no response from Serial1-Serial3

I have just replaced one 2560 clone with a different type as a result of the first board getting fried. The 2560 board is connected to a Serial-TTL converter http://www.dx.com/p/rs232-serial-port-to-ttl-converter-module-w-transmitting-and-receiving-indicator-144192

The old 2560 worked just fine but now the line
if (Serial2.available()==0) Serial.print ("Comms failure");

always returns the failure

My question is whether there is a way to test where the problem may be?

If you had a USB-TTL adapter, I would try that and see what that does with your new 2560.

no, don't have one. I see 4 possibilities

  1. There is a fault with the new board
  2. The rs232 adapter got fried at the same time as the old board. But the LED lights flash in a somewhat convincing way
  3. My serial device that I am connecting to, for some reason, is now malfunctioning.
  4. newbie error that I can't think of

ML999:
no, don't have one

well, there you go.
that's stop here.

Isn’t it possible to do some kind of cross-over between the serial ports to test them? or use a multimeter?

actually, I've found I do have a usb/RS232 converter - what would be a good way to test?

Not a USB-RS232 converter.

A USB-TTL adapter such as http://www.ebay.com/itm/2X-PL2303HX-USB-Adaptor-Replaces-FT232-USB-TTL-UART-3-3-5V-for-Arduino-USA-/201842465232

It will give you another way to communicate with your 2560's serial ports.
It may help you figure out whether it is the serial port on your new board or your dx.com board that is at fault.

ML999:
My question is whether there is a way to test where the problem may be?

First check that you actually have serial data coming into the Serial2 port.

An oscilloscope is real handy for testing this sort of stuff.

Actually I have no idea if hte adapter I have is USB/TTL or USB/RS232. Not sure how to tell the difference. Assuming it is RS232, could I put the USB/RS232 adapter on a laptop with a terminal, connect it to the TTL shield on the arduino, and have something running on the arduino that echoes keystrokes on the laptop?

ML999:
Isn't it possible to do some kind of cross-over between the serial ports to test them? or use a multimeter?

A Mega should have no problem sending data from Serial1 to Serial2 using a couple of jumper cables - but I have not tested that

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data.

...R