IF the Circuit Board was faulty then the fridge would not cool on AC and/or on LP
Circuit board controls function of heat sources
Freezer (and food compartment) have 2 thermistors each
One to measure 'air' temp and one to measure 'surface' temp
Freezer temp sensing is factory pre-set (non-adjustable)...temp setting on Fridge control panel are for food compartment temp controls
*Freezer cooling process is first in line so it gets the coldest
On A/C temp setting is ~0*F and on Gas 7*F
The 'air' temp and 'surface' temp thermistors are used to control freezer fan and defrost cycles
Sounds like the freezer thermistors are failing NOT the Lower Circuit Board
Are you getting ANY error codes?
Is the Freezer fan working?
Does the fridge go into defrost mode ---should happen roughly every 24 hrs?
Have you placed a thermometer in freezer to compare temp vs displayed temp?
You can 'test' the thermistors resistance.
4 Pin P2 connector ---freezer (Pins 1 & 2/Air---- Pins 3 & 4/Surface)
4 pin P3 connector.....food (Pins 1 & 2/Air ------ Pins 3 & 4/Surface)
Pg 15 for info and Pg 49 for resistance values