Hi, Alfi1966
Thanks very much!
I got everything sorted out in the oddest of fashions.
I found a repair shop, showed them you advice and photos and left my phone there to be repaired overnight.
They said that was the first Fairphone that ever fell into their hands (in fact, they had never heard about it) but they told me it was going to be ok.
Next morning, they called me on my replacement phone and warned me: “Beware, we’ve found out that on the flip side of the mainboard, just opposite the Wi-Fi chip, are the processor and the memory! If we apply heat to the pins of the Wi-Fi chip, there is a chance we will toast the processor or the memory and destroy your phone! We don’t know the chances there are for this to happen, since this is the first Fairphone we repair. We just wanted you to know that and we ask you to give us authorization to take the risk.”
I thought: “well, better a Fairphone with no Wi-Fi than no Fairphone at all” and told them to abort and that I would be picking up my phone this same afternoon.
I was sad, and a little bit hopeless. I thought that I would never get my Wi-Fi working again.
Half an hour later, I got another call from the repair shop: “Sorry, your phone is dead. When I told the technician not to repair it, he told me he already did, and, as he feared, it is no more (it has ceased to be, it has kicked the bucket, it has gone to meet it’s maker)… BUT. As it was us who screwed it by trying to repair it when you told us to abort, we are willing to give you another phone for free. ¡A better one!”
I explained that that was not ok for me, and I told them the reasons why I had this phone and why I didn’t want any other “non fair” phone. FP1(U) is not being produced any more and FP2 is too expensive for them to buy it.
So the guy told me to hold on while he looked on the Fairphone web, and came with the solution of buying a spare FP1U motherboard and installing it new on my FP1 for free.
So now I have a PF1 with a new FP1U motherboard (and a new daughterboard, If you have read the previous messages) for free 
and with working Wi-Fi.
On top of that, the guy told me that, even if they lost money, they learned about the Fairphone, discovered it sells a lot of spare parts and they are thinking in adding it to the list of phones they repair.
TL:DR
The guys in the repair shop fixed the Wi-Fi, for free, sort of… phew.