Sorry for the silly question but I got this 20ohms resistor (RP2 in the schematics) in line on my primary circuit.
I am struggling to identify it. It does not appear a regular resistor. It is a thermistor?
Yes, an NTC thermistor. Note that the schematic indicates a “cold” value for RP2 resistance.
thanks for your answer.
so if it is negative it as current flows through it will increase temperature and reduce resistance. I imagine to a point where it will just be a jumper.
if that is correct i could replace it with a jumper temporarily for now just for testing purposes.
Also what is the reason for such device right out of the mains?
I believe it's to reduce the inrush current. When it gets hot, its resistance is low for normal operation.
So it starts smoothly. As i mentioned it is the fine to replace it with a jumper or maibe a fuse?
No, the part burns due to a short/overload on the SMPS primary side. If you must jumper the NTC, add a lightbulb in series and it should not stay lit. It's rare these parts burn up due to their old age.
First I would check the main switching transistor for shorts, bridge rectifier etc. Need to see more of the schematic/model number.
For temporary testing it should work to use a jumper, but if the NTC failed you'll want to make sure there isn't a short that fried it. It's there to reduce the inrush when switched on, that increases the life of the power switch and reduces the stress on the rectifier and bulk filter capacitor.
nice, thanks!!!! Will give it a go.