My casio eletronic drums ld80 turns on and off if i started playing it specially when i hit the pad simultaneously. can you help? thanks!

Most likely he crosstalk setting to high

I would check your fingering... You MAY be late in hitting a particular note and the using auto chord... this can cause the problem. Another thing is if notes are hit with different velocity that can affect the sound. Sometimes certain voices have VELOCITY switching which actually changes the voice depending on the velocity you hit a note.

A couple of things to check:
Make sure you have a SOLID surface to place the unit since if the surface bounces it may false trigger another pad. See if there is a sensitivity adjustment... sometimes they have setting for playing with hands or with sticks, The sticks one is less sensitive and less subject to false triggering.

Your gaib control on the module or even the amp may be way down.

There is a setting for playing with hands vs sticks. Make sure to use the appropriate setting as one is much more sensitive and may cross-couple.

Your Xtalk filter is set too low. Refer to the owners manual for how to adjust individual triggers' sensitivity to "cross-talk" (vibrations carried from other pads)
My bet is you unplugged the crash trigger, but not the cable from the actual module (the brain). If you have a cable connected to the brain but not to a trigger, than any little bump to the end of the cable that isn't connected can be picked up as though you hit the pad normally. (play with the end of the cable a little, you'll see what I mean. It's kind of neat.)

http://www.yamaha.co.jp/manual/english/result.php?div_code=emi
This should link to owners manual..Hope this helps.

If you are comfortable with working on it and the warrantee is up try taking the pad apart to see if the piezo element has come loose from its mounting or if the solder joint is loose. If that isn't the problem save your settings and initialize the set according to the instructions in your manual.

hi,
the right crash is a '3 zone pad' (notice the semi-circular groove around the front edge of the pad).

this means you should get a different sound from the bell, the main area of the pad, and the front edge.

In order to mimic a real crash cymbal, the 'crash' sound comes from hitting the edge of the pad.

In reality, there are ribbon switches (like mobile phone keypads) underneath the bell & edge areas of the pad that detect hits to these areas.

solution!! you go to "voice" hit the hihat pedal, then press "page" till you get to hhat ofset and bring the value to negative. approx -25. pressure that you applied to hhat pedal becomes less