Precision fan keeps cycling between on and off

Posted this in the M6400 thread, but I'm getting frustrated with this so here it goes..

I replaced the FX3700M card with M7820 and now both fans are continuously cycling between on and off states each second or so and I don't know what to do about it. When I replaced it, I also put a new CPU fan (a Sunon Maglev with different current rating of 0.38A than the Forceconn with 0.5A that I used to replace the original one two years ago), but I've tried several fan combinations since and the fans are still giving me the works.

One potential cause might be related to a fact that for a short while mid way I couldn't unscrew one display holding screw so I put the battery back thinking that I won't be able to make it. Then I went an bought a new small flat screwdriver and did it and tinkered around a bit with the battery still in so maybe smth got damaged, but the funny thing is that I can boot the windows and install the GPU drivers so the only noticeable problem is this fan thing.

After dissasembling it for ten times I gave up so any possible solution would be very welcomed, thanks.

 

The problem seems to be caused by the inexisting fan readings - the engineer tool shows 0 RPM and it doesn't react to manual fan settings. I've tried changing the fans but the result is always the same - no fans are seen by the enginner tool or speedfan.

What could cause such an issue? Is there some CMOS I could reset? Is it possible that the fan readout inputs on the motherboard have been burned somehow?