DIYbanter - View Single Post - Power supply problem on touchscreen contoller

Jon Elson[_3_]

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