PCB or temp problem

Hi
Have used my Mono Mendel one year time without problems.
But now when I press the print button begins the table temperature to rise.
You can not turn it off with printer interface, I need to turn the power switch off.
Can´t se any burned parts on the PCB.
I have checked the temp sensors and they seem to work as they should.
Tested according to the instruction
[reprappro.com]

The first time the error noticed was when I printed a fairly high detail.
When I try to lower the table temperature, but it began to rise instead.

Thinking if I buy a new circuit board and cause of the error is still there,
and the new one crasch to.
But clearly if I replace hot end parts too so should not be the any foult remain.

The PCBcard is called Mono Mendel Revision: 2013-05-08
Is there something I can take another look at.



Christer
Sweden

Hi
Reprap Melzi V2.0 is stamped on PCB

Christer

Is the thermistor still firmly in contact with the bed?

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MakerFarm 8" Prusa i3v
RAMPS 1.4
0.4mm E3D v6 for 1.75mm

Hi
Yes it shows the value in the program.
And comparing with a thermometer, it shows the same temperature.
I have also been looking for any short circuit between the thermistor and element in bed.
Even in the hotend.
Thermistor - power connections for hotend heater- metal parts.
No short circuit.

Christer