Falcon DSO-025C1 display problem

[vish2207]

I have Falcon DSO-025C1 with 25 MHz Bandwidth 2 channel. It doesn't show anything on the display.

It was working in very fine accept one problem, the brightness on the LCD was randomly varying when just touching the preset of the brightness on the front panel.

I am talking about the brightness preset shown in one of the DSO_OFF.jpg attached here on mid bottom horizontal right beside the label of company and model number.

One of the image attached shows the DSO when it is on. It just shows some light purple screen and nothing else. Even changing the brightness preset doesn't affect.

I tried to verify the operation of the DSO by connecting probe to test pin on the DSO itself which gives 5V 1KHz square wave output and pressed AUTOSET button. I can here some relays are switchin inside, so it seems it is working but there is nothing on the display.

How should I debug? Which section of the DSO should I probe first to look for problems?