Iron temp problem with 852D Station

[ROUGEXIII]

Hi,

I buy this YiHUA 852D station (a clone I guess) https://www.amazon.fr/Mbuynow-R%C3%A9paration-Temp%C3%A9rature-Contr%C3%B4l%C3%A9e-Professionnel/dp/B074C7RYLT
If the hot air gun seems to work, I didn't arrive to solder with the Iron.
After checking the real temperature, I understood why: the extremity of the Iron is a lot less hot than asked (see attachments)

For 500°C asked (the maximum) to get 351°C...


The heating element:


The heating element with 400°C asked:



I see many other buyer had the same issue in the comments,
any chance this is repairable?

Edit: Subsidiary question: you think it is possible to display the real temperature from the thermocouple on a small digit display (with an arduino if needed)?