How to test the TDK TBD420NR CCFL inverter

TDK TBD420NR inverter with some signal paths highlighted.

The TDK TBD420NR CCFL inverter is found in many laptop screens. I've found it in an HP Pavillon DV9500.

LCD screens with CCFL backlight are prone to failures and  you are often in doubt if it is an inverter or CCFL lamps failure.
So it is very useful to have a way to live check the inverter before ordering a new one just to discover that the failure is elsewhere.
I've found a way to live check the TDK TBD420NR.

Material needed:
- cc power supply capable of 18V 3A;
- a trimmer 1Kohm;
- a multimeter (any kind);
- some wiring (of your choice); I also used a solder-less breadboard;
- a good CCFL lamp with a connector compatible with the inverter output socket.

First you need to get +4Volts out of the 18V available: connect the trimmer with external pins to +18 and GND respectively. Connect the multimeter to the central pin, turn the trimmer until you get 4volt (not critical, but no more than 5V not less than 2V) .

Connect the CCFL lamp to the inverter output socket.
To power the inverter up connect +18Volts and ground at red and blue circles respectively (see pic).
To enable it poke +4Volts to the yellow circle (it is close to the left of R14: it is the test point for the ENABLE signal).

TDK TBD420NR with connection points highlighted.

Et voilà, if the inverter is goods the lamp should lit.

Once you are sure the inverter is good you can replace the test lamp with your screen and test the backlight CCFLs as well.

Here is my fixture...

TDK TBD420NR test fixture.

Good luck with you inverter ;=))