Philips 170S Repair

A couple of months ago a friend brought me this monitor. Each time it was switched on, the image appeared for about one second and then the screen turned black but the power LED was still on.

After browsing the web searching for a solution I found out that most of the failures were related to the backlight circuit and could be repaired by replacing the power supply capacitors. So I picked my multimeter and started testing the capacitors and the oscillation on the supply voltage. Everything looked fine.

The capacitors didn't seemed to be causing the failure. I could not find the schematic for this monitor so I started to search for causes of the failure on the circuit board.
I identified the backlight inverter controller (BIT3193G) and after reading the datasheet I found out that this IC has a protection feature that, in case of failure, can disable the PWM output after a certain period of time defined by the capacitor present on the TIMER pin.

One of the pins related with failure detection is the ISEN (pin 15), this pin senses the load current and can detect a load malfunction. If the voltage on this pin is less than 1.3V, then there is a load failure and the controller shuts down the PWM. Because this was an old monitor, the only this that I needed was to make it work, I wasn't interested in buying new lamps to test if that worked and I didn't care much with failure detection so my goal was to make the controller think that everything was alright.

It was really simple, I just connected a 220K ohm resistor to the ISEN pin and the IC supply and that did the trick. The monitor is now working and I'm testing it for the weekend.