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Old 01-02-2019, 01:37 AM   #1
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Join Date: Oct 2007
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Default Dell 2408WFPb: faulty TCon or main board?

The previous owner gave me this broken monitor, saying "the picture is distorted".

They shipped it to me by courier, during which time it was probably kept in a cold warehouse.

On arrival I plugged it in and it worked fine on VGA and HDMI. I noted that when no signal is applied, the monitor cycles between solid colours: red, green, blue, black, white.

I forgot about it for a while. Next time I plugged it in was a different story. The on-screen display was extremely distorted. It just looked like noise, and after a few seconds it disappeared completely.

The colour cycling still works, and the backlight turn on and off at the appropriate times. The controls still work and I am able to switch inputs, although it is difficult without seeing the OSD.

When a VGA signal is connected I see a constant solid white screen. When HDMI is connected it is solid orange. Brightness control doesn't appear to have any effect.

The power board is supplying 23V as expected. There is nothing unusual looking on the PCBs. I can supply pictures if you want but it looks exactly like all the others that people have posted.

I connected my laptop on VGA with display mirroring and sent a full screen alternating black and white picture. I was able to scope it from the connector into what I presume is the video digitizer/scaler (the smaller of the two chips with heat sinks), and from there out into the RAM chips (presumably a video FIFO).

When I scope the LVDS signal during no-signal colour cycling I can see the signal changing, but with my black and white test signal the LVDS signals appear constant. So it seems that the TCon is displaying what it is being sent, and the problem is with the main board.

The main board is not really worth replacing for what the monitor is worth. The TCon is only like $5 though. Is it worth trying to replace that?

Any other ideas what could be wrong? Unfortunately I don't have cold spray to test if that revives it.
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