Arduino Mega2560 with Ethernetshield crashes every 32 seconds only on DC power

hello,

i've made terrarium controller using arduino mega 2560 , ethernet shield. arduino crashes every or 32 seconds. when powered dc power supply (9v 1.67 a). if connect  my mac using usb, doesn't crash. doesn't happen if connect ethernet port of shield mac (crossover cable).

memory consumption of sketch ok, there 4k of free memory time (monitored using rrd).

the sketch source: https://github.com/tlinden/terraduino/blob/master/terraduino/terraduino.ino (libraries used: https://github.com/tlinden/terraduino/tree/master/libraries).

the interesting thing is, older version of sketch didn't have problem: https://github.com/tlinden/terraduino/blob/3d102cbde9d5804049617f4ea5a2d04088d9ee8b/terraduino/terraduino.ino. since added default gateway along code change webinterface , eeprom code (in libraries/eeany/). if go version, no crash occurs.

since doesn't happen when connect usb, can't troubleshoot it.

is there can me that?

edit: tried old version mentioned above , crashes occur (although  it run version uninterrupted 3 days).

[update[/b]: removed stuff loop() (and deactivated wdt), runs empty loop() , nothing. however, still crashes regularly.

start monitoring external supply , 5v node.  could faulty supply.

also, verify dc supply , not 9v ac.

in terms of microprocessor, processor running empty loop or executing instructions uses same amount of power.

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