LCD touchscreen w/ horizontal lines

[vindoline]

I've got a piece of lab equipment with a problem touchscreen LCD. On power-up it appears to pass its self-tests, however the screen is not useable. Initially, I assumed it was a loose ribbon cable or a dirty zebra strip in need of cleaning. However, this does not appear to be the case. I've re-seated all the cables multiple times and I've checked the solder work on the ribbon cable under the microscope and it looks good. The LCD and touchscreen components are siliconed together and disassembly isn't feasible. Furthermore, it's possible to get the entire LCD to light-up white while inserting the 14-pin ribbon connector. I don't think there is damage to the LCD screen itself. I'm wondering it there's a known common failure mode that causes this. Any ideas are welcome.

[ataradov]

It is a bad connection inside the LCD. You need to undo the black bent clips, remove the board and clean or replace the zebra strips inside the LCD. It does not look like touch screen will be in a way.

[vindoline]

Thanks Alex, I'll try and take a look at this tonight.

[vindoline]

Alex, you're right that by straightening the aluminum clips the LCD can be disassembled. However, I still believe that the LCD itself is fine. With the frame off, gentle pressure or flexing has no effect on the horizontal lines in the display - however it does cause issues in the vertical direction  Additionally, the fact that I can get all pixels to light up briefly while inserting or removing the ribbon cable suggests to me that the LCD and its associated row and column driver chips (LC79401 & LC79430) are fine. I'm wondering if it could be the Epson controller (S1D13502) or its associated RAM? Any tips on how to troubleshoot this would be appreciated.

[james_s]

If you get all the pixels activated while inserting or removing the cable that suggests that there may be a problem with whatever is producing the signal. Can you find a datasheet for the display that shows what the signal should be?

[ataradov]

The cable is clearly just a parallel interface, so it looks like all pixels are activated on power cycle. This may be just some internal reaction of the LCD panel to transient voltages that happen on power up.

[james_s]

Sure but with a parallel interface it's still possible for a fault in the frame buffer to produce lines through the picture. The connection between the glass and drivers you suggested is the first thing I'd suspect though.