max232 not working, please help

[devil6600]

i have build a circuit containing max232 and some capacitor as per datasheet. but for some reason the circuit is not working. when i send some data from my pc to max232 i get an echo. but when i remove the max232 chip from the circuit and then send something i don't get echo, i don't know what's going wrong. i have tried replacing max232 but same problem. please help :sad:
please check the pcb layout, this is i am using.

 

[alexan_e]

You circuit is fine, i suppose your power supply is 5v and ok,
how are you testing the circuit, you are creating a loop that starts and ends to the pc? (send and receive)
You say you have no echo when you remove the chip, if you are doing what i said above then how can you have an echo if you remove the chip,
please explain what you mean.

Alex

 

[devil6600]

You circuit is fine, i suppose your power supply is 5v and ok,
how are you testing the circuit, you are creating a loop that starts and ends to the pc? (send and receive)
You say you have no echo when you remove the chip, if you are doing what i said above then how can you have an echo if you remove the chip,
please explain what you mean.

Alex

thanks for your reply.
for power supply i am using 7805 regulator IC
i am connecting 9 pin male port from PC to the circuit, and when i send any character at any baudrate i immediately receive its echo, whether max232 is powered on or off i am just receiving echo when ever i send any character. The other side of max232 (cmos-ttl) is also not connected, but still i receive echo.

 

[ckshivaram]

disable the echo in hyperterminal and see its response....

---------- Post added at 21:15 ---------- Previous post was at 21:14 ----------

see if the tx and rx pin in max 232 is shorted....

 

[alexan_e]

There nothing in your circuit to explain that echo so as ckshivaram said check your PCB soldering.
Was the cable ready made or did you make it, is it possible that there is a connection mistake there,
the cable should be "straight", pins 2 and 3 go to the same pins on the other side , not inverted.

Alex

 

[devil6600]

when i remove the max232 from the circuit i didn't get echo, it means its not short circuited, also i have checked continuity using multimeter, i didn't find it to be short.

i have tried swapping the pins, i used another female connector at the PC end and connected max232 circuit female connector using wires, tried swapping the pins but still the same result. :sad:

 

[alexan_e]

Is the serial plug gnd connected to your pcb gnd?

Alex

---------- Post added at 18:35 ---------- Previous post was at 18:31 ----------

The ground of the plug is pin 5

Alex

 

[ckshivaram]

i had this problem long back few times....

could you restart the pc and tr..

in your circuit db9 connector pin 5 is not connected to gnd of max or board.. check it

 

[devil6600]

thanks guys.
i suspect there is some defect in the 9pin cable, i use this cable to extend port. i checked the continuity once again and found that both the pins are short, so i am installing a usb-serial cable and then i'll check if i have the issue.
is it necessary to connect ground of 9pin connector? some time back i have made a circuit only for receiver part and did not connected ground pin and it was working. okl i'll connect ground and then i'll check it.

 

[alexan_e]

I haven't seen a floating ground MAX232 circuit, i don't know it it would work or not ,
the grounds gives a common reference point in both sides (pc ans chip).

Alex