Heatbed get not at temperature

I have a mk2b heatbed with 24 volt power supply and on top a 5 mm aluminium pei print surface but its only get 80 degrees what can there be the problem it not getting 100 degrees.

This is a guess.
What is the current rating of the power supply?

It got 320 watt 13,40 amp

Did you check the voltage on the power supply?

No but what can there be wrong with it is a 24 v powersupplei

This is a starting place.
Maybe the power supply is defective and only putting 15 volts.
Maybe the bed is defective.
Maybe the circuit that drives the bed from the control board is having an issue.

You have to start somewhere.
I always start with checking the voltage.

Oké i try that first than

I have check the voltage but it 27,1 volt one al the components one the power supply there you can turn a Screw its say on ADJ and a arrrow that points From A to V+ can i turn there the voltage down

The Screw is for adjust the voltage of the power supply i have adjust to 24 volt but with no result is it possible that the heatbed not so good one

Assuming your electronics can handle it, I would turn the voltage up to above 24V - (be careful not to overload the power supply, as you increase the voltage the amperage/current will also increase so be sure to stay within the limits of both the supply and the electronics).

My MK3 heatbed (also wired for 24V) can’t reach more than ~90C with a 24V supply, in order to get higher temperatures I need to increase the voltage - I usually run it around 30 V from my adjustable power supply. Measuring the voltage and current it is clear to see that the resistance of the heated bed increases as it heats up hence to keep the wattage/power high enough to reach high temperatures the voltage/current needs to get higher as the temperature increases.

Stick RPG 2 unblocked It’s hard to say.