will then be able to detach each of the hoses from the unit. You might need to use a flat-headed screwdriver to help work them off.

First, let’s look at the top part of the variable synchronized unit. When dirt builds up here, it can stop the motor from working properly.

Remove the small gears from the casing.

You may need to clean out the chamber to remove dust, debris, and carbon deposits. Use a clean, dry cotton bud. It is important not to use water here as it could get into the motor and damage it.

Check that the rotor is spinning freely by twisting it with your hand.

Lift out the black O-ring and check it for signs of wear and damage. If necessary, replace it with a new one.

The O-ring may be intact but require cleaning. If so, use a damp lint-free cloth. Let it dry completely. You then need to reapply a lubricant. It is important that this is the correct type of lubricant as guided by the manual.

Carefully sit the O-ring back into its position in the chamber.

Next, check all of the gears for signs of wear. If they are all worn, you will need to replace them.

Next, we will look at the valve section at the bottom of the unit. Dust and debris can affect the operation of this part; cleaning it can help to make it run optimally.

First, make sure the white variable plate is rotated in a way that the holes are not aligned. If the holes line up like this, dirt can get inside the chamber and is very hard to remove.

Carefully clean around the white variable plate with a dry cotton bud or lint-free cloth, then continue to clean the rest of the outside of the chamber around the sides and base.

Before you reassemble the unit, the variable plate needs to be rotated to the correct position. The metal stud should be lined up with the circle below, as shown here.

Next, place the gears back in place. It is easiest to press gears into the motor gear so that the teeth are connected correctly. Place the black gears in with the lugs facing outwards.

Put the gears opposite one another so they correspond with the holes on the plate.

Now you can place the two sides of the variable synchronized unit back together. Be careful to keep the loose gears in place and ensure they are aligned inside.

Turn the top piece to test that it is working properly.

Next, make sure the top part of the assembly is turned the right way in relation to the valve ports. The wire plug socket here should face the same way as this hose port.

Also, check that the small circuit board will be in the right position, but don’t secure it yet.

Place the long screws back into position, then carefully tighten the screws back into place using your T25 screwdriver.

Now, position the small circuit board back and screw it into place. Use a T15 screwdriver.

Plug the bundles of wires back into the circuit board and the motor at the top.

Now, place the variable synchronized unit back into position in the machine.

Next, reattach the four hoses using a flat-headed screwdriver or a number seven spanner to fasten the clips.

First, attach the two hoses coming through the back. Then, attach the first side hose. Finally, secure the hose on the other side.

Next, you will need to reattach the bundle of coloured wires to the circuit board. Pass the wires through the cable ties and plug them back into the circuit board.

You can then reassemble the CPAP machine, turn it on, and test it.