8'' TS 2 weeks old almost dead

lez · 08-14-2007, 10:25 AM

Ok the TS has gone funny.......

Its ok if the USB cable for touch is not connected, but once plugged in, causes noise on the picture, and the touch function does not work, touching the screen causes more noise bars.

Sometimes after a minute or so, it starts to work, but it can then again fail.

If the USB cable is not plugged into the carPC but instead plugged into a laptop (so effectively the touchscreen has independent power) then no noise appears on screen, so its not an internal short in the touch screen.

This is not an earth loop, dont even suggest it, I can connect all 3 lines of the USB, it only fails when the 5v line is connected......

The voltage at the hub its plugged into drops from 4.9v to 4.5v when the fault is apparent.

The hub/power supply is not overloaded with devices, it can do this if its the only device, its as though the touch screen controller is drawing an excessive amount of current (not yet measured, will do later...)

This screen has not been opened or violated, so has warranty intact and I may have to return it, but thats a chore...

youtube vid.

you can see plugging in the USB cable causes an increase in brightness, and touching screen causes ''issues''

http://www.youtube.com/watch?v=QI6c3GJMoU0

dupa2 · 08-14-2007, 08:40 PM

the cable may be crap*y, if you use separate usb cable it should not affect video. Typically usb controller for TS is completely separated circuit, and it's powered from usb port. The controller may get overheated too, that would explain failures.

lez · 08-15-2007, 03:14 AM

Ok glad you in agreement that its separate from visual side of things, which backs up my theory that its putting heavy drain on the 5v supply from my mb/psu.

now that the rain seems to have stopped (at least it looks like it will for a few hours) I'll go out and see if I can measure its current drain on the supply, but I dont know what to expect, I cant see why something like a little custom chip, measuring resistance between a plastic sheet, and pumping out the data, should need more than a few mA, but I suppose could be as high as a hundred.