The power entry module receives AC power from the mains supply and converts it to lower voltage DC power that the CPAP machine needs to work.
To check that the power entry module is working correctly, you should have the CPAP machine disconnected at the wall and the top cover open.
Use a number 8 socket spanner to unscrew the nut from each of the bolts.
You can then lift the module and rotate it to access the electrical circuits.
First, check for any loose wires and re-attach them securely. This may solve the problem. Also, check for obvious signs of damage, such as burned or melted components. If you find damage, you’ll need to repair or replace the power entry module.
Next, check that the module is receiving power at the correct voltage.
You’ll need to plug the CPAP on at the wall for this test. There will be live power in the machine so you’ll need to work very carefully.
Set your multimeter to AC voltage. At the power input connector, insert the red probe into the slot with the brown live wire. Insert the black probe into the slot with the blue neutral wire.
The multimeter should show an AC voltage reading that matches your country’s mains voltage – in this case around 220 volts.
Next, test that the power supply unit is outputting power at the right voltage.
This time, you’ll need to set your multimeter to DC voltage.
WIth the CPAP machine plugged in and switched on, carefully replace the red probe into one of the terminals with a red wire and the black probe into a terminal with a black wire.
You should get a reading of around 24 volts.
Repeat this in turn for each red wire with each black wire.
If you don’t get this reading for any of these tests, there is a problem with the power supply unit and it will need to be replaced.
Next, test that the correct power is going to the alarm control board.
Your multimeter will again need to be set to DC voltage.
With the CPAP switched on at the wall and on at the machine, place the red probe against one of the output wires that lines up with a red live wire. Place the black probe against one of the wires that lines up with a black neutral wire.
You should get a reading of around 24 volts.
Repeat this in turn for each red wire with each black wire.
If you don’t get the expected reading on your multimeter, for any of these tests, there is a problem with the power supply unit and it should be replaced.
If any of these tests showed that the power supply unit is damaged and has to be replaced, you’ll need to detach it from the CPAP machine.
Take a photo or make a note of where each of the wires connects.
With the CPAP power off, connect the new power supply unit in the same way as the old one. Turn on the machine and check that it is now working.
