I send my device 3 times to the authorised HTC service center because of this problem, they cleaned it (not perfectly) and the dust was back again after few days of use. This was really ennoying for me...
After several disassemblies, cleaning, research where dust comes in, then assembles I found the flaw.
The dust doesn’t come in via sealing foam between the touch screen digitizer and LCD.
There is a bump defect of phone housing around the volume keys. Inside of the plastic housing is a metal frame, where the touch screen digitizer is stacked on - that frame is a little bended and the touch screen doesn’t stick properly on it (around the volume keys only). When you look close on the phone you can see also a little wider gap between the touch screen top glass and silver plastic housing edge. (See picture)
The following directions WILL VOID
your warranty - you are performing
this repair at your own risk.
So, now, what you have to do:
For those, who have already dust in, just simply disassembly your device (if you are brave enough, have all tools and precise hands - maybe some experience ) and remove PROPERLY all dirt with brush, compressed air and antistatic cloth, then assemble it back or send the device to the service center to clean it (wont void the warranty). Before sealing your TD2 (keep it in plastic bag away from dust) prepare a sharp wooden toothpick, neutral transparent or black silicone (you can purchase it from any building material shop) and cotton cloth.
Now you have to clean the gap between whole plastic silver housing frame and touch screen top glass with soft brush. Then use sharp wooden toothpick to impress the silicone into the gap (all gaps you can see, just in case) (silicone does not damage phone housing and TSCR surface and it’s easy to clean), then just gently and properly wipe off all the rest of silicone from phone surface. (be careful not to get silicone to the keys or phone receiver slot)
Leave the phone for several hours to get silicone dry.
Then you can use your TD2 in dusty environment and your display stays absolutely clean and dusty free. (TESTED on mine, for me perfect phone now and I am very happy with it...)
For those who have a little dust in and want to stop come more in and those who are planning to buy TD2 (dont wanna play the lottery faulty or not ), do the same procedure (silicone impress only) after unwrapping your device from plastic package.
GOOD LUCK!!! ENJOY YOUR ABSOLUTELY DUSTY FREE DEVICE!!!
Sorry for my English