MAX6675 0 data when using power from DC adapter

im using MAX6675 on my arduino mega for project, everytime i tried to power it with DC adapter the temperature is always 0 but when i powered it from it shows the temperature data normally
did anyone had this problem before?

Hi,
Please give us more details.

when i powered it from it

???

terryking228:
Hi,
Please give us more details.
???

im building a temperature controlled soldering iron with type E thermocouple and max6657 for the temperature sensor. the problem is when i use usb connection to power the arduino the sensor works normally it display the temperature on lcd just fine but when i unplug the usb and use 12v adapter/power supply to power the arduino i have no reading it only displayed 0
the power supply current is only 1A im also using PIR,buzzer & SSR do i need more current?