Urgent! Need Help! Flashing monitor

**tonkadawg** · 02-13-2008, 01:11 PM

Originally Posted by bbalazs

Once I repaired a small TFT, where the two main GND parts on the PCB was totally separated and connected via the aluminium backplane by screws. And because the customer removed that, there was no picture.

yeah but I am getting a picture. It's just that sometimes it flashes on and off, while other times its fine.

**tonkadawg** · 02-14-2008, 01:51 PM

Originally Posted by bbalazs

I am not sure, but the source of the problem can be a backlight problem.
The system enables backlight, but it consumes too much current.

Set the backlight off. Make a picture with good contrast. Enlight the display with a strong lamp. Can you see anything on the screen (of course very faded)? If the picture stands and does not flash, I won and backlight unit is guilty

If the pale picture also flashes, I am afraid you have to search problem around the voltages on the PCB.

Methods to set backlight off:

If the backlight unit is separated, de-connect it at the low-voltage connector. If it is not separated, solder the backlight fuse out.
The backlight unit is, where that small transformer is located and those teflone-insulated cables (usually pink and white) are connected.

Can someone expand on this? I'm not to familiar with LCD TS internals. What is the backlight unit? There is a board that has one pink/white cable and a blue/white cable plugged into it - is that what we're talking about here?

**tonkadawg** · 02-14-2008, 05:09 PM

another interesting note that maybe someone knows the cause. On the way home from work, screen was blinking like normal. After about 30 minutes it finally settles down and stops. After that, I decided to try adjusting the resolution and refresh rate. Set resolution to 800x600 and my only choice for refresh rate was 60Hz. Anyways as soon as I set the resolution, the screen starts flashing again. Coincidence?

**Morpheus2010** · 02-14-2008, 06:57 PM

I'm about to take a picture of the back of my shark 8" monitor so bbalazs can tell me which exact wire i need to do what ever to.

**bbalazs** · 02-15-2008, 05:44 AM

The backlight unit is a part of the display, that is TOTALLY independent of the part that is responsible for the picture. It is wired with power, GND, enable, dim. This unit contains some electronics (usually a controller IC) and switching elements, usually transistors of FETs and a transformer, that produces the high voltage needed by CCFL or CCFT (cold cathode fluorescent tube/lamp - the same thing!). That voltage is approx. 1500V at ignition and about 800V during operation. The primary part has an overcurrent protection, and very likely this is the cause of flashing.

When one changes resolution, the enable is inhibited for a short time, therefore the flashing could start again.

If you are not familiar this things, I suppose to see the service.

**tonkadawg** · 02-15-2008, 08:25 AM

ok so I'm pretty sure I know that part your talking about, but if Morpheus is gonna post up a picture, I'll hang on so I know what I'm doing is 100% right.