On Tuesday, November 27, 2012 6:39:50 AM UTC+8, Jon Elson wrote:
wrote:



I have an old IRIS 4d/35 system with touchscreen capabilities and display

is CRT type.



Recently we upgraded the system to run on LCD displays where we needed to

provide the touchscreen controller with a separate power supply since the

power for the controller was previously drawn from the CRT power supply.



However when a new switching power supply was used the touchscreen did

not work. Reverting back to the supply from the CRT works flawlessly.



Are you saying the touchscreen placed on the LCD panel works

fine when powered by the old power supply? If so, then that eliminates

the LCD drive signals as a concern for fouling up the signals on the

touch panel. CRTs have some noise on the front, but the shadow mask

generally isolates the front from a lot of noise. LCDs are REALLY

noisy beasts, with 50V pulses on a zillion "wires" on the front

of the panel.



But, assuming it really is only the power supply that is different, then

it is either the power-up sequence or noise. Possibly the new supply

voltages come up in a different sequence than the old one, or there

is noise on one or more of the voltages.



Jon

Will check on the sequence on power up, thanks Jon.