LM567 issue

Hello,

im at my wits end. Im doing a project for University, i have to do an entire manufacture run in 10 weeks... so its not 3 weeks from deadline and the PCB is made but the tone decoder is doing something odd!!

https://s766.photobucket.com/albums/xx307/reacherjack/?action=view&current=image.png

I hope the image works, if not i will find one and post values.

the problem is that the signal is LOW when NOT recierving. this is a massive problem as when the sensor has no signal it it floats high...

Anyone got any ideas? anything i can try even if its an insane suggestion?

thanks!

image.png picture by reacherjack - Photobucket

that should be a link that works :S i hope!

ok now that im waking up a bit, sorry long week, the frequency that im trying to detect is 40k Hz (give or take). im fairly confident that the 18k resistor is too low. but i dont see that causing the problem im seeing.

any help will be really appreciated.

R1 in its datasheet is connected differently than yours.